## Guide to the Secure Configuration of Red Hat Enterprise Linux 7

> with profile STIG for Red Hat Enterprise Linux 7 Workstation
> This is a *draft* profile for STIG. This profile is being developed under the DoD consensus model to become a STIG in coordination with DISA FSO.

> Where is the RHEL7 STIG?

> - Question: May I deploy a product if no STIG exists?
>   Answer: Yes, based on mission need and with DAA approval.
> - Question: What do I use if there is no STIG?
>   Answer: DISA FSO developed Security Requirement Guides (SRGs) to address technology areas. In the absence of a STIG, an SRG can be used to determine compliance with DoD policies. If there is no applicable SRG or STIG, industry or vendor recommended practices may be used. Examples include Center for Internet Security Benchmarks, Payment Card Industry requirements or the vendor's own security documentation.
> Source: http://iase.disa.mil/stigs/Pages/faqs.aspx#STIG

The SCAP Security Guide Project
https://www.open-scap.org/security-policies/scap-security-guide
This guide presents a catalog of security-relevant configuration settings for Red Hat Enterprise Linux 7. It is a rendering of content structured in the eXtensible Configuration Checklist Description Format (XCCDF) in order to support security automation. The SCAP content is is available in the `scap-security-guide` package which is developed at https://www.open-scap.org/security-policies/scap-security-guide.
Providing system administrators with such guidance informs them how to securely configure systems under their control in a variety of network roles. Policy makers and baseline creators can use this catalog of settings, with its associated references to higher-level security control catalogs, in order to assist them in security baseline creation. This guide is a catalog, not a checklist, and satisfaction of every item is not likely to be possible or sensible in many operational scenarios. However, the XCCDF format enables granular selection and adjustment of settings, and their association with OVAL and OCIL content provides an automated checking capability. Transformations of this document, and its associated automated checking content, are capable of providing baselines that meet a diverse set of policy objectives. Some example XCCDF Profiles, which are selections of items that form checklists and can be used as baselines, are available with this guide. They can be processed, in an automated fashion, with tools that support the Security Content Automation Protocol (SCAP). The DISA STIG for Red Hat Enterprise Linux 7, which provides required settings for US Department of Defense systems, is one example of a baseline created from this guidance.
Do not attempt to implement any of the settings in this guide without first testing them in a non-operational environment. The creators of this guidance assume no responsibility whatsoever for its use by other parties, and makes no guarantees, expressed or implied, about its quality, reliability, or any other characteristic.

Profile Title | STIG for Red Hat Enterprise Linux 7 Workstation
Profile ID | xccdf_org.ssgproject.content_profile_stig-rhel7-workstation-upstream

## Revision History

Current version: 0.1.31

- draft (as of 2017-08-11)

## Platforms

- cpe:/o:redhat:enterprise_linux:7
- cpe:/o:redhat:enterprise_linux:7::client
- cpe:/o:redhat:enterprise_linux:7::computenode

## Table of Contents

1. System Settings

1. Installing and Maintaining Software
2. File Permissions and Masks
3. SELinux
4. Account and Access Control
5. Network Configuration and Firewalls
6. Configure Syslog
7. System Accounting with auditd

2. Services

1. Obsolete Services
2. Base Services
3. Cron and At Daemons
4. SSH Server
5. System Security Services Daemon
6. Network Time Protocol
7. LDAP
8. NFS and RPC
9. FTP Server
10. Network Routing
11. SNMP Server

## Checklist

contains 251 rules

### System Settings [ref]group

Contains rules that check correct system settings.

contains 188 rules

### Installing and Maintaining Software [ref]group

The following sections contain information on security-relevant choices during the initial operating system installation process and the setup of software updates.

contains 57 rules

### Disk Partitioning [ref]group

To ensure separation and protection of data, there are top-level system directories which should be placed on their own physical partition or logical volume. The installer's default partitioning scheme creates separate logical volumes for `/`, `/boot`, and `swap`.

- If starting with any of the default layouts, check the box to "Review and modify partitioning." This allows for the easy creation of additional logical volumes inside the volume group already created, though it may require making `/`'s logical volume smaller to create space. In general, using logical volumes is preferable to using partitions because they can be more easily adjusted later.
- If creating a custom layout, create the partitions mentioned in the previous paragraph (which the installer will require anyway), as well as separate ones described in the following sections.

If a system has already been installed, and the default partitioning scheme was used, it is possible but nontrivial to modify it to create separate logical volumes for the directories listed above. The Logical Volume Manager (LVM) makes this possible. See the LVM HOWTO at http://tldp.org/HOWTO/LVM-HOWTO/ for more detailed information on LVM.

contains 5 rules

#### Ensure /tmp Located On Separate Partition [ref]rule

The `/tmp` directory is a world-writable directory used for temporary file storage. Ensure it has its own partition or logical volume at installation time, or migrate it using LVM.

Rationale:

The `/tmp` partition is used as temporary storage by many programs. Placing `/tmp` in its own partition enables the setting of more restrictive mount options, which can help protect programs which use it.

Severity: low

Identifiers: CCE-27173-4

References: SC-32(1), 366, SRG-OS-000480-GPOS-00227, 1.1.1, RHEL-07-021270

#### Ensure /var Located On Separate Partition [ref]rule

The `/var` directory is used by daemons and other system services to store frequently-changing data. Ensure that `/var` has its own partition or logical volume at installation time, or migrate it using LVM.

Rationale:

Ensuring that `/var` is mounted on its own partition enables the setting of more restrictive mount options. This helps protect system services such as daemons or other programs which use it. It is not uncommon for the `/var` directory to contain world-writable directories installed by other software packages.

Severity: low

Identifiers: CCE-26404-4

References: SC-32(1), 1.1.5, 366, SRG-OS-000480-GPOS-00227, RHEL-07-021250

#### Ensure /var/log/audit Located On Separate Partition [ref]rule

Audit logs are stored in the `/var/log/audit` directory. Ensure that it has its own partition or logical volume at installation time, or migrate it later using LVM. Make absolutely certain that it is large enough to store all audit logs that will be created by the auditing daemon.

Rationale:

Placing `/var/log/audit` in its own partition enables better separation between audit files and other files, and helps ensure that auditing cannot be halted due to the partition running out of space.

Severity: low

Identifiers: CCE-26971-2

References: AU-4, AU-9, SC-32(1), 366, 1.1.8, SRG-OS-000480-GPOS-00227, RHEL-07-021260

#### Ensure /home Located On Separate Partition [ref]rule

If user home directories will be stored locally, create a separate partition for `/home` at installation time (or migrate it later using LVM). If `/home` will be mounted from another system such as an NFS server, then creating a separate partition is not necessary at installation time, and the mountpoint can instead be configured later.

Rationale:

Ensuring that `/home` is mounted on its own partition enables the setting of more restrictive mount options, and also helps ensure that users cannot trivially fill partitions used for log or audit data storage.

Severity: low

Identifiers: CCE-80144-9

References: SC-32(1), 366, 1208, 1.1.9, SRG-OS-000480-GPOS-00227, RHEL-07-021240

#### Encrypt Partitions [ref]rule

Red Hat Enterprise Linux 7 natively supports partition encryption through the Linux Unified Key Setup-on-disk-format (LUKS) technology. The easiest way to encrypt a partition is during installation time.
For manual installations, select the `Encrypt` checkbox during partition creation to encrypt the partition. When this option is selected the system will prompt for a passphrase to use in decrypting the partition. The passphrase will subsequently need to be entered manually every time the system boots.
For automated/unattended installations, it is possible to use Kickstart by adding the `--encrypted` and `--passphrase=` options to the definition of each partition to be encrypted. For example, the following line would encrypt the root partition:

    part / --fstype=ext4 --size=100 --onpart=hda1 --encrypted --passphrase=PASSPHRASE

Any PASSPHRASE is stored in the Kickstart in plaintext, and the Kickstart must then be protected accordingly. Omitting the `--passphrase=` option from the partition definition will cause the installer to pause and interactively ask for the passphrase during installation.
Detailed information on encrypting partitions using LUKS can be found on the Red Hat Documentation web site:
https://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/7/html/Security_Guide/sec-Encryption.html Rationale:

The risk of a system's physical compromise, particularly mobile systems such as laptops, places its data at risk of compromise. Encrypting this data mitigates the risk of its loss if the system is lost.

Severity: high

Identifiers: CCE-27128-8

References: SC-13, SC-28(1), 1199, 2476, SRG-OS-000405-GPOS-00184, SRG-OS-000185-GPOS-00079, RHEL-07-020170

### Updating Software [ref]group

The `yum` command line tool is used to install and update software packages. The system also provides a graphical software update tool in the System menu, in the Administration submenu, called Software Update.
Red Hat Enterprise Linux systems contain an installed software catalog called the RPM database, which records metadata of installed packages. Consistently using `yum` or the graphical Software Update for all software installation allows for insight into the current inventory of installed software on the system.

contains 7 rules

#### Ensure Red Hat GPG Key Installed [ref]rule

To ensure the system can cryptographically verify base software packages come from Red Hat (and to connect to the Red Hat Network to receive them), the Red Hat GPG key must properly be installed. To install the Red Hat GPG key, run:

    $ sudo rhn_register

If the system is not connected to the Internet or an RHN Satellite, then install the Red Hat GPG key from trusted media such as the Red Hat installation CD-ROM or DVD. Assuming the disc is mounted in `/media/cdrom`, use the following command as the root user to import it into the keyring:

    $ sudo rpm --import /media/cdrom/RPM-GPG-KEY

Rationale:

Changes to software components can have significant effects on the overall security of the operating system. This requirement ensures the software has not been tampered with and that it has been provided by a trusted vendor. The Red Hat GPG key is necessary to cryptographically verify packages are from Red Hat.

Severity: high

Identifiers: CCE-26957-1

References: CM-5(3), SI-7, MA-1(b), 1749, 366, Req-6.2, 1.2.2

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # The two fingerprints below are retrieved from https://access.redhat.com/security/team/key
    readonly REDHAT_RELEASE_2_FINGERPRINT="567E 347A D004 4ADE 55BA 8A5F 199E 2F91 FD43 1D51"
    readonly REDHAT_AUXILIARY_FINGERPRINT="43A6 E49C 4A38 F4BE 9ABF 2A53 4568 9C88 2FA6 58E0"
    # Location of the key we would like to import (once it's integrity verified)
    readonly REDHAT_RELEASE_KEY="/etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release"

    RPM_GPG_DIR_PERMS=$(stat -c %a "$(dirname "$REDHAT_RELEASE_KEY")")

    # Verify /etc/pki/rpm-gpg directory permissions are safe
    if [ "${RPM_GPG_DIR_PERMS}" -le "755" ]
    then
      # If they are safe, try to obtain fingerprints from the key file
      # (to ensure there won't be e.g. CRC error)
      IFS=$'\n' GPG_OUT=($(gpg --with-fingerprint "${REDHAT_RELEASE_KEY}"))
      GPG_RESULT=$?
      # No CRC error, safe to proceed
      if [ "${GPG_RESULT}" -eq "0" ]
      then
        for ITEM in "${GPG_OUT[@]}"
        do
          # Filter just hexadecimal fingerprints from gpg's output from
          # processing of a key file
          RESULT=$(echo ${ITEM} | sed -n "s/[[:space:]]*Key fingerprint = \(.*\)/\1/p" | tr -s '[:space:]')
          # If fingerprint matches Red Hat's release 2 or auxiliary key import the key
          if [[ ${RESULT} ]] && ([[ ${RESULT} = "${REDHAT_RELEASE_2_FINGERPRINT}" ]] || \
                                 [[ ${RESULT} = "${REDHAT_AUXILIARY_FINGERPRINT}" ]])
          then
            rpm --import "${REDHAT_RELEASE_KEY}"
          fi
        done
      fi
    fi

#### Ensure gpgcheck Enabled In Main Yum Configuration [ref]rule

The `gpgcheck` option controls whether RPM packages' signatures are always checked prior to installation. To configure yum to check package signatures before installing them, ensure the following line appears in `/etc/yum.conf` in the `[main]` section:

    gpgcheck=1

Rationale:

Changes to any software components can have significant effects on the overall security of the operating system. This requirement ensures the software has not been tampered with and that it has been provided by a trusted vendor.
Accordingly, patches, service packs, device drivers, or operating system components must be signed with a certificate recognized and approved by the organization.
Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA).

Severity: high

Identifiers: CCE-26989-4

References: CM-5(3), SI-7, MA-1(b), 1749, SRG-OS-000366-GPOS-00153, RHEL-07-020150, Req-6.2, 1.2.3

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    sed -i 's/gpgcheck=.*/gpgcheck=1/g' /etc/yum.conf

#### Ensure gpgcheck Enabled For All Yum Package Repositories [ref]rule

To ensure signature checking is not disabled for any repos, remove any lines from files in `/etc/yum.repos.d` of the form:

    gpgcheck=0

Rationale:

Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. Certificates used to verify the software must be from an approved Certificate Authority (CA).

Severity: high

Identifiers: CCE-26876-3

References: CM-5(3), SI-7, MA-1(b), 1749, 366, Req-6.2

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    sed -i 's/gpgcheck=.*/gpgcheck=1/g' /etc/yum.repos.d/*

#### Ensure Software Patches Installed [ref]rule

If the system is joined to the Red Hat Network, a Red Hat Satellite Server, or a yum server, run the following command to install updates:

    $ sudo yum update

If the system is not configured to use one of these sources, updates (in the form of RPM packages) can be manually downloaded from the Red Hat Network and installed using `rpm`.
NOTE: U.S. Defense systems are required to be patched within 30 days or sooner as local policy dictates. Rationale:

Installing software updates is a fundamental mitigation against the exploitation of publicly-known vulnerabilities. If the most recent security patches and updates are not installed, unauthorized users may take advantage of weaknesses in the unpatched software. The lack of prompt attention to patching could result in a system compromise.

Severity: high

Identifiers: CCE-26895-3

References: SI-2, SI-2(c), MA-1(b), 366, Req-6.2, 1.7, SRG-OS-000480-GPOS-00227, RHEL-07-020250

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    yum -y update

#### Ensure YUM Removes Previous Package Versions [ref]rule

`Yum` should be configured to remove previous software components after previous versions have been installed. To configure `yum` to remove the previous software components after updating, set the `clean_requirements_on_remove` to `1` in `/etc/yum.conf`.

Rationale:

Previous versions of software components that are not removed from the information system after updates have been installed may be exploited by some adversaries.

Severity: low

Identifiers: CCE-80346-0

References: SI-2(6), 2617, SRG-OS-000437-GPOS-00194, RHEL-07-020200

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    if grep --silent ^clean_requirements_on_remove /etc/yum.conf ; then
            sed -i "s/^clean_requirements_on_remove.*/clean_requirements_on_remove=1/g" /etc/yum.conf
    else
            echo -e "\n# Set clean_requirements_on_remove to 1 per security requirements" >> /etc/yum.conf
            echo "clean_requirements_on_remove=1" >> /etc/yum.conf
    fi

#### Ensure gpgcheck Enabled for Local Packages [ref]rule

`Yum` should be configured to verify the signature(s) of local packages prior to installation. To configure `yum` to verify signatures of local packages, set the `localpkg_gpgcheck` to `1` in `/etc/yum.conf`.

Rationale:

Changes to any software components can have significant effects to the overall security of the operating system. This requirement ensures the software has not been tampered and has been provided by a trusted vendor.
Accordingly, patches, service packs, device drivers, or operating system components must be signed with a certificate recognized and approved by the organization.

Severity: high

Identifiers: CCE-80347-8

References: CM-5(3), 1749, SRG-OS-000366-GPOS-00153, RHEL-07-020151

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    if grep --silent ^localpkg_gpgcheck /etc/yum.conf ; then
            sed -i "s/^localpkg_gpgcheck.*/localpkg_gpgcheck=1/g" /etc/yum.conf
    else
            echo -e "\n# Set localpkg_gpgcheck to 1 per security requirements" >> /etc/yum.conf
            echo "localpkg_gpgcheck=1" >> /etc/yum.conf
    fi

#### Ensure gpgcheck Enabled for Repository Metadata [ref]rule

Verify the operating system prevents the installation of patches, service packs, device drivers, or operating system components of local packages without verification of the repository metadata.
Check that `yum` verifies the repository metadata prior to install with the following command. This should be configured by setting `repo_gpgcheck` to `1` in `/etc/yum.conf`.

Rationale:

Changes to any software components can have significant effects to the overall security of the operating system. This requirement ensures the software has not been tampered and has been provided by a trusted vendor.
Accordingly, patches, service packs, device drivers, or operating system components must be signed with a certificate recognized and approved by the organization.
Verifying the authenticity of the software prior to installation validates the integrity of the patch or upgrade received from a vendor. This ensures the software has not been tampered with and that it has been provided by a trusted vendor. Self-signed certificates are disallowed by this requirement. The operating system should not have to verify the software again.
NOTE: For U.S. Military systems, this requirement does not mandate DoD certificates for this purpose; however, the certificate used to verify the software must be from an approved Certificate Authority.

Severity: high

Identifiers: CCE-80348-6

References: CM-5(3), 1749, SRG-OS-000366-GPOS-00153, RHEL-07-020152

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    if grep --silent ^repo_gpgcheck /etc/yum.conf ; then
            sed -i "s/^repo_gpgcheck.*/repo_gpgcheck=1/g" /etc/yum.conf
    else
            echo -e "\n# Set repo_gpgcheck to 1 per security requirements" >> /etc/yum.conf
            echo "repo_gpgcheck=1" >> /etc/yum.conf
    fi

### System and Software Integrity [ref]group

System and software integrity can be gained by installing antivirus, increasing system encryption strength with FIPS, verifying installed software, enabling SELinux, installing an Intrusion Prevention System, etc. However, installing or enabling integrity checking tools cannot prevent intrusions, but they can detect that an intrusion may have occurred. Requirements for integrity checking may be highly dependent on the environment in which the system will be used. Snapshot-based approaches such as AIDE may induce considerable overhead in the presence of frequent software updates.

contains 19 rules

### Software Integrity Checking [ref]group

Both the AIDE (Advanced Intrusion Detection Environment) software and the RPM package management system provide mechanisms for verifying the integrity of installed software. AIDE uses snapshots of file metadata (such as hashes) and compares these to current system files in order to detect changes.
The RPM package management system can conduct integrity checks by comparing information in its metadata database with files installed on the system.

contains 9 rules

### Verify Integrity with AIDE [ref]group

AIDE conducts integrity checks by comparing information about files with previously-gathered information. Ideally, the AIDE database is created immediately after initial system configuration, and then again after any software update. AIDE is highly configurable, with further configuration information located in `/usr/share/doc/aide-VERSION`.

contains 7 rules

#### Install AIDE [ref]rule

Install the AIDE package with the command:

    $ sudo yum install aide

Rationale:

The AIDE package must be installed if it is to be available for integrity checking.

Severity: medium

Identifiers: CCE-27096-7

References: CM-3(d), CM-3(e), CM-6(d), CM-6(3), SC-28, SI-7, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-11.5, 1.3.1

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command install aide

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    - name: Ensure aide is installed
      package:
        name="{{item}}"
        state=present
      with_items:
        - aide

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    include install_aide

    class install_aide {
      package { 'aide':
        ensure => 'installed',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    package --add=aide

#### Build and Test AIDE Database [ref]rule

Run the following command to generate a new database:

    $ sudo /usr/sbin/aide --init

By default, the database will be written to the file `/var/lib/aide/aide.db.new.gz`. Storing the database, the configuration file `/etc/aide.conf`, and the binary `/usr/sbin/aide` (or hashes of these files), in a secure location (such as on read-only media) provides additional assurance about their integrity. The newly-generated database can be installed as follows:

    $ sudo cp /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz

To initiate a manual check, run the following command:

    $ sudo /usr/sbin/aide --check

If this check produces any unexpected output, investigate. Rationale:

For AIDE to be effective, an initial database of "known-good" information about files must be captured and it should be able to be verified against the installed files.

Severity: medium

Identifiers: CCE-27220-3

References: CM-3(d), CM-3(e), CM-6(d), CM-6(3), SC-28, SI-7, Req-11.5

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    /usr/sbin/aide --init
    /bin/cp -p /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz

#### Configure Periodic Execution of AIDE [ref]rule

At a minimum, AIDE should be configured to run a weekly scan. At most, AIDE should be run daily. To implement a daily execution of AIDE at 4:05am using cron, add the following line to `/etc/crontab`:

    05 4 * * * root /usr/sbin/aide --check

To implement a weekly execution of AIDE at 4:05am using cron, add the following line to `/etc/crontab`:

    05 4 * * 0 root /usr/sbin/aide --check

AIDE can be executed periodically through other means; this is merely one example. Rationale:

By default, AIDE does not install itself for periodic execution. Periodically running AIDE is necessary to reveal unexpected changes in installed files.
Unauthorized changes to the baseline configuration could make the system vulnerable to various attacks or allow unauthorized access to the operating system. Changes to operating system configurations can have unintended side effects, some of which may be relevant to security.
Detecting such changes and providing an automated response can help avoid unintended, negative consequences that could ultimately affect the security state of the operating system. The operating system's Information Management Officer (IMO)/Information System Security Officer (ISSO) and System Administrators (SAs) must be notified via email and/or monitoring system trap when there is an unauthorized modification of a configuration item.

Severity: medium

Identifiers: CCE-26952-2

References: CM-3(d), CM-3(e), CM-3(5), CM-6(d), CM-6(3), SC-28, SI-7, 1744, Req-11.5, 1.3.1, SRG-OS-000363-GPOS-00150, 020130

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    echo "05 4 * * * root /usr/sbin/aide --check" >> /etc/crontab

#### Configure Notification of Post-AIDE Scan Details [ref]rule

AIDE should notify appropriate personnel of the details of a scan after the scan has been run. If AIDE has already been configured for periodic execution in `/etc/crontab`, append the following line to the existing AIDE line:

     | /bin/mail -s "$(hostname) - AIDE Integrity Check" root@localhost

Otherwise, add the following line to `/etc/crontab`:

    05 4 * * * root /usr/sbin/aide --check | /bin/mail -s "$(hostname) - AIDE Integrity Check" root@localhost

AIDE can be executed periodically through other means; this is merely one example. Rationale:

Unauthorized changes to the baseline configuration could make the system vulnerable to various attacks or allow unauthorized access to the operating system. Changes to operating system configurations can have unintended side effects, some of which may be relevant to security.
Detecting such changes and providing an automated response can help avoid unintended, negative consequences that could ultimately affect the security state of the operating system. The operating system's Information Management Officer (IMO)/Information System Security Officer (ISSO) and System Administrators (SAs) must be notified via email and/or monitoring system trap when there is an unauthorized modification of a configuration item.

Severity: medium

Identifiers: CCE-80374-2

References: CM-3(5), 1744, SRG-OS-000363-GPOS-00150, 020140

#### Configure AIDE to Verify Access Control Lists (ACLs) [ref]rule

By default, the `acl` option is added to the `FIPSR` ruleset in AIDE. If using a custom ruleset or the `acl` option is missing, add `acl` to the appropriate ruleset. For example, add `acl` to the following line in `/etc/aide.conf`:

    FIPSR = p+i+n+u+g+s+m+c+acl+selinux+xattrs+sha256

AIDE rules can be configured in multiple ways; this is merely one example that is already configured by default. Rationale:

ACLs can provide permissions beyond those permitted through the file mode and must be verified by the file integrity tools.

Severity: medium

Identifiers: CCE-80375-9

References: SI-7.1, 366, SRG-OS-000480-GPOS-00227, 021600

#### Configure AIDE to Verify Extended Attributes [ref]rule

By default, the `xattrs` option is added to the `FIPSR` ruleset in AIDE. If using a custom ruleset or the `xattrs` option is missing, add `xattrs` to the appropriate ruleset. For example, add `xattrs` to the following line in `/etc/aide.conf`:

    FIPSR = p+i+n+u+g+s+m+c+acl+selinux+xattrs+sha256

AIDE rules can be configured in multiple ways; this is merely one example that is already configured by default. Rationale:

Extended attributes in file systems are used to contain arbitrary data and file metadata with security implications.

Severity: medium

Identifiers: CCE-80376-7

References: SI-7.1, 366, SRG-OS-000480-GPOS-00227, 021610

#### Configure AIDE to Use FIPS 140-2 for Validating Hashes [ref]rule

By default, the `sha512` option is added to the `NORMAL` ruleset in AIDE. If using a custom ruleset or the `sha512` option is missing, add `sha512` to the appropriate ruleset. For example, add `sha512` to the following line in `/etc/aide.conf`:

    NORMAL = FIPSR+sha512

AIDE rules can be configured in multiple ways; this is merely one example that is already configured by default. Rationale:

File integrity tools use cryptographic hashes for verifying file contents and directories have not been altered. These hashes must be FIPS 140-2 approved cryptographic hashes.

Severity: medium

Identifiers: CCE-80377-5

References: SI-7.1, 366, SRG-OS-000480-GPOS-00227, 021620

### Verify Integrity with RPM [ref]group

The RPM package management system includes the ability to verify the integrity of installed packages by comparing the installed files with information about the files taken from the package metadata stored in the RPM database. Although an attacker could corrupt the RPM database (analogous to attacking the AIDE database as described above), this check can still reveal modification of important files. To list which files on the system differ from what is expected by the RPM database:

    $ rpm -qVa

See the man page for `rpm` to see a complete explanation of each column.

contains 2 rules

#### Verify and Correct File Permissions with RPM [ref]rule

Discretionary access control is weakened if a user or group has access permissions to system files and directories greater than the default. The RPM package management system can check file access permissions of installed software packages, including many that are important to system security. Verify that the file permissions, ownership, and gruop membership of system files and commands match vendor values. Check the file permissions, ownership, and group membership with the following command:

    $ sudo rpm -Va | grep '^.M'

Output indicates files that do not match vendor defaults. After locating a file with incorrect permissions, run the following command to determine which package owns it:

    $ rpm -qf FILENAME

Next, run the following command to reset its permissions to the correct values:

    $ sudo rpm --setperms PACKAGENAME

Warning: Note: Due to a bug in the `gdm` package, the RPM verify command may continue to fail even after file permissions have been correctly set on `/var/log/gdm`. This is being tracked in Red Hat Bugzilla #1275532.
Rationale:

Permissions on system binaries and configuration files that are too generous could allow an unauthorized user to gain privileges that they should not have. The permissions set by the vendor should be maintained. Any deviations from this baseline should be investigated.

Severity: high

Identifiers: CCE-27209-6

References: AC-6, AU-9(1), AU-9(3), CM-6(d), CM-6(3), 1494, 1496, Req-11.5, 1.2.6, 6.1.3, 6.1.4, 6.1.5, 6.1.6, 6.1.7, 6.1.8, 6.1.9, 6.2.3, RHEL-07-010010, SRG-OS-000257-GPOS-00098, SRG-OS-000278-GPOS-00108

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Declare array to hold list of RPM packages we need to correct permissions for
    declare -a SETPERMS_RPM_LIST

    # Create a list of files on the system having permissions different from what
    # is expected by the RPM database
    FILES_WITH_INCORRECT_PERMS=($(rpm -Va --nofiledigest | grep '^.M'))

    # For each file path from that list:
    # * Determine the RPM package the file path is shipped by,
    # * Include it into SETPERMS_RPM_LIST array

    for FILE_PATH in "${FILES_WITH_INCORRECT_PERMS[@]}"
    do
    	RPM_PACKAGE=$(rpm -qf "$FILE_PATH")
    	SETPERMS_RPM_LIST=("${SETPERMS_RPM_LIST[@]}" "$RPM_PACKAGE")
    done

    # Remove duplicate mention of same RPM in $SETPERMS_RPM_LIST (if any)
    SETPERMS_RPM_LIST=( $(echo "${SETPERMS_RPM_LIST[@]}" | sort -n | uniq) )

    # For each of the RPM packages left in the list -- reset its permissions to the
    # correct values
    for RPM_PACKAGE in "${SETPERMS_RPM_LIST[@]}"
    do
    	rpm --setperms "${RPM_PACKAGE}"
    done

#### Verify File Hashes with RPM [ref]rule

Without cryptographic integrity protections, system executables and files can be altered by unauthorized users without detection. The RPM package management system can check the hashes of installed software packages, including many that are important to system security. To verify that the cryptographic hash of system files and commands match vendor values, run the following command to list which files on the system have hashes that differ from what is expected by the RPM database:

    $ rpm -Va | grep '^..5'

A "c" in the second column indicates that a file is a configuration file, which may appropriately be expected to change. If the file was not expected to change, investigate the cause of the change using audit logs or other means. The package can then be reinstalled to restore the file. Run the following command to determine which package owns the file:

    $ rpm -qf FILENAME

The package can be reinstalled from a yum repository using the command:

    $ sudo yum reinstall PACKAGENAME

Alternatively, the package can be reinstalled from trusted media using the command:

    $ sudo rpm -Uvh PACKAGENAME

Rationale:

The hashes of important files like system executables should match the information given by the RPM database. Executables with erroneous hashes could be a sign of nefarious activity on the system.

Severity: high

Identifiers: CCE-27157-7

References: CM-6(d), CM-6(3), SI-7(1), 663, Req-11.5, 1.2.6, RHEL-07-010020, SRG-OS-000480-GPOS-00227

### Endpoint Protection Software [ref]group

Endpoint protection security software that is not provided or supported by Red Hat can be installed to provide complementary or duplicative security capabilities to those provided by the base platform. Add-on software may not be appropriate for some specialized systems.

contains 6 rules

### McAfee Endpoint Security Software [ref]group

In DoD environments, McAfee Host-based Security System (HBSS) and VirusScan Enterprise for Linux (VSEL) is required to be installed on all systems.

contains 5 rules

### McAfee Host-Based Intrusion Detection Software (HBSS) [ref]group

McAfee Host-based Security System (HBSS) is a suite of software applications used to monitor, detect, and defend computer networks and systems.

contains 2 rules

#### Install the Asset Configuration Compliance Module (ACCM) [ref]rule

Install the Asset Configuration Compliance Module (ACCM).

Rationale:

Without a host-based intrusion detection tool, there is no system-level defense when an intruder gains access to a system or network. Additionally, a host-based intrusion prevention tool can provide methods to immediately lock out detected intrusion attempts.

Severity: medium

Identifiers: CCE-80126-6

References: SC-7, SI-4(1).1, 366, 1263, Req-11.4, STG-OS-000480-GPOS-00227, RHEL-07-030790

#### Install the Policy Auditor (PA) Module [ref]rule

Install the Policy Auditor (PA) Module.

Rationale:

Without a host-based intrusion detection tool, there is no system-level defense when an intruder gains access to a system or network. Additionally, a host-based intrusion prevention tool can provide methods to immediately lock out detected intrusion attempts.

Severity: medium

Identifiers: CCE-80369-2

References: SC-7, SI-4(1).1, 366, 1263, Req-11.4, STG-OS-000480-GPOS-00227, RHEL-07-TBD

#### Install McAfee Virus Scanning Software [ref]rule

Install McAfee VirusScan Enterprise for Linux antivirus software which is provided for DoD systems and uses signatures to search for the presence of viruses on the filesystem.

Rationale:

Virus scanning software can be used to detect if a system has been compromised by computer viruses, as well as to limit their spread to other systems.

Severity: high

Identifiers: CCE-80127-4

References: SC-28, SI-3, SI-3(1)(ii), 366, 1239, 1668, SRG-OS-000480-GPOS-00227, RHEL-07-030810

#### Enable nails Service [ref]rule

The `nails` service is used to run McAfee VirusScan Enterprise for Linux and McAfee Host-based Security System (HBSS) services. The `nails` service can be enabled with the following command:

    $ sudo systemctl enable nails.service

Rationale:

Virus scanning software can be used to detect if a system has been compromised by computer viruses, as well as to limit their spread to other systems.

Severity: medium

Identifiers: CCE-80128-2

References: SC-28, SI-3, SI-3(1)(ii), 366, 1239, 1668, SRG-OS-000480-GPOS-00227, RHEL-07-TBD

#### Virus Scanning Software Definitions Are Updated [ref]rule

Ensure virus definition files are no older than 7 days or their last release.

Rationale:

Virus scanning software can be used to detect if a system has been compromised by computer viruses, as well as to limit their spread to other systems.

Severity: medium

Identifiers: CCE-80129-0

References: SC-28, SI-3, SI-3(1)(ii), 366, 1239, 1668, SRG-OS-000480-GPOS-00227, RHEL-07-030820

#### Install Intrusion Detection Software [ref]rule

The base Red Hat platform already includes a sophisticated auditing system that can detect intruder activity, as well as SELinux, which provides host-based intrusion prevention capabilities by confining privileged programs and user sessions which may become compromised.

Warning: Note in DoD environments, supplemental intrusion detection tools, such as the McAfee Host-based Security System, are available to integrate with existing infrastructure. When these supplemental tools interfere with proper functioning of SELinux, SELinux takes precedence.
Rationale:

Host-based intrusion detection tools provide a system-level defense when an intruder gains access to a system or network.

Severity: high

Identifiers: CCE-26818-5

References: SC-7, 1263, Req-11.4

### Federal Information Processing Standard (FIPS) [ref]group

The Federal Information Processing Standard (FIPS) is a computer security standard which is developed by the U.S. Government and industry working groups to validate the quality of cryptographic modules. The FIPS standard provides four security levels to ensure adequate coverage of different industries, implementation of cryptographic modules, and organizational sizes and requirements.
FIPS 140-2 is the current standard for validating that mechanisms used to access cryptographic modules utilize authentication that meets industry and government requirements. For government systems, this allows Security Levels 1, 2, 3, or 4 for use on Red Hat Enterprise Linux.
See http://csrc.nist.gov/publications/PubsFIPS.html for more information.

contains 2 rules

#### Install the dracut-fips Package [ref]rule

To enable FIPS, the system requires that the `dracut-fips` package be installed. The `dracut-fips` package can be installed with the following command:

    $ sudo yum install dracut-fips

Rationale:

Use of weak or untested encryption algorithms undermines the purposes of utilizing encryption to protect data. The operating system must implement cryptographic modules adhering to the higher standards approved by the federal government since this provides assurance they have been tested and validated.

Severity: medium

Identifiers: CCE-80358-5

References: AC-17(2), 68, 2450, RHEL-07-TBD, SRG-OS-000033-GPOS-00014, SRG-OS-000396-GPOS-00176, SRG-OS-000478-GPOS-00223

#### Enable FIPS Mode in GRUB2 [ref]rule

To ensure FIPS mode is enabled, rebuild `initramfs` by running the following command:

    dracut -f

After the `dracut` command has been run, add the argument `fips=1` to the default GRUB 2 command line for the Linux operating system in `/etc/default/grub`, in the manner below:

    GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=VolGroup/LogVol06 rd.lvm.lv=VolGroup/lv_swap rhgb quiet rd.shell=0 fips=1"

Finally, rebuild the `grub.cfg` file by using the

    grub2-mkconfig -o

command as follows:

- On BIOS-based machines, issue the following command as `root`:

      ~]# grub2-mkconfig -o /boot/grub2/grub.cfg

- On UEFI-based machines, issue the following command as `root`:

      ~]# grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

Warning: Running

    dracut -f

will overwrite the existing initramfs file.
Warning: The system needs to be rebooted for these changes to take effect.
Warning: The ability to enable FIPS does not denote FIPS compliancy or certification. Red Hat, Inc. and Red Hat Enterprise Linux are respectively FIPS certified and compliant. Community projects such as CentOS, Scientific Linux, etc. do not necessarily meet FIPS certification and compliancy. Therefore, non-certified vendors and/or projects do not meet this requirement even if technically feasible.
See http://csrc.nist.gov/groups/STM/cmvp/documents/140-1/1401vend.htm for a list of FIPS certified vendors.
Rationale:

Use of weak or untested encryption algorithms undermines the purposes of utilizing encryption to protect data. The operating system must implement cryptographic modules adhering to the higher standards approved by the federal government since this provides assurance they have been tested and validated.

Severity: medium

Identifiers: CCE-80359-3

References: AC-17(2), 68, 2450, RHEL-07-021280, SRG-OS-000033-GPOS-00014, SRG-OS-000396-GPOS-00176, SRG-OS-000478-GPOS-00223

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    if grep --silent ^PRELINKING /etc/sysconfig/prelink ; then
            sed -i "s/^PRELINKING.*/PRELINKING=yes/g" /etc/sysconfig/prelink
    else
            echo -e "\n# Set PRELINKING to 'yes' per security requirements" >> /etc/sysconfig/prelink
            echo "PRELINKING=yes" >> /etc/sysconfig/prelink
    fi

    prelink -u -a

    dracut -f

    if [ -e /sys/firmware/efi ]; then
    	BOOT=`df /boot/efi | tail -1 | awk '{print $1 }'`
    else
    	BOOT=`df /boot | tail -1 | awk '{ print $1 }'`
    fi

    /sbin/grubby --update-kernel=ALL --args="boot=${BOOT} fips=1"

### Operating System Vendor Support and Certification [ref]group

The assurance of a vendor to provide operating system support and maintenance for their product is an important criterion to ensure product stability and security over the life of the product. A certified product that follows the necessary standards and government certification requirements guarantees that known software vulnerabilities will be remediated, and proper guidance for protecting and securing the operating system will be given.

contains 1 rule

#### The Installed Operating System Is Vendor Supported and Certified [ref]rule

The installed operating system must be maintained and certified by a vendor. Red Hat Enterprise Linux is supported by Red Hat, Inc. As the Red Hat Enterprise Linux vendor, Red Hat, Inc. is responsible for providing security patches as well as meeting and maintaining goverment certifications and standards.

Rationale:

An operating system is considered "supported" if the vendor continues to provide security patches for the product as well as maintain government certification requirements. With an unsupported release, it will not be possible to resolve security issue discovered in the system software as well as meet government certifications.

Severity: high

Identifiers: CCE-80349-4

References: SI-2(c), 366, RHEL-07-020240, SRG-OS-000480-GPOS-00227

#### Disable Prelinking [ref]rule

The prelinking feature changes binaries in an attempt to decrease their startup time. In order to disable it, change or add the following line inside the file `/etc/sysconfig/prelink`:

    PRELINKING=no

Next, run the following command to return binaries to a normal, non-prelinked state:

    $ sudo /usr/sbin/prelink -ua

Rationale:

Because the prelinking feature changes binaries, it can interfere with the operation of certain software and/or modes such as AIDE, FIPS, etc.

Severity: low

Identifiers: CCE-27078-5

References: CM-6(d), CM-6(3), SC-28, SI-7, Req-11.5

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    #
    # Disable prelinking altogether
    #
    if grep -q ^PRELINKING /etc/sysconfig/prelink
    then
      sed -i 's/PRELINKING.*/PRELINKING=no/g' /etc/sysconfig/prelink
    else
      echo -e "\n# Set PRELINKING=no per security requirements" >> /etc/sysconfig/prelink
      echo "PRELINKING=no" >> /etc/sysconfig/prelink
    fi

    #
    # Undo previous prelink changes to binaries
    #
    /usr/sbin/prelink -ua

### GNOME Desktop Environment [ref]group

GNOME is a graphical desktop environment bundled with many Linux distributions that allow users to easily interact with the operating system graphically rather than textually. The GNOME Graphical Display Manager (GDM) provides login, logout, and user switching contexts as well as display server management.
GNOME is developed by the GNOME Project and is considered the default Red Hat Graphical environment.
For more information on GNOME and the GNOME Project, see https://www.gnome.org

contains 24 rules

### Configure GNOME Login Screen [ref]group

In the default GNOME3 desktop, the login is displayed after system boot and can display user accounts, allow users to reboot the system, and allow users to login automatically and/or with a guest account. The login screen should be configured to prevent such behavior.
For more information about enforcing preferences in the GNOME3 environment using the DConf configuration system, see https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Desktop_Migration_and_Administration_Guide/index.html and the man page `dconf(1)`.

contains 6 rules

#### Disable GDM Automatic Login [ref]rule

The GNOME Display Manager (GDM) can allow users to automatically login without user interaction or credentials. User should always be required to authenticate themselves to the system that they are authorized to use. To disable user ability to automatically login to the system, set the `AutomaticLoginEnable` to `false` in the `[daemon]` section in `/etc/gdm/custom.conf`. For example:

    [daemon]
    AutomaticLoginEnable=false

Rationale:

Failure to restrict system access to authenticated users negatively impacts operating system security.

Severity: high

Identifiers: CCE-80104-3

References: CM-6(b), 366, SRG-OS-000480-GPOS-00229, RHEL-07-010430

#### Disable GDM Guest Login [ref]rule

The GNOME Display Manager (GDM) can allow users to login without credentials which can be useful for public kiosk scenarios. Allowing users to login without credentials or "guest" account access has inherent security risks and should be disabled. To do disable timed logins or guest account access, set the `TimedLoginEnable` to `false` in the `[daemon]` section in `/etc/gdm/custom.conf`. For example:

    [daemon]
    TimedLoginEnable=false

Rationale:

Failure to restrict system access to authenticated users negatively impacts operating system security.

Severity: high

Identifiers: CCE-80105-0

References: CM-6(b), 366, SRG-OS-000480-GPOS-00229, RHEL-07-010431

#### Disable the GNOME3 Login User List [ref]rule

In the default graphical environment, users logging directly into the system are greeted with a login screen that displays all known users. This functionality should be disabled by setting `disable-user-list` to `true`.
To disable, add or edit `disable-user-list` to `/etc/dconf/db/gdm.d/00-security-settings`. For example:

    [org/gnome/login-screen]
    disable-user-list=true

Once the setting has been added, add a lock to `/etc/dconf/db/gdm.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/login-screen/disable-user-list

After the settings have been set, run `dconf update`. Rationale:

Leaving the user list enabled is a security risk since it allows anyone with physical access to the system to quickly enumerate known user accounts without logging in.

Severity: medium

Identifiers: CCE-80106-8

References: AC-23

#### Disable the GNOME3 Login Restart and Shutdown Buttons [ref]rule

In the default graphical environment, users logging directly into the system are greeted with a login screen that allows any user, known or unknown, the ability the ability to shutdown or restart the system. This functionality should be disabled by setting `disable-restart-buttons` to `true`.
To disable, add or edit `disable-restart-buttons` to `/etc/dconf/db/gdm.d/00-security-settings`. For example:

    [org/gnome/login-screen]
    disable-restart-buttons=true

Once the setting has been added, add a lock to `/etc/dconf/db/gdm.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/login-screen/disable-restart-buttons

After the settings have been set, run `dconf update`. Rationale:

A user who is at the console can reboot the system at the login screen. If restart or shutdown buttons are pressed at the login screen, this can create the risk of short-term loss of availability of systems due to reboot.

Severity: high

Identifiers: CCE-80107-6

References: AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-TBD

#### Enable the GNOME3 Login Smartcard Authentication [ref]rule

In the default graphical environment, smart card authentication can be enabled on the login screen by setting `enable-smartcard-authentication` to `true`.
To enable, add or edit `enable-smartcard-authentication` to `/etc/dconf/db/gdm.d/00-security-settings`. For example:

    [org/gnome/login-screen]
    enable-smartcard-authentication=true

Once the setting has been added, add a lock to `/etc/dconf/db/gdm.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/login-screen/enable-smartcard-authentication

After the settings have been set, run `dconf update`. Rationale:

Smart card login provides two-factor authentication stronger than that provided by a username and password combination. Smart cards leverage PKI (public key infrastructure) in order to provide and verify credentials.

Severity: medium

Identifiers: CCE-80108-4

References: 765, 766, 767, 768, 771, 772, 884, Req-8.3

#### Set the GNOME3 Login Number of Failures [ref]rule

In the default graphical environment, the GNOME3 login screen and be configured to restart the authentication process after a configured number of attempts. This can be configured by setting `allowed-failures` to `3` or less.
To enable, add or edit `allowed-failures` to `/etc/dconf/db/gdm.d/00-security-settings`. For example:

    [org/gnome/login-screen]
    allowed-failures=3

Once the setting has been added, add a lock to `/etc/dconf/db/gdm.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/login-screen/allowed-failures

After the settings have been set, run `dconf update`. Rationale:

Setting the password retry prompts that are permitted on a per-session basis to a low value requires some software, such as SSH, to re-connect. This can slow down and draw additional attention to some types of password-guessing attacks.

Severity: medium

Identifiers: CCE-80109-2

### Configure GNOME Screen Locking [ref]group

In the default GNOME3 desktop, the screen can be locked by selecting the user name in the far right corner of the main panel and selecting Lock.
The following sections detail commands to enforce idle activation of the screensaver, screen locking, a blank-screen screensaver, and an idle activation time.
Because users should be trained to lock the screen when they step away from the computer, the automatic locking feature is only meant as a backup.
The root account can be screen-locked; however, the root account should never be used to log into an X Windows environment and should only be used to for direct login via console in emergency circumstances.
For more information about enforcing preferences in the GNOME3 environment using the DConf configuration system, see http://wiki.gnome.org/dconf and the man page `dconf(1)`. For Red Hat specific information on configuring DConf settings, see https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Desktop_Migration_and_Administration_Guide/part-Configuration_and_Administration.html

contains 7 rules

#### Set GNOME3 Screensaver Inactivity Timeout [ref]rule

The idle time-out value for inactivity in the GNOME3 desktop is configured via the `idle-delay` setting must be set under an appropriate configuration file(s) in the `/etc/dconf/db/local.d` directory and locked in `/etc/dconf/db/local.d/locks` directory to prevent user modification.
For example, to configure the system for a 15 minute delay, add the following to `/etc/dconf/db/local.d/00-security-settings`:

    [org/gnome/desktop/session]
    idle-delay=900

Once the setting has been added, add a lock to `/etc/dconf/db/local.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/desktop/session/idle-delay

After the settings have been set, run `dconf update`. Rationale:

A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not logout because of the temporary nature of the absence. Rather than relying on the user to manually lock their operating system session prior to vacating the vicinity, GNOME3 can be configured to identify when a user's session has idled and take action to initiate a session lock.

Severity: medium

Identifiers: CCE-80110-0

References: AC-11(a), 57, Req-8.1.8, SRG-OS-000029-GPOS-00010, RHEL-07-010070

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    inactivity_timeout_value="900"

    # Define constants to be reused below
    ORG_GNOME_DESKTOP_SESSION="org/gnome/desktop/session"
    SSG_DCONF_IDLE_DELAY_FILE="/etc/dconf/db/local.d/10-scap-security-guide"
    SESSION_LOCKS_FILE="/etc/dconf/db/local.d/locks/session"
    IDLE_DELAY_DEFINED="FALSE"

    # First update '[org/gnome/desktop/session] idle-delay' settings in
    # /etc/dconf/db/local.d/* if already defined
    for FILE in /etc/dconf/db/local.d/*
    do
    	if grep -q -d skip "$ORG_GNOME_DESKTOP_SESSION" "$FILE"
    	then
    		if grep 'idle-delay' "$FILE"
    		then
    			sed -i "s/idle-delay=.*/idle-delay=uint32 ${inactivity_timeout_value}/g" "$FILE"
    			IDLE_DELAY_DEFINED="TRUE"
    		fi
    	fi
    done

    # Then define '[org/gnome/desktop/session] idle-delay' setting
    # if still not defined yet
    if [ "$IDLE_DELAY_DEFINED" != "TRUE" ]
    then
    	echo "" >> $SSG_DCONF_IDLE_DELAY_FILE
    	echo "[org/gnome/desktop/session]" >>  $SSG_DCONF_IDLE_DELAY_FILE
    	echo "idle-delay=uint32 ${inactivity_timeout_value}" >> $SSG_DCONF_IDLE_DELAY_FILE
    fi

    # Verify if 'idle-delay' modification is locked. If not, lock it
    if ! grep -q "^/${ORG_GNOME_DESKTOP_SESSION}/idle-delay$" /etc/dconf/db/local.d/locks/*
    then
    	# Check if "$SESSION_LOCK_FILE" exists. If not, create it.
    	if [ ! -f "$SESSION_LOCKS_FILE" ]
    	then
    		touch "$SESSION_LOCKS_FILE"
    	fi
    	echo "/${ORG_GNOME_DESKTOP_SESSION}/idle-delay" >> "$SESSION_LOCKS_FILE"
    fi

#### Enable GNOME3 Screensaver Idle Activation [ref]rule

To activate the screensaver in the GNOME3 desktop after a period of inactivity, add or set `idle-activation-enabled` to `true` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/desktop/screensaver]
    idle_activation_enabled=true

Once the setting has been added, add a lock to `/etc/dconf/db/gdm.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/desktop/screensaver/idle-activation-enabled

After the settings have been set, run `dconf update`. Rationale:

A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not logout because of the temporary nature of the absence. Rather than relying on the user to manually lock their operating system session prior to vacating the vicinity, GNOME desktops can be configured to identify when a user's session has idled and take action to initiate the session lock. Enabling idle activation of the screensaver ensures the screensaver will be activated after the idle delay. Applications requiring continuous, real-time screen display (such as network management products) require the login session does not have administrator rights and the display station is located in a controlled-access area.

Severity: medium

Identifiers: CCE-80111-8

References: AC-11(a), 57, SRG-OS-000029-GPOS-00010, RHEL-07-010073, Req-8.1.8

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Define constants to be reused below
    ORG_GNOME_DESKTOP_SCREENSAVER="org/gnome/desktop/screensaver"
    SSG_DCONF_IDLE_ACTIVATION_FILE="/etc/dconf/db/local.d/10-scap-security-guide"
    SCREENSAVER_LOCKS_FILE="/etc/dconf/db/local.d/locks/screensaver"
    IDLE_ACTIVATION_DEFINED="FALSE"

    # First update '[org/gnome/desktop/screensaver] idle-activation-enabled' settings in
    # /etc/dconf/db/local.d/* if already defined
    for FILE in /etc/dconf/db/local.d/*
    do
    	if grep -q -d skip "$ORG_GNOME_DESKTOP_SCREENSAVER" "$FILE"
    	then
    		if grep 'idle-activation-enabled' "$FILE"
    		then
    			sed -i "s/idle-activation-enabled=.*/idle-activation-enabled=true/g" "$FILE"
    			IDLE_ACTIVATION_DEFINED="TRUE"
    		fi
    	fi
    done

    # Then define '[org/gnome/desktop/screensaver] idle-activation-enabled' setting
    # if still not defined yet
    if [ "$IDLE_ACTIVATION_DEFINED" != "TRUE" ]
    then
    	echo "" >> $SSG_DCONF_IDLE_ACTIVATION_FILE
    	echo "[org/gnome/desktop/screensaver]" >>  $SSG_DCONF_IDLE_ACTIVATION_FILE
    	echo "idle-activation-enabled=true" >> $SSG_DCONF_IDLE_ACTIVATION_FILE
    fi

    # Verify if 'idle-activation-enabled' modification is locked. If not, lock it
    if ! grep -q "^/${ORG_GNOME_DESKTOP_SCREENSAVER}/idle-activation-enabled$" /etc/dconf/db/local.d/locks/*
    then
    	# Check if "$SCREENSAVER_LOCK_FILE" exists. If not, create it.
    	if [ ! -f "$SCREENSAVER_LOCKS_FILE" ]
    	then
    		touch "$SCREENSAVER_LOCKS_FILE"
    	fi
    	echo "/${ORG_GNOME_DESKTOP_SCREENSAVER}/idle-activation-enabled" >> "$SCREENSAVER_LOCKS_FILE"
    fi

#### Enable GNOME3 Screensaver Lock After Idle Period [ref]rule

To activate locking of the screensaver in the GNOME3 desktop when it is activated, add or set `lock-enabled` to `true` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/desktop/screensaver]
    lock-enabled=true

Once the settings have been added, add a lock to `/etc/dconf/db/gdm.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/desktop/screensaver/lock-enabled

After the settings have been set, run `dconf update`. Rationale:

A session lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not want to logout because of the temporary nature of the absense.

Severity: medium

Identifiers: CCE-80112-6

References: AC-11(b), 56, Req-8.1.8, SRG-OS-000028-GPOS-00009, OS-SRG-000030-GPOS-00011, RHEL-07-010060

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Define constants to be reused below
    ORG_GNOME_DESKTOP_SCREENSAVER="org/gnome/desktop/screensaver"
    SSG_DCONF_LOCK_ENABLED_FILE="/etc/dconf/db/local.d/10-scap-security-guide"
    SCREENSAVER_LOCKS_FILE="/etc/dconf/db/local.d/locks/screensaver"
    LOCK_ENABLED_DEFINED="FALSE"
    LOCK_DELAY_DEFINED="FALSE"

    # First update '[org/gnome/desktop/screensaver] lock-enabled' and
    # '[org/gnome/desktop/screensaver] lock-delay' settings in
    # /etc/dconf/db/local.d/* if already defined
    for FILE in /etc/dconf/db/local.d/*
    do
    	if grep -q -d skip "$ORG_GNOME_DESKTOP_SCREENSAVER" "$FILE"
    	then
    		if grep 'lock-enabled' "$FILE"
    		then
    			sed -i "s/lock-enabled=.*/lock-enabled=true/g" "$FILE"
    			LOCK_ENABLED_DEFINED="TRUE"
    		fi
    		if grep 'lock-delay' "$FILE"
    		then
    			sed -i "s/lock-delay=.*/lock-delay=uint32 0/g" "$FILE"
    			LOCK_DELAY_DEFINED="TRUE"
    		fi
    	fi
    done

    # Then define '[org/gnome/desktop/screensaver] lock-enabled' setting
    # if still not defined yet
    if [ "$LOCK_ENABLED_DEFINED" != "TRUE" ] || [ "$LOCK_DELAY_DEFINED" != "TRUE" ]
    then
    	echo "" >> $SSG_DCONF_LOCK_ENABLED_FILE
    	echo "[org/gnome/desktop/screensaver]" >>  $SSG_DCONF_LOCK_ENABLED_FILE
    	echo "lock-enabled=true" >> $SSG_DCONF_LOCK_ENABLED_FILE
    	echo "lock-delay=uint32 0" >> $SSG_DCONF_LOCK_ENABLED_FILE
    fi

    # Verify if 'lock-enabled' modification is locked. If not, lock it
    if ! grep -q "^/${ORG_GNOME_DESKTOP_SCREENSAVER}/lock-enabled$" /etc/dconf/db/local.d/locks/*
    then
    	# Check if "$SCREENSAVER_LOCK_FILE" exists. If not, create it.
    	if [ ! -f "$SCREENSAVER_LOCKS_FILE" ]
    	then
    		touch "$SCREENSAVER_LOCKS_FILE"
    	fi
    	echo "/${ORG_GNOME_DESKTOP_SCREENSAVER}/lock-enabled" >> "$SCREENSAVER_LOCKS_FILE"
    fi

    # Verify if 'lock-delay' modification is locked. If not, lock it
    if ! grep -q "^/${ORG_GNOME_DESKTOP_SCREENSAVER}/lock-delay$" /etc/dconf/db/local.d/locks/*
    then
            # Check if "$SCREENSAVER_LOCK_FILE" exists. If not, create it.
            if [ ! -f "$SCREENSAVER_LOCKS_FILE" ]
            then
                    touch "$SCREENSAVER_LOCKS_FILE"
            fi
            echo "/${ORG_GNOME_DESKTOP_SCREENSAVER}/lock-delay" >> "$SCREENSAVER_LOCKS_FILE"
    fi

#### Set GNOME3 Screensaver Lock Delay After Activation Period [ref]rule

To activate the locking delay of the screensaver in the GNOME3 desktop when the screensaver is activated, add or set `lock-delay` to `uint32 0` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/desktop/screensaver]
    lock-delay=uint32 0

Once the setting has been added, add a lock to `/etc/dconf/db/gdm.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/desktop/screensaver/lock-delay

After the settings have been set, run `dconf update`. Rationale:

A session lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not want to logout because of the temporary nature of the absense.

Severity: medium

Identifiers: CCE-80370-0

References: AC-11(a), 56, Req-8.1.8, OS-SRG-000029-GPOS-00010, RHEL-07-010074

#### Implement Blank Screensaver [ref]rule

To set the screensaver mode in the GNOME3 desktop to a blank screen, add or set `picture-uri` to `''` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/desktop/screensaver]
    picture-uri=''

Once the settings have been added, add a lock to `/etc/dconf/db/gdm.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/desktop/screensaver/picture-uri

After the settings have been set, run `dconf update`. Rationale:

Setting the screensaver mode to blank-only conceals the contents of the display from passersby.

Severity: low

Identifiers: CCE-80113-4

References: AC-11(b), 60, Req-8.1.8

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Define constants to be reused below
    ORG_GNOME_DESKTOP_SCREENSAVER="org/gnome/desktop/screensaver"
    SSG_DCONF_MODE_BLANK_FILE="/etc/dconf/db/local.d/10-scap-security-guide"
    SCREENSAVER_LOCKS_FILE="/etc/dconf/db/local.d/locks/screensaver"
    MODE_BLANK_DEFINED="FALSE"

    # First update '[org/gnome/desktop/screensaver] picture-uri' settings in
    # /etc/dconf/db/local.d/* if already defined
    for FILE in /etc/dconf/db/local.d/*
    do
    	if grep -q -d skip "$ORG_GNOME_DESKTOP_SCREENSAVER" "$FILE"
    	then
    		if grep 'picture-uri' "$FILE"
    		then
    			sed -i "s/picture-uri=.*/picture-uri=string ''/g" "$FILE"
    			MODE_BLANK_DEFINED="TRUE"
    		fi
    	fi
    done

    # Then define '[org/gnome/desktop/screensaver] picture-uri' setting
    # if still not defined yet
    if [ "$MODE_BLANK_DEFINED" != "TRUE" ]
    then
    	echo "" >> $SSG_DCONF_MODE_BLANK_FILE
    	echo "[org/gnome/desktop/screensaver]" >>  $SSG_DCONF_MODE_BLANK_FILE
    	echo "picture-uri=string ''" >> $SSG_DCONF_MODE_BLANK_FILE
    fi

    # Verify if 'picture-uri' modification is locked. If not, lock it
    if ! grep -q "^/${ORG_GNOME_DESKTOP_SCREENSAVER}/picture-uri$" /etc/dconf/db/local.d/locks/*
    then
    	# Check if "$SCREENSAVER_LOCK_FILE" exists. If not, create it.
    	if [ ! -f "$SCREENSAVER_LOCKS_FILE" ]
    	then
    		touch "$SCREENSAVER_LOCKS_FILE"
    	fi
    	echo "/${ORG_GNOME_DESKTOP_SCREENSAVER}/picture-uri" >> "$SCREENSAVER_LOCKS_FILE"
    fi

#### Disable Full User Name on Splash Shield [ref]rule

By default when the screen is locked, the splash shield will show the user's full name. This should be disabled to prevent casual observers from seeing who has access to the system. This can be disabled by adding or setting `show-full-name-in-top-bar` to `false` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/desktop/screensaver]
    show-full-name-in-top-bar=false

Once the settings have been added, add a lock to `/etc/dconf/db/gdm.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/desktop/screensaver/show-full-name-in-top-bar

After the settings have been set, run `dconf update`. Rationale:

Setting the splash screen to not reveal the logged in user's name conceals who has access to the system from passersby.

Severity: low

Identifiers: CCE-80114-2

#### Ensure Users Cannot Change GNOME3 Session Settings [ref]rule

If not already configured, ensure that users cannot change GNOME3 session idle and lock settings by adding `/org/gnome/desktop/screensaver/lock-delay` and `/org/gnome/desktop/session/idle-delay` to `/etc/dconf/db/gdm.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/desktop/screensaver/lock-delay
    /org/gnome/desktop/session/idle-delay

After the settings have been set, run `dconf update`. Rationale:

A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but does not logout because of the temporary nature of the absence. Rather than relying on the user to manually lock their operating system session prior to vacating the vicinity, GNOME desktops can be configured to identify when a user's session has idled and take action to initiate the session lock. As such, users should not be allowed to change session settings.

Severity: low

Identifiers: CCE-80371-8

References: AC-11(a), 57, SRG-OS-00029-GPOS-0010, RHEL-07-010071

### GNOME System Settings [ref]group

GNOME provides configuration and functionality to a graphical desktop environment that changes grahical configurations or allow a user to perform actions that users normally would not be able to do in non-graphical mode such as remote access configuration, power policies, Geo-location, etc. Configuring such settings in GNOME will prevent accidential graphical configuration changes by users from taking place.

contains 4 rules

#### Disable Ctrl-Alt-Del Reboot Key Sequence in GNOME3 [ref]rule

By default, `GNOME` will reboot the system if the `Ctrl-Alt-Del` key sequence is pressed.
To configure the system to ignore the `Ctrl-Alt-Del` key sequence from the Graphical User Interface (GUI) instead of rebooting the system, add or set `logout` to `''` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/settings-daemon/plugins/media-keys]
    logout=''

Once the settings have been added, add a lock to `/etc/dconf/db/local.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/settings-daemon/plugins/media-keys/logout

After the settings have been set, run `dconf update`. Rationale:

A locally logged-in user who presses Ctrl-Alt-Del, when at the console, can reboot the system. If accidentally pressed, as could happen in the case of mixed OS environment, this can create the risk of short-term loss of availability of systems due to unintentional reboot.

Severity: high

Identifiers: CCE-80124-1

References: AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-TBD

#### Disable User Administration in GNOME3 [ref]rule

By default, `GNOME` will allow all users to have some administratrion capability. This should be disabled so that non-administrative users are not making configuration changes. To configure the system to disable user administration capability in the Graphical User Interface (GUI), add or set `user-administration-disabled` to `true` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/desktop/lockdown]
    user-administration-disabled=true

Once the settings have been added, add a lock to `/etc/dconf/db/local.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/desktop/lockdown/user-administration-disabled

After the settings have been set, run `dconf update`. Rationale:

Allowing all users to have some administratrive capabilities to the system through the Graphical User Interface (GUI) when they would not have them otherwise could allow unintended configuration changes as well as a nefarious user the capability to make system changes such as adding new accounts, etc.

Severity: high

Identifiers: CCE-80115-9

#### Disable Power Settings in GNOME3 [ref]rule

By default, `GNOME` enables a power profile designed for mobile devices with battery usage. While useful for mobile devices, this setting should be disabled for all other systems. To configure the system to disable the power setting, add or set `active` to `false` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/settings-daemon/plugins/power]
    active=false

Once the settings have been added, add a lock to `/etc/dconf/db/local.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/settings-daemon/plugins/power

After the settings have been set, run `dconf update`. Rationale:

Power settings should not be enabled on systems that are not mobile devices. Enabling power settings on non-mobile devices could have unintended processing consequences on standard systems.

Severity: medium

Identifiers: CCE-80116-7

#### Disable Geolocation in GNOME3 [ref]rule

`GNOME` allows the clock and applications to track and access location information. This setting should be disabled as applications should not track system location. To configure the system to disable location tracking, add or set `enabled` to `false` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/system/location]
    enabled=false

To configure the clock to disable location tracking, add or set `geolocation` to `false` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/clocks]
    geolocation=false

Once the settings have been added, add a lock to `/etc/dconf/db/local.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/system/location/enabled
    /org/gnome/clocks/geolocation

After the settings have been set, run `dconf update`. Rationale:

Power settings should not be enabled on systems that are not mobile devices. Enabling power settings on non-mobile devices could have unintended processing consequences on standard systems.

Severity: medium

Identifiers: CCE-80117-5

### GNOME Network Settings [ref]group

GNOME network settings that apply to the graphical interface.

contains 2 rules

#### Disable WIFI Network Connection Creation in GNOME3 [ref]rule

`GNOME` allows users to create ad-hoc wireless connections through the `NetworkManager` applet. Wireless connections should be disabled by adding or setting `disable-wifi-create` to `true` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/nm-applet]
    disable-wifi-create=true

Once the settings have been added, add a lock to `/etc/dconf/db/local.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/nm-applet/disable-wifi-create

After the settings have been set, run `dconf update`. Rationale:

Wireless network connections should not be allowed to be configured by general users on a given system as it could open the system to backdoor attacks.

Severity: medium

Identifiers: CCE-80118-3

#### Disable WIFI Network Notification in GNOME3 [ref]rule

By default, `GNOME` disables WIFI notification. This should be permanently set so that users do not connect to a wireless network when the system finds one. While useful for mobile devices, this setting should be disabled for all other systems. To configure the system to disable the WIFI notication, add or set `suppress-wireless-networks-available` to `true` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/nm-applet]
    suppress-wireless-networks-available=true

Once the settings have been added, add a lock to `/etc/dconf/db/local.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/nm-applet/suppress-wireless-networks-available

After the settings have been set, run `dconf update`. Rationale:

Wireless network connections should not be allowed to be configured by general users on a given system as it could open the system to backdoor attacks.

Severity: medium

Identifiers: CCE-80119-1

### GNOME Remote Access Settings [ref]group

GNOME remote access settings that apply to the graphical interface.

contains 2 rules

#### Require Credential Prompting for Remote Access in GNOME3 [ref]rule

By default, `GNOME` does not require credentials when using `Vino` for remote access. To configure the system to require remote credentials, add or set `authentication-methods` to `['vnc']` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/Vino]
    authentication-methods=['vnc']

Once the settings have been added, add a lock to `/etc/dconf/db/local.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/Vino/authentication-methods

After the settings have been set, run `dconf update`. Rationale:

Username and password prompting is required for remote access. Otherwise, non-authorized and nefarious users can access the system freely.

Severity: medium

Identifiers: CCE-80120-9

#### Require Encryption for Remote Access in GNOME3 [ref]rule

By default, `GNOME` requires encryption when using `Vino` for remote access. To prevent remote access encryption from being disabled, add or set `require-encryption` to `true` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/Vino]
    require-encryption=true

Once the settings have been added, add a lock to `/etc/dconf/db/local.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/Vino/require-encryption

After the settings have been set, run `dconf update`. Rationale:

Open X displays allow an attacker to capture keystrokes and to execute commands remotely.

Severity: medium

Identifiers: CCE-80121-7

References: CM-2(1)(b), 366, SRG-OS-000480-GPOS-00227, RHEL-07-TBD

### GNOME Media Settings [ref]group

GNOME media settings that apply to the graphical interface.

contains 2 rules

#### Disable GNOME3 Automounting [ref]rule

The system's default desktop environment, GNOME3, will mount devices and removable media (such as DVDs, CDs and USB flash drives) whenever they are inserted into the system. To disable automount and autorun within GNOME3, add or set `automount` to `false`, `automount-open` to `false`, and `autorun-never` to `true` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/desktop/media-handling]
    automount=false
    automount-open=false
    autorun-never=true

Once the settings have been added, add a lock to `/etc/dconf/db/local.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/desktop/media-handling/automount
    /org/gnome/desktop/media-handling/auto-open
    /org/gnome/desktop/media-handling/autorun-never

After the settings have been set, run `dconf update`. Rationale:

Disabling automatic mounting in GNOME3 can prevent the introduction of malware via removable media. It will, however, also prevent desktop users from legitimate use of removable media.

Severity: low

Identifiers: CCE-80122-5

References: AC-19(a), AC-19(d), AC-19(e)

#### Disable All GNOME3 Thumbnailers [ref]rule

The system's default desktop environment, GNOME3, uses a number of different thumbnailer programs to generate thumbnails for any new or modified content in an opened folder. To disable the execution of these thumbnail applications, add or set `disable-all` to `true` in `/etc/dconf/db/local.d/00-security-settings`. For example:

    [org/gnome/desktop/thumbnailers]
    disable-all=true

Once the settings have been added, add a lock to `/etc/dconf/db/local.d/locks/00-security-settings-lock` to prevent user modification. For example:

    /org/gnome/desktop/thumbnailers/disable-all

After the settings have been set, run `dconf update`. This effectively prevents an attacker from gaining access to a system through a flaw in GNOME3's Nautilus thumbnail creators. Rationale:

An attacker with knowledge of a flaw in a GNOME3 thumbnailer application could craft a malicious file to exploit this flaw. Assuming the attacker could place the malicious file on the local filesystem (via a web upload for example) and assuming a user browses the same location using Nautilus, the malicious file would exploit the thumbnailer with the potential for malicious code execution. It is best to disable these thumbnailer applications unless they are explicitly required.

Severity: low

Identifiers: CCE-80123-3

References: CM-7

#### Configure GNOME3 DConf User Profile [ref]rule

By default, DConf provides a standard user profile. This profile contains a list of DConf configuration databases. The user profile and database always take the highest priority. As such the DConf User profile should always exist and be configured correctly.
To make sure that the user profile is configured correctly, the `/etc/dconf/profile/user` should be set as follows:

    user-db:user
    system-db:local
    system-db:site
    system-db:distro

Rationale:

Failure to have a functional DConf profile prevents GNOME3 configuration settings from being enforced for all users and allows various security risks.

Severity: high

Identifiers: CCE-27446-4

### Sudo [ref]group

`Sudo`, which stands for "su 'do'", provides the ability to delegate authority to certain users, groups of users, or system administrators. When configured for system users and/or groups, `Sudo` can allow a user or group to execute privileged commands that normally only `root` is allowed to execute.
For more information on `Sudo` and addition `Sudo` configuration options, see https://www.sudo.ws

contains 2 rules

#### Ensure Users Re-Authenticate for Privilege Escalation - sudo NOPASSWD [ref]rule

The sudo `NOPASSWD` tag, when specified, allows a user to execute commands using sudo without having to authenticate. This should be disabled by making sure that the `NOPASSWD` tag does not exist in `/etc/sudoers` configuration file or any sudo configuration snippets in `/etc/sudoers.d/`.

Rationale:

Without re-authentication, users may access resources or perform tasks for which they do not have authorization.
When operating systems provide the capability to escalate a functional capability, it is critical that the user re-authenticate.

Severity: medium

Identifiers: CCE-80351-0

References: IA-11, 2038, RHEL-07-010380, SRG-OS-000373-GPOS-00156, SRG-OS-000373-GPOS-00157, SRG-OS-000373-GPOS-00158

#### Ensure Users Re-Authenticate for Privilege Escalation - sudo !authenticate [ref]rule

The sudo `!authenticate` option, when specified, allows a user to execute commands using sudo without having to authenticate. This should be disabled by making sure that the `!authenticate` option does not exist in `/etc/sudoers` configuration file or any sudo configuration snippets in `/etc/sudoers.d/`.

Rationale:

Without re-authentication, users may access resources or perform tasks for which they do not have authorization.
When operating systems provide the capability to escalate a functional capability, it is critical that the user re-authenticate.

Severity: medium

Identifiers: CCE-80350-2

References: IA-11, 2038, RHEL-07-010381, SRG-OS-000373-GPOS-00156, SRG-OS-000373-GPOS-00157, SRG-OS-000373-GPOS-00158

### File Permissions and Masks [ref]group

Traditional Unix security relies heavily on file and directory permissions to prevent unauthorized users from reading or modifying files to which they should not have access.
Several of the commands in this section search filesystems for files or directories with certain characteristics, and are intended to be run on every local partition on a given system. When the variable PART appears in one of the commands below, it means that the command is intended to be run repeatedly, with the name of each local partition substituted for PART in turn.
The following command prints a list of all xfs partitions on the local system, which is the default filesystem for Red Hat Enterprise Linux 7 installations:

    $ mount -t xfs | awk '{print $3}'

For any systems that use a different local filesystem type, modify this command as appropriate.

contains 17 rules

### Restrict Partition Mount Options [ref]group

System partitions can be mounted with certain options that limit what files on those partitions can do. These options are set in the `/etc/fstab` configuration file, and can be used to make certain types of malicious behavior more difficult.

contains 3 rules

#### Add nodev Option to Removable Media Partitions [ref]rule

The `nodev` mount option prevents files from being interpreted as character or block devices. Legitimate character and block devices should exist only in the `/dev` directory on the root partition or within chroot jails built for system services. Add the `nodev` option to the fourth column of `/etc/fstab` for the line which controls mounting of any removable media partitions.

Rationale:

The only legitimate location for device files is the `/dev` directory located on the root partition. An exception to this is chroot jails, and it is not advised to set `nodev` on partitions which contain their root filesystems.

Severity: low

Identifiers: CCE-80146-4

References: AC-19(a), AC-19(d), AC-19(e), CM-7, MP-2

#### Add noexec Option to Removable Media Partitions [ref]rule

The `noexec` mount option prevents the direct execution of binaries on the mounted filesystem. Preventing the direct execution of binaries from removable media (such as a USB key) provides a defense against malicious software that may be present on such untrusted media. Add the `noexec` option to the fourth column of `/etc/fstab` for the line which controls mounting of any removable media partitions.

Rationale:

Allowing users to execute binaries from removable media such as USB keys exposes the system to potential compromise.

Severity: low

Identifiers: CCE-80147-2

References: AC-19(a), AC-19(d), AC-19(e), CM-7, MP-2, 87, 1.1.12

#### Add nosuid Option to Removable Media Partitions [ref]rule

The `nosuid` mount option prevents set-user-identifier (SUID) and set-group-identifier (SGID) permissions from taking effect. These permissions allow users to execute binaries with the same permissions as the owner and group of the file respectively. Users should not be allowed to introduce SUID and SGID files into the system via partitions mounted from removeable media. Add the `nosuid` option to the fourth column of `/etc/fstab` for the line which controls mounting of any removable media partitions.

Rationale:

The presence of SUID and SGID executables should be tightly controlled. Allowing users to introduce SUID or SGID binaries from partitions mounted off of removable media would allow them to introduce their own highly-privileged programs.

Severity: low

Identifiers: CCE-80148-0

References: AC-6, AC-19(a), AC-19(d), AC-19(e), CM-7, MP-2, 1.1.13, 366, SRG-OS-000480-GPOS-00227, RHEL-07-021011

### Restrict Dynamic Mounting and Unmounting of Filesystems [ref]group

Linux includes a number of facilities for the automated addition and removal of filesystems on a running system. These facilities may be necessary in many environments, but this capability also carries some risk -- whether direct risk from allowing users to introduce arbitrary filesystems, or risk that software flaws in the automated mount facility itself could allow an attacker to compromise the system.
This command can be used to list the types of filesystems that are available to the currently executing kernel:

    $ find /lib/modules/`uname -r`/kernel/fs -type f -name '*.ko'

If these filesystems are not required then they can be explicitly disabled in a configuratio file in `/etc/modprobe.d`.

contains 5 rules

#### Disable Modprobe Loading of USB Storage Driver [ref]rule

To prevent USB storage devices from being used, configure the kernel module loading system to prevent automatic loading of the USB storage driver. To configure the system to prevent the `usb-storage` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install usb-storage /bin/true

This will prevent the `modprobe` program from loading the `usb-storage` module, but will not prevent an administrator (or another program) from using the `insmod` program to load the module manually.Rationale:

USB storage devices such as thumb drives can be used to introduce malicious software.

Severity: medium

Identifiers: CCE-27277-3

References: AC-19(a), AC-19(d), AC-19(e), IA-3, 366, 778, 1958, SRG-OS-000114-GPOS-00059, SRG-OS-000378-GPOS-0016, SRG-OS-000480-GPOS-00227, RHEL-07-020160

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    if grep --silent "^install usb-storage" /etc/modprobe.d/usb-storage.conf ; then
            sed -i 's/^install usb-storage.*/install usb-storage /bin/true/g' /etc/modprobe.d/usb-storage.conf
    else
            echo -e "\n# Disable per security requirements" >> /etc/modprobe.d/usb-storage.conf
            echo "install usb-storage /bin/true" >> /etc/modprobe.d/usb-storage.conf
    fi

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    - name: Ensure kernel module 'usb-storage' is disabled
      lineinfile:
        create=yes
        dest="/etc/modprobe.d/{{item}}.conf"
        regexp="{{item}}"
        line="install {{item}} /bin/true"
      with_items:
        - usb-storage

#### Disable Kernel Support for USB via Bootloader Configuration [ref]rule

All USB support can be disabled by adding the `nousb` argument to the kernel's boot loader configuration. To do so, append "nousb" to the kernel line in `/etc/default/grub` as shown:

    kernel /vmlinuz-VERSION ro vga=ext root=/dev/VolGroup00/LogVol00 rhgb quiet nousb

WARNING: Disabling all kernel support for USB will cause problems for systems with USB-based keyboards, mice, or printers. This configuration is infeasible for systems which require USB devices, which is common.Rationale:

Disabling the USB subsystem within the Linux kernel at system boot will protect against potentially malicious USB devices, although it is only practical in specialized systems.

Severity: low

Identifiers: CCE-26548-8

References: AC-19(a), AC-19(d), AC-19(e), 1250

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Correct the form of default kernel command line in /etc/default/grub
    if ! grep -q ^GRUB_CMDLINE_LINUX=\".*nousb.*\" /etc/default/grub;
    then
      # Edit configuration setting
      # Append 'nousb' argument to /etc/default/grub (if not present yet)
      sed -i "s/\(GRUB_CMDLINE_LINUX=\)\"\(.*\)\"/\1\"\2 nousb\"/" /etc/default/grub
      # Edit runtime setting
      # Correct the form of kernel command line for each installed kernel in the bootloader
      /sbin/grubby --update-kernel=ALL --args="nousb"
    fi

#### Disable Booting from USB Devices in Boot Firmware [ref]rule

Configure the system boot firmware (historically called BIOS on PC systems) to disallow booting from USB drives.

Rationale:

Booting a system from a USB device would allow an attacker to circumvent any security measures provided by the operating system. Attackers could mount partitions and modify the configuration of the OS.

Severity: low

Identifiers: CCE-26960-5

References: AC-19(a), AC-19(d), AC-19(e), 1250

#### Assign Password to Prevent Changes to Boot Firmware Configuration [ref]rule

Assign a password to the system boot firmware (historically called BIOS on PC systems) to require a password for any configuration changes.

Rationale:

Assigning a password to the system boot firmware prevents anyone with physical access from configuring the system to boot from local media and circumvent the operating system's access controls. For systems in physically secure locations, such as a data center or Sensitive Compartmented Information Facility (SCIF), this risk must be weighed against the risk of administrative personnel being unable to conduct recovery operations in a timely fashion.

Severity: low

Identifiers: CCE-27194-0

#### Disable the Automounter [ref]rule

The `autofs` daemon mounts and unmounts filesystems, such as user home directories shared via NFS, on demand. In addition, autofs can be used to handle removable media, and the default configuration provides the cdrom device as `/misc/cd`. However, this method of providing access to removable media is not common, so autofs can almost always be disabled if NFS is not in use. Even if NFS is required, it may be possible to configure filesystem mounts statically by editing `/etc/fstab` rather than relying on the automounter.
The `autofs` service can be disabled with the following command:

    $ sudo systemctl disable autofs.service

Rationale:

Disabling the automounter permits the administrator to statically control filesystem mounting through `/etc/fstab`.
Additionally, automatically mounting filesystems permits easy introduction of unknown devices, thereby facilitating malicious activity.

Severity: medium

Identifiers: CCE-27498-5

References: AC-19(a), AC-19(d), AC-19(e), IA-3, 366, 778, 1958, SRG-OS-000114-GPOS-00059, SRG-OS-000378-GPOS-00163, SRG-OS-000480-GPOS-00227, RHEL-07-020161

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

    service_command disable autofs

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Disable service autofs
      service:
        name="{{item}}"
        enabled="no"
        state="stopped"
      with_items:
        - autofs

### Verify Permissions on Important Files and Directories [ref]group

Permissions for many files on a system must be set restrictively to ensure sensitive information is properly protected. This section discusses important permission restrictions which can be verified to ensure that no harmful discrepancies have arisen.

contains 3 rules

#### Ensure All Files Are Owned by a User [ref]rule

If any files are not owned by a user, then the cause of their lack of ownership should be investigated. Following this, the files should be deleted or assigned to an appropriate user.

Rationale:

Unowned files do not directly imply a security problem, but they are generally a sign that something is amiss. They may be caused by an intruder, by incorrect software installation or draft software removal, or by failure to remove all files belonging to a deleted account. The files should be repaired so they will not cause problems when accounts are created in the future, and the cause should be discovered and addressed.

Severity: medium

Identifiers: CCE-80134-0

References: AC-3(4), AC-6, CM-6(b), 002165, SRG-OS-000480-GPOS-00227, RHEL-07-020360

#### Ensure All Files Are Owned by a Group [ref]rule

If any files are not owned by a group, then the cause of their lack of group-ownership should be investigated. Following this, the files should be deleted or assigned to an appropriate group.

Rationale:

Unowned files do not directly imply a security problem, but they are generally a sign that something is amiss. They may be caused by an intruder, by incorrect software installation or draft software removal, or by failure to remove all files belonging to a deleted account. The files should be repaired so they will not cause problems when accounts are created in the future, and the cause should be discovered and addressed.

Severity: medium

Identifiers: CCE-80135-7

References: AC-3(4), AC-6, IA-2, 02165, SRG-OS-000480-GPOS-00227, RHEL-07-020370

#### Ensure All World-Writable Directories Are Owned by a System Account [ref]rule

All directories in local partitions which are world-writable should be owned by root or another system account. If any world-writable directories are not owned by a system account, this should be investigated. Following this, the files should be deleted or assigned to an appropriate group.

Rationale:

Allowing a user account to own a world-writable directory is undesirable because it allows the owner of that directory to remove or replace any files that may be placed in the directory by other users.

Severity: low

Identifiers: CCE-80136-5

References: AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-021050

### Restrict Programs from Dangerous Execution Patterns [ref]group

The recommendations in this section are designed to ensure that the system's features to protect against potentially dangerous program execution are activated. These protections are applied at the system initialization or kernel level, and defend against certain types of badly-configured or compromised programs.

contains 6 rules

### Disable Core Dumps [ref]group

A core dump file is the memory image of an executable program when it was terminated by the operating system due to errant behavior. In most cases, only software developers legitimately need to access these files. The core dump files may also contain sensitive information, or unnecessarily occupy large amounts of disk space.
Once a hard limit is set in `/etc/security/limits.conf`, a user cannot increase that limit within his or her own session. If access to core dumps is required, consider restricting them to only certain users or groups. See the `limits.conf` man page for more information.
The core dumps of setuid programs are further protected. The `sysctl` variable `fs.suid_dumpable` controls whether the kernel allows core dumps from these programs at all. The default value of 0 is recommended.

contains 1 rule

#### Disable Core Dumps for SUID programs [ref]rule

To set the runtime status of the `fs.suid_dumpable` kernel parameter, run the following command:

    $ sudo sysctl -w fs.suid_dumpable=0

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    fs.suid_dumpable = 0

Rationale:

The core dump of a setuid program is more likely to contain sensitive data, as the program itself runs with greater privileges than the user who initiated execution of the program. Disabling the ability for any setuid program to write a core file decreases the risk of unauthorized access of such data.

Severity: low

Identifiers: CCE-26900-1

References: SI-11, 1.6.1

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    #
    # Set runtime for fs.suid_dumpable
    #
    /sbin/sysctl -q -n -w fs.suid_dumpable=0

    #
    # If fs.suid_dumpable present in /etc/sysctl.conf, change value to "0"
    #	else, add "fs.suid_dumpable = 0" to /etc/sysctl.conf
    #
    if grep --silent ^fs.suid_dumpable /etc/sysctl.conf ; then
    	sed -i 's/^fs.suid_dumpable.*/fs.suid_dumpable = 0/g' /etc/sysctl.conf
    else
    	echo -e "\n# Set fs.suid_dumpable to 0 per security requirements" >> /etc/sysctl.conf
    	echo "fs.suid_dumpable = 0" >> /etc/sysctl.conf
    fi

### Enable ExecShield [ref]group

ExecShield describes kernel features that provide protection against exploitation of memory corruption errors such as buffer overflows. These features include random placement of the stack and other memory regions, prevention of execution in memory that should only hold data, and special handling of text buffers. These protections are enabled by default on 32-bit systems and controlled through `sysctl` variables `kernel.exec-shield` and `kernel.randomize_va_space`. On the latest 64-bit systems, `kernel.exec-shield` cannot be enabled or disabled with `sysctl`.

contains 2 rules

#### Enable ExecShield [ref]rule

By default on Red Hat Enterprise Linux 7 64-bit systems, ExecShield is enabled and can only be disabled if the hardware does not support ExecShield or is disabled in `/etc/default/grub`. For Red Hat Enterprise Linux 7 32-bit systems, `sysctl` can be used to enable ExecShield.

Rationale:

ExecShield uses the segmentation feature on all x86 systems to prevent execution in memory higher than a certain address. It writes an address as a limit in the code segment descriptor, to control where code can be executed, on a per-process basis. When the kernel places a process's memory regions such as the stack and heap higher than this address, the hardware prevents execution in that address range. This is enabled by default on the latest Red Hat and Fedora systems if supported by the hardware.

Severity: medium

Identifiers: CCE-27211-2

References: SC-39, 2530

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    if [ $(getconf LONG_BIT) = "32" ] ; then
      #
      # Set runtime for kernel.exec-shield
      #
      sysctl -q -n -w kernel.exec-shield=1

      #
      # If kernel.exec-shield present in /etc/sysctl.conf, change value to "1"
      #	else, add "kernel.exec-shield = 1" to /etc/sysctl.conf
      #
      if grep --silent ^kernel.exec-shield /etc/sysctl.conf ; then
    	sed -i 's/^kernel.exec-shield.*/kernel.exec-shield = 1/g' /etc/sysctl.conf
      else
    	echo -e "\n# Set kernel.exec-shield to 1 per security requirements" >> /etc/sysctl.conf
    	echo "kernel.exec-shield = 1" >> /etc/sysctl.d/sysctl.conf
      fi
    fi

    if [ $(getconf LONG_BIT) = "64" ] ; then
      if grep --silent noexec /boot/grub2/grub*.cfg ; then
            sed -i "s/noexec.*//g" /etc/default/grub
            sed -i "s/noexec.*//g" /etc/grub.d/*
            GRUBCFG=`ls | grep '.cfg$'`
            grub2-mkconfig -o /boot/grub2/$GRUBCFG
      fi
    fi

#### Enable Randomized Layout of Virtual Address Space [ref]rule

To set the runtime status of the `kernel.randomize_va_space` kernel parameter, run the following command:

    $ sudo sysctl -w kernel.randomize_va_space=2

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    kernel.randomize_va_space = 2

Rationale:

Address space layout randomization (ASLR) makes it more difficult for an attacker to predict the location of attack code they have introduced into a process's address space during an attempt at exploitation. Additionally, ASLR makes it more difficult for an attacker to know the location of existing code in order to re-purpose it using return oriented programming (ROP) techniques.

Severity: medium

Identifiers: CCE-27127-0

References: SC-30(2), 1.6.1

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/sysctl.conf' '^kernel.randomize_va_space' '2' 'CCE-27127-0'

### Enable Execute Disable (XD) or No Execute (NX) Support on x86 Systems [ref]group

Recent processors in the x86 family support the ability to prevent code execution on a per memory page basis. Generically and on AMD processors, this ability is called No Execute (NX), while on Intel processors it is called Execute Disable (XD). This ability can help prevent exploitation of buffer overflow vulnerabilities and should be activated whenever possible. Extra steps must be taken to ensure that this protection is enabled, particularly on 32-bit x86 systems. Other processors, such as Itanium and POWER, have included such support since inception and the standard kernel for those platforms supports the feature. This is enabled by default on the latest Red Hat and Fedora systems if supported by the hardware.

contains 2 rules

#### Install PAE Kernel on Supported 32-bit x86 Systems [ref]rule

Systems that are using the 64-bit x86 kernel package do not need to install the kernel-PAE package because the 64-bit x86 kernel already includes this support. However, if the system is 32-bit and also supports the PAE and NX features as determined in the previous section, the kernel-PAE package should be installed to enable XD or NX support:

    $ sudo yum install kernel-PAE

The installation process should also have configured the bootloader to load the new kernel at boot. Verify this at reboot and modify `/etc/default/grub` if necessary.
Warning: The kernel-PAE package should not be installed on older systems that do not support the XD or NX bit, as this may prevent them from booting.
Rationale:

On 32-bit systems that support the XD or NX bit, the vendor-supplied PAE kernel is required to enable either Execute Disable (XD) or No Execute (NX) support.

Severity: low

Identifiers: CCE-27116-3

References: CM-6(b)

#### Enable NX or XD Support in the BIOS [ref]rule

Reboot the system and enter the BIOS or Setup configuration menu. Navigate the BIOS configuration menu and make sure that the option is enabled. The setting may be located under a Security section. Look for Execute Disable (XD) on Intel-based systems and No Execute (NX) on AMD-based systems.

Rationale:

Computers with the ability to prevent this type of code execution frequently put an option in the BIOS that will allow users to turn the feature on or off at will.

Severity: low

Identifiers: CCE-27099-1

References: CM-6(b)

#### Restrict Access to Kernel Message Buffer [ref]rule

To set the runtime status of the `kernel.dmesg_restrict` kernel parameter, run the following command:

    $ sudo sysctl -w kernel.dmesg_restrict=1

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    kernel.dmesg_restrict = 1

Rationale:

Unprivileged access to the kernel syslog can expose sensitive kernel address information.

Severity: low

Identifiers: CCE-27050-4

References: SI-11, 1314

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    #
    # Set runtime for kernel.dmesg_restrict
    #
    /sbin/sysctl -q -n -w kernel.dmesg_restrict=1

    #
    # If kernel.dmesg_restrict present in /etc/sysctl.conf, change value to "1"
    #	else, add "kernel.dmesg_restrict = 1" to /etc/sysctl.conf
    #
    if grep --silent ^kernel.dmesg_restrict /etc/sysctl.conf ; then
    	sed -i 's/^kernel.dmesg_restrict.*/kernel.dmesg_restrict = 1/g' /etc/sysctl.conf
    else
    	echo -e "\n# Set kernel.dmesg_restrict to 1 per security requirements" >> /etc/sysctl.conf
    	echo "kernel.dmesg_restrict = 1" >> /etc/sysctl.conf
    fi

### SELinux [ref]group

SELinux is a feature of the Linux kernel which can be used to guard against misconfigured or compromised programs. SELinux enforces the idea that programs should be limited in what files they can access and what actions they can take.
The default SELinux policy, as configured on Red Hat Enterprise Linux 7, has been sufficiently developed and debugged that it should be usable on almost any Red Hat machine with minimal configuration and a small amount of system administrator training. This policy prevents system services - including most of the common network-visible services such as mail servers, FTP servers, and DNS servers - from accessing files which those services have no valid reason to access. This action alone prevents a huge amount of possible damage from network attacks against services, from trojaned software, and so forth.
This guide recommends that SELinux be enabled using the default (targeted) policy on every Red Hat system, unless that system has unusual requirements which make a stronger policy appropriate.
For more information on SELinux, see https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/SELinux_Users_and_Administrators_Guide

contains 5 rules

#### Ensure SELinux Not Disabled in /etc/default/grub [ref]rule

SELinux can be disabled at boot time by an argument in `/etc/default/grub`. Remove any instances of `selinux=0` from the kernel arguments in that file to prevent SELinux from being disabled at boot.

Rationale:

Disabling a major host protection feature, such as SELinux, at boot time prevents it from confining system services at boot time. Further, it increases the chances that it will remain off during system operation.

Severity: medium

Identifiers: CCE-26961-3

References: AC-3, AC-3(3), AC-3(4), AC-4, AC-6, AU-9, SI-6(a), 22, 32, 1.4.1

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    sed -i --follow-symlinks "s/selinux=0//gI" /etc/default/grub /etc/grub2.cfg /etc/grub.d/*
    sed -i --follow-symlinks "s/enforcing=0//gI" /etc/default/grub /etc/grub2.cfg /etc/grub.d/*

#### Ensure SELinux State is Enforcing [ref]rule

The SELinux state should be set to `enforcing` at system boot time. In the file `/etc/selinux/config`, add or correct the following line to configure the system to boot into enforcing mode:

    SELINUX=enforcing

Rationale:

Setting the SELinux state to enforcing ensures SELinux is able to confine potentially compromised processes to the security policy, which is designed to prevent them from causing damage to the system or further elevating their privileges.

Severity: high

Identifiers: CCE-27334-2

References: AC-3, AC-3(3), AC-3(4), AC-4, AC-6, AU-9, SI-6(a), 2165, 2696, 1.4.2, SRG-OS-000445-GPOS-00199, RHEL-07-020210

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_selinux_state="enforcing"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/sysconfig/selinux' '^SELINUX=' $var_selinux_state 'CCE-27334-2' '%s=%s'

#### Configure SELinux Policy [ref]rule

The SELinux `targeted` policy is appropriate for general-purpose desktops and servers, as well as systems in many other roles. To configure the system to use this policy, add or correct the following line in `/etc/selinux/config`:

    SELINUXTYPE=targeted

Other policies, such as `mls`, provide additional security labeling and greater confinement but are not compatible with many general-purpose use cases. Rationale:

Setting the SELinux policy to `targeted` or a more specialized policy ensures the system will confine processes that are likely to be targeted for exploitation, such as network or system services.
Note: During the development or debugging of SELinux modules, it is common to temporarily place non-production systems in `permissive` mode. In such temporary cases, SELinux policies should be developed, and once work is completed, the system should be reconfigured to `targeted`.

Severity: high

Identifiers: CCE-27279-9

References: AC-3, AC-3(3), AC-3(4), AC-4, AC-6, AU-9, SI-6(a), 2696, 1.4.3, SRG-OS-000445-GPOS-00199, RHEL-07-020211

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_selinux_policy_name="targeted"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/sysconfig/selinux' '^SELINUXTYPE=' $var_selinux_policy_name 'CCE-27279-9' '%s=%s'

#### Ensure No Daemons are Unconfined by SELinux [ref]rule

Daemons for which the SELinux policy does not contain rules will inherit the context of the parent process. Because daemons are launched during startup and descend from the `init` process, they inherit the `initrc_t` context.
To check for unconfined daemons, run the following command:

    $ sudo ps -eZ | egrep "initrc" | egrep -vw "tr|ps|egrep|bash|awk" | tr ':' ' ' | awk '{ print $NF }'

It should produce no output in a well-configured system. Rationale:

Daemons which run with the `initrc_t` context may cause AVC denials, or allow privileges that the daemon does not require.

Severity: medium

Identifiers: CCE-27288-0

References: AC-6, AU-9, CM-7, 1.4.6

#### Ensure No Device Files are Unlabeled by SELinux [ref]rule

Device files, which are used for communication with important system resources, should be labeled with proper SELinux types. If any device files do not carry the SELinux type `device_t`, report the bug so that policy can be corrected. Supply information about what the device is and what programs use it.

Rationale:

If a device file carries the SELinux type `device_t`, then SELinux cannot properly restrict access to the device file.

Severity: medium

Identifiers: CCE-27326-8

References: AC-6, AU-9, CM-3(f), CM-7, 22, 32, 368, 318, 1812, 1813, 1814, RHEL-07-020940, SRG-OS-000480-GPOS-00227

### Account and Access Control [ref]group

In traditional Unix security, if an attacker gains shell access to a certain login account, they can perform any action or access any file to which that account has access. Therefore, making it more difficult for unauthorized people to gain shell access to accounts, particularly to privileged accounts, is a necessary part of securing a system. This section introduces mechanisms for restricting access to accounts under Red Hat Enterprise Linux 7.

contains 45 rules

### Protect Accounts by Restricting Password-Based Login [ref]group

Conventionally, Unix shell accounts are accessed by providing a username and password to a login program, which tests these values for correctness using the `/etc/passwd` and `/etc/shadow` files. Password-based login is vulnerable to guessing of weak passwords, and to sniffing and man-in-the-middle attacks against passwords entered over a network or at an insecure console. Therefore, mechanisms for accessing accounts by entering usernames and passwords should be restricted to those which are operationally necessary.

contains 11 rules

### Restrict Root Logins [ref]group

Direct root logins should be allowed only for emergency use. In normal situations, the administrator should access the system via a unique unprivileged account, and then use `su` or `sudo` to execute privileged commands. Discouraging administrators from accessing the root account directly ensures an audit trail in organizations with multiple administrators. Locking down the channels through which root can connect directly also reduces opportunities for password-guessing against the root account. The `login` program uses the file `/etc/securetty` to determine which interfaces should allow root logins. The virtual devices `/dev/console` and `/dev/tty*` represent the system consoles (accessible via the Ctrl-Alt-F1 through Ctrl-Alt-F6 keyboard sequences on a default installation). The default securetty file also contains `/dev/vc/*`. These are likely to be deprecated in most environments, but may be retained for compatibility. Root should also be prohibited from connecting via network protocols. Other sections of this document include guidance describing how to prevent root from logging in via SSH.

contains 4 rules

#### Direct root Logins Not Allowed [ref]rule

To further limit access to the `root` account, administrators can disable root logins at the console by editing the `/etc/securetty` file. This file lists all devices the root user is allowed to login to. If the file does not exist at all, the root user can login through any communication device on the system, whether via the console or via a raw network interface. This is dangerous as user can login to his machine as root via Telnet, which sends the password in plain text over the network. By default, Red Hat Enteprise Linux's `/etc/securetty` file only allows the root user to login at the console physically attached to the machine. To prevent root from logging in, remove the contents of this file. To prevent direct root logins, remove the contents of this file by typing the following command:

    $ sudo echo > /etc/securetty

Rationale:

Disabling direct root logins ensures proper accountability and multifactor authentication to privileged accounts. Users will first login, then escalate to privileged (root) access via su / sudo. This is required for FISMA Low and FISMA Moderate systems.

Severity: medium

Identifiers: CCE-27294-8

References: IA-2(1), 6.4

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    echo > /etc/securetty

#### Restrict Virtual Console Root Logins [ref]rule

To restrict root logins through the (deprecated) virtual console devices, ensure lines of this form do not appear in `/etc/securetty`:

    vc/1
    vc/2
    vc/3
    vc/4

Rationale:

Preventing direct root login to virtual console devices helps ensure accountability for actions taken on the system using the root account.

Severity: medium

Identifiers: CCE-27318-5

References: AC-6(2), 770

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    sed -i '/^vc\//d' /etc/securetty

#### Restrict Serial Port Root Logins [ref]rule

To restrict root logins on serial ports, ensure lines of this form do not appear in `/etc/securetty`:

    ttyS0
    ttyS1

Rationale:

Preventing direct root login to serial port interfaces helps ensure accountability for actions taken on the systems using the root account.

Severity: low

Identifiers: CCE-27268-2

References: AC-6(2), 770

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    sed -i '/ttyS/d' /etc/securetty

#### Verify Only Root Has UID 0 [ref]rule

If any account other than root has a UID of 0, this misconfiguration should be investigated and the accounts other than root should be removed or have their UID changed.
If the account is associated with system commands or applications the UID should be changed to one greater than "0" but less than "1000." Otherwise assign a UID greater than "1000" that has not already been assigned.

Rationale:

An account has root authority if it has a UID of 0. Multiple accounts with a UID of 0 afford more opportunity for potential intruders to guess a password for a privileged account. Proper configuration of sudo is recommended to afford multiple system administrators access to root privileges in an accountable manner.

Severity: high

Identifiers: CCE-27175-9

References: AC-6, IA-2(1), IA-4, 366, SRG-OS-000480-GPOS-00227, RHEL-07-020310

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    awk -F: '$3 == 0 && $1 != "root" { print $1 }' /etc/passwd | xargs passwd -l

### Verify Proper Storage and Existence of Password Hashes [ref]group

By default, password hashes for local accounts are stored in the second field (colon-separated) in `/etc/shadow`. This file should be readable only by processes running with root credentials, preventing users from casually accessing others' password hashes and attempting to crack them. However, it remains possible to misconfigure the system and store password hashes in world-readable files such as `/etc/passwd`, or to even store passwords themselves in plaintext on the system. Using system-provided tools for password change/creation should allow administrators to avoid such misconfiguration.

contains 3 rules

#### Prevent Log In to Accounts With Empty Password [ref]rule

If an account is configured for password authentication but does not have an assigned password, it may be possible to log into the account without authentication. Remove any instances of the `nullok` option in `/etc/pam.d/system-auth` to prevent logins with empty passwords.

Rationale:

If an account has an empty password, anyone could log in and run commands with the privileges of that account. Accounts with empty passwords should never be used in operational environments.

Severity: high

Identifiers: CCE-27286-4

References: AC-6, IA-5(b), IA-5(c), IA-5(1)(a), 366, SRG-OS-000480-GPOS-00227, RHEL-07-010260, Req-8.2.3

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    sed --follow-symlinks -i 's/\<nullok\>//g' /etc/pam.d/system-auth

#### Verify All Account Password Hashes are Shadowed [ref]rule

If any password hashes are stored in `/etc/passwd` (in the second field, instead of an `x`), the cause of this misconfiguration should be investigated. The account should have its password reset and the hash should be properly stored, or the account should be deleted entirely.

Rationale:

The hashes for all user account passwords should be stored in the file `/etc/shadow` and never in `/etc/passwd`, which is readable by all users.

Severity: medium

Identifiers: CCE-27352-4

References: IA-5(h), http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-8.2.1

#### All GIDs referenced in /etc/passwd must be defined in /etc/group [ref]rule

Add a group to the system for each GID referenced without a corresponding group.

Rationale:

If a user is assigned the Group Identifier (GID) of a group not existing on the system, and a group with the Gruop Identifier (GID) is subsequently created, the user may have unintended rights to any files associated with the group.

Severity: low

Identifiers: CCE-27503-2

References: IA-2, 764, SRG-OS-000104-GPOS-00051, RHEL-07-020300, Req-8.5.a

### Set Password Expiration Parameters [ref]group

The file `/etc/login.defs` controls several password-related settings. Programs such as `passwd`, `su`, and `login` consult `/etc/login.defs` to determine behavior with regard to password aging, expiration warnings, and length. See the man page `login.defs(5)` for more information.
Users should be forced to change their passwords, in order to decrease the utility of compromised passwords. However, the need to change passwords often should be balanced against the risk that users will reuse or write down passwords if forced to change them too often. Forcing password changes every 90-360 days, depending on the environment, is recommended. Set the appropriate value as `PASS_MAX_DAYS` and apply it to existing accounts with the `-M` flag.
The `PASS_MIN_DAYS` (`-m`) setting prevents password changes for 7 days after the first change, to discourage password cycling. If you use this setting, train users to contact an administrator for an emergency password change in case a new password becomes compromised. The `PASS_WARN_AGE` (`-W`) setting gives users 7 days of warnings at login time that their passwords are about to expire.
For example, for each existing human user USER, expiration parameters could be adjusted to a 180 day maximum password age, 7 day minimum password age, and 7 day warning period with the following command:

    $ sudo chage -M 180 -m 7 -W 7 USER

contains 2 rules

#### Set Password Minimum Age [ref]rule

To specify password minimum age for new accounts, edit the file `/etc/login.defs` and add or correct the following line, replacing DAYS appropriately:

    PASS_MIN_DAYS DAYS

A value of 1 day is considered for sufficient for many environments. The DoD requirement is 1. Rationale:

Enforcing a minimum password lifetime helps to prevent repeated password changes to defeat the password reuse or history enforcement requirement. If users are allowed to immediately and continually change their password, then the password could be repeatedly changed in a short period of time to defeat the organization's policy regarding password reuse.
Setting the minimum password age protects against users cycling back to a favorite password after satisfying the password reuse requirement.

Severity: medium

Identifiers: CCE-27002-5

References: IA-5(f), IA-5(1)(d), 198, SRG-OS-000075-GPOS-00043, RHEL-07-010200

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_accounts_minimum_age_login_defs="1"

    grep -q ^PASS_MIN_DAYS /etc/login.defs && \
      sed -i "s/PASS_MIN_DAYS.*/PASS_MIN_DAYS     $var_accounts_minimum_age_login_defs/g" /etc/login.defs
    if ! [ $? -eq 0 ]; then
        echo "PASS_MIN_DAYS      $var_accounts_minimum_age_login_defs" >> /etc/login.defs
    fi

#### Set Password Maximum Age [ref]rule

To specify password maximum age for new accounts, edit the file `/etc/login.defs` and add or correct the following line, replacing DAYS appropriately:

    PASS_MAX_DAYS DAYS

A value of 180 days is sufficient for many environments. The DoD requirement is 60. Rationale:

Any password, no matter how complex, can eventually be cracked. Therefore, passwords need to be changed periodically. If the operating system does not limit the lifetime of passwords and force users to change their passwords, there is the risk that the operating system passwords could be compromised.
Setting the password maximum age ensures users are required to periodically change their passwords. Requiring shorter password lifetimes increases the risk of users writing down the password in a convenient location subject to physical compromise.

Severity: medium

Identifiers: CCE-27051-2

References: IA-5(f), IA-5(g), IA-5(1)(d), 199, SRG-OS-000076-GPOS-00044, Req-8.2.4, 7.1.1, RHEL-07-010220

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_accounts_maximum_age_login_defs="60"

    grep -q ^PASS_MAX_DAYS /etc/login.defs && \
      sed -i "s/PASS_MAX_DAYS.*/PASS_MAX_DAYS     $var_accounts_maximum_age_login_defs/g" /etc/login.defs
    if ! [ $? -eq 0 ]; then
        echo "PASS_MAX_DAYS      $var_accounts_maximum_age_login_defs" >> /etc/login.defs
    fi

### Set Account Expiration Parameters [ref]group

Accounts can be configured to be automatically disabled after a certain time period, meaning that they will require administrator interaction to become usable again. Expiration of accounts after inactivity can be set for all accounts by default and also on a per-account basis, such as for accounts that are known to be temporary. To configure automatic expiration of an account following the expiration of its password (that is, after the password has expired and not been changed), run the following command, substituting `NUM_DAYS` and `USER` appropriately:

    $ sudo chage -I NUM_DAYS USER

Accounts, such as temporary accounts, can also be configured to expire on an explicitly-set date with the `-E` option. The file `/etc/default/useradd` controls default settings for all newly-created accounts created with the system's normal command line utilities.

contains 2 rules

#### Set Account Expiration Following Inactivity [ref]rule

To specify the number of days after a password expires (which signifies inactivity) until an account is permanently disabled, add or correct the following lines in `/etc/default/useradd`, substituting `NUM_DAYS` appropriately:

    INACTIVE=(N/A)

A value of 35 is recommended. If a password is currently on the verge of expiration, then 35 days remain until the account is automatically disabled. However, if the password will not expire for another 60 days, then 95 days could elapse until the account would be automatically disabled. See the `useradd` man page for more information. Determining the inactivity timeout must be done with careful consideration of the length of a "normal" period of inactivity for users in the particular environment. Setting the timeout too low incurs support costs and also has the potential to impact availability of the system to legitimate users. Rationale:

Disabling inactive accounts ensures that accounts which may not have been responsibly removed are not available to attackers who may have compromised their credentials.

Severity: medium

Identifiers: CCE-27355-7

References: AC-2(2), AC-2(3), IA-4(e), 795, SRG-OS-000118-GPOS-00060, RHEL-07-010280, Req-8.1.4

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_account_disable_post_pw_expiration="0"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append /etc/default/useradd INACTIVE "$var_account_disable_post_pw_expiration" '' '%s=%s'

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: "Disable POST password expiration"
      lineinfile:
        create=yes
        dest="/etc/default/useradd"
        regexp="^INACTIVE"
        line="INACTIVE=-1"

#### Assign Expiration Date to Temporary Accounts [ref]rule

Temporary accounts are established as part of normal account activation procedures when there is a need for short-term accounts. In the event temporary or emergency accounts are required, configure the system to terminate them after a documented time period. For every temporary and emergency account, run the following command to set an expiration date on it, substituting `USER` and `YYYY-MM-DD` appropriately:

    $ sudo chage -E YYYY-MM-DD USER

`YYYY-MM-DD` indicates the documented expiration date for the account. For U.S. Government systems, the operating system must be configured to automatically terminate these types of accounts after a period of 72 hours. Rationale:

If temporary user accounts remain active when no longer needed or for an excessive period, these accounts may be used to gain unauthorized access. To mitigate this risk, automated termination of all temporary accounts must be set upon account creation.

Severity: low

Identifiers: CCE-27498-5

References: AC-2(2), AC-2(3), 16, 1682, 2

### Protect Accounts by Configuring PAM [ref]group

PAM, or Pluggable Authentication Modules, is a system which implements modular authentication for Linux programs. PAM provides a flexible and configurable architecture for authentication, and it should be configured to minimize exposure to unnecessary risk. This section contains guidance on how to accomplish that.
PAM is implemented as a set of shared objects which are loaded and invoked whenever an application wishes to authenticate a user. Typically, the application must be running as root in order to take advantage of PAM, because PAM's modules often need to be able to access sensitive stores of account information, such as /etc/shadow. Traditional privileged network listeners (e.g. sshd) or SUID programs (e.g. sudo) already meet this requirement. An SUID root application, userhelper, is provided so that programs which are not SUID or privileged themselves can still take advantage of PAM.
PAM looks in the directory `/etc/pam.d` for application-specific configuration information. For instance, if the program login attempts to authenticate a user, then PAM's libraries follow the instructions in the file `/etc/pam.d/login` to determine what actions should be taken.
One very important file in `/etc/pam.d` is `/etc/pam.d/system-auth`. This file, which is included by many other PAM configuration files, defines 'default' system authentication measures. Modifying this file is a good way to make far-reaching authentication changes, for instance when implementing a centralized authentication service.

Warning: Be careful when making changes to PAM's configuration files. The syntax for these files is complex, and modifications can have unexpected consequences. The default configurations shipped with applications should be sufficient for most users.
Warning: Running `authconfig` or `system-config-authentication` will re-write the PAM configuration files, destroying any manually made changes and replacing them with a series of system defaults. One reference to the configuration file syntax can be found at http://www.kernel.org/pub/linux/libs/pam/Linux-PAM-html/sag-configuration-file.html .

contains 19 rules

### Set Password Quality Requirements [ref]group

The default `pam_pwquality` PAM module provides strength checking for passwords. It performs a number of checks, such as making sure passwords are not similar to dictionary words, are of at least a certain length, are not the previous password reversed, and are not simply a change of case from the previous password. It can also require passwords to be in certain character classes. The `pam_pwquality` module is the preferred way of configuring password requirements.
The `pam_cracklib` PAM module can also provide strength checking for passwords as the `pam_pwquality` module. It performs a number of checks, such as making sure passwords are not similar to dictionary words, are of at least a certain length, are not the previous password reversed, and are not simply a change of case from the previous password. It can also require passwords to be in certain character classes.
The man pages `pam_pwquality(8)` and `pam_cracklib(8)` provide information on the capabilities and configuration of each.

contains 10 rules

### Set Password Quality Requirements with pam_pwquality [ref]group

The `pam_pwquality` PAM module can be configured to meet requirements for a variety of policies.
For example, to configure `pam_pwquality` to require at least one uppercase character, lowercase character, digit, and other (special) character, make sure that `pam_pwquality` exists in `/etc/pam.d/system-auth`:

    password    requisite     pam_pwquality.so try_first_pass local_users_only retry=3 authtok_type=

If no such line exists, add one as the first line of the password section in `/etc/pam.d/system-auth`. Next, modify the settings in `/etc/security/pwquality.conf` to match the following:

    difok = 4
    minlen = 14
    dcredit = -1
    ucredit = -1
    lcredit = -1
    ocredit = -1
    maxrepeat = 3

The arguments can be modified to ensure compliance with your organization's security policy. Discussion of each parameter follows.
Warning: Note that the password quality requirements are not enforced for the root account for some reason.

contains 10 rules

#### Set Password Retry Prompts Permitted Per-Session [ref]rule

To configure the number of retry prompts that are permitted per-session:
Edit the `pam_pwquality.so` statement in `/etc/pam.d/system-auth` to show `retry=3`, or a lower value if site policy is more restrictive.
The DoD requirement is a maximum of 3 prompts per session.

Rationale:

Setting the password retry prompts that are permitted on a per-session basis to a low value requires some software, such as SSH, to re-connect. This can slow down and draw additional attention to some types of password-guessing attacks. Note that this is different from account lockout, which is provided by the pam_faillock module.

Severity: low

Identifiers: CCE-27160-1

References: CM-6(b), IA-5(c), 366, 6.3.2, SRG-OS-000480-GPOS-00225, RHEL-07-010410

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_password_pam_retry="3"

    if grep -q "retry=" /etc/pam.d/system-auth; then
    	sed -i --follow-symlinks "s/\(retry *= *\).*/\1$var_password_pam_retry/" /etc/pam.d/system-auth
    else
    	sed -i --follow-symlinks "/pam_pwquality.so/ s/$/ retry=$var_password_pam_retry/" /etc/pam.d/system-auth
    fi

#### Set Password Maximum Consecutive Repeating Characters [ref]rule

The pam_pwquality module's `maxrepeat` parameter controls requirements for consecutive repeating characters. When set to a positive number, it will reject passwords which contain more than that number of consecutive characters. Modify the `maxrepeat` setting in `/etc/security/pwquality.conf` to equal 2 to prevent a run of (2 + 1) or more identical characters.

Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.
Passwords with excessive repeating characters may be more vulnerable to password-guessing attacks.

Severity: medium

Identifiers: CCE-27333-4

References: IA-5, IA-5(c), 195, SRG-OS-000072-GPOS-00040, RHEL-07-010150

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_password_pam_maxrepeat="2"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/security/pwquality.conf' '^maxrepeat' $var_password_pam_maxrepeat 'CCE-27333-4' '%s = %s'

#### Set Password to Maximum of Consecutive Repeating Characters from Same Character Class [ref]rule

The pam_pwquality module's `maxclassrepeat` parameter controls requirements for consecutive repeating characters from the same character class. When set to a positive number, it will reject passwords which contain more than that number of consecutive characters from the same character class. Modify the `maxclassrepeat` setting in `/etc/security/pwquality.conf` to equal 4 to prevent a run of (4 + 1) or more identical characters.

Rationale:

Use of a complex password helps to increase the time and resources required to comrpomise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex a password, the greater the number of possible combinations that need to be tested before the password is compromised.

Severity: medium

Identifiers: CCE-27512-3

References: IA-5, IA-5(c), 195, SRG-OS-000072-GPOS-00040, RHEL-07-010160

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    var_password_pam_maxclassrepeat="4"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/security/pwquality.conf' '^maxclassrepeat' $var_password_pam_maxclassrepeat 'CCE-27512-3' '%s = %s'

#### Set Password Strength Minimum Digit Characters [ref]rule

The pam_pwquality module's `dcredit` parameter controls requirements for usage of digits in a password. When set to a negative number, any password will be required to contain that many digits. When set to a positive number, pam_pwquality will grant +1 additional length credit for each digit. Modify the `dcredit` setting in `/etc/security/pwquality.conf` to require the use of a digit in passwords.

Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possble combinations that need to be tested before the password is compromised. Requiring digits makes password guessing attacks more difficult by ensuring a larger search space.

Severity: medium

Identifiers: CCE-27214-6

References: IA-5(1)(a), IA-5(b), IA-5(c), 194, 194, SRG-OS-000071-GPOS-00039, Req-8.2.3, 6.3.2, RHEL-07-010110

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | configure

    var_password_pam_dcredit="-1"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/security/pwquality.conf' '^dcredit' $var_password_pam_dcredit 'CCE-27214-6' '%s = %s'

#### Set Password Minimum Length [ref]rule

The pam_pwquality module's `minlen` parameter controls requirements for minimum characters required in a password. Add `minlen=15` after pam_pwquality to set minimum password length requirements.

Rationale:

The shorter the password, the lower the number of possible combinations that need to be tested before the password is compromised.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. Password length is one factor of several that helps to determine strength and how long it takes to crack a password. Use of more characters in a password helps to exponentially increase the time and/or resources required to compromose the password.

Severity: medium

Identifiers: CCE-27293-0

References: IA-5(1)(a), 205, SRG-OS-000078-GPOS-00046, Req-8.2.3, 6.3.2, RHEL-07-010250

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | configure

    var_password_pam_minlen="15"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/security/pwquality.conf' '^minlen' $var_password_pam_minlen 'CCE-27293-0' '%s = %s'

#### Set Password Strength Minimum Uppercase Characters [ref]rule

The pam_pwquality module's `ucredit=` parameter controls requirements for usage of uppercase letters in a password. When set to a negative number, any password will be required to contain that many uppercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each uppercase character. Modify the `ucredit` setting in `/etc/security/pwquality.conf` to require the use of an uppercase character in passwords.

Rationale:

Use of a complex password helps to increase the time and resources reuiqred to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

Severity: medium

Identifiers: CCE-27200-5

References: IA-5(b), IA-5(c), IA-5(1)(a), 192, SRG-OS-000069-GPOS-00037, RHEL-07-010090, Req-8.2.3, 6.3.2

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_password_pam_ucredit="-1"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/security/pwquality.conf' '^ucredit' $var_password_pam_ucredit 'CCE-27200-5' '%s = %s'

#### Set Password Strength Minimum Special Characters [ref]rule

The pam_pwquality module's `ocredit=` parameter controls requirements for usage of special (or "other") characters in a password. When set to a negative number, any password will be required to contain that many special characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each special character. Modify the `ocredit` setting in `/etc/security/pwquality.conf` to equal -1 to require use of a special character in passwords.

Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possble combinations that need to be tested before the password is compromised. Requiring a minimum number of special characters makes password guessing attacks more difficult by ensuring a larger search space.

Severity: medium

Identifiers: CCE-27360-7

References: IA-5(b), IA-5(c), IA-5(1)(a), 1619, SRG-OS-000266-GPOS-00101, RHEL-07-010120

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_password_pam_ocredit="-1"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/security/pwquality.conf' '^ocredit' $var_password_pam_ocredit 'CCE-27360-7' '%s = %s'

#### Set Password Strength Minimum Lowercase Characters [ref]rule

The pam_pwquality module's `lcredit` parameter controls requirements for usage of lowercase letters in a password. When set to a negative number, any password will be required to contain that many lowercase characters. When set to a positive number, pam_pwquality will grant +1 additional length credit for each lowercase character. Modify the `lcredit` setting in `/etc/security/pwquality.conf` to require the use of a lowercase character in passwords.

Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possble combinations that need to be tested before the password is compromised. Requiring a minimum number of lowercase characters makes password guessing attacks more difficult by ensuring a larger search space.

Severity: medium

Identifiers: CCE-27345-8

References: IA-5(b), IA-5(c), IA-5(1)(a), 193, SRG-OS-000070-GPOS-00038, Req-8.2.3, RHEL-07-010100

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_password_pam_lcredit="-1"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/security/pwquality.conf' '^lcredit' $var_password_pam_lcredit 'CCE-27345-8' '%s = %s'

#### Set Password Strength Minimum Different Characters [ref]rule

The pam_pwquality module's `difok` parameter sets the number of characters in a password that must not be present in and old password during a password change. Modify the `difok` setting in `/etc/security/pwquality.conf` to equal 8 to require differing characters when changing passwords.

Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute–force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.
Requiring a minimum number of different characters during password changes ensures that newly changed passwords should not resemble previously compromised ones. Note that passwords which are changed on compromised systems will still be compromised, however.

Severity: medium

Identifiers: CCE-26631-2

References: IA-5(b), IA-5(c), IA-5(1)(b), 195, SRG-OS-000072-GPOS-00040, RHEL-07-010130

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    var_password_pam_difok="8"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/security/pwquality.conf' '^difok' $var_password_pam_difok 'CCE-26631-2' '%s = %s'

#### Set Password Strength Minimum Different Categories [ref]rule

The pam_pwquality module's `minclass` parameter controls requirements for usage of different character classes, or types, of character that must exist in a password before it is considered valid. For example, setting this value to three (3) requires that any password must have characters from at least three different categories in order to be approved. The default value is zero (0), meaning there are no required classes. There are four categories available:

    * Upper-case characters
    * Lower-case characters
    * Digits
    * Special characters (for example, punctuation)

Modify the `minclass` setting in `/etc/security/pwquality.conf` entry to require 4 differing categories of characters when changing passwords. Rationale:

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.
Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.
Requiring a minimum number of character categories makes password guessing attacks more difficult by ensuring a larger search space.

Severity: medium

Identifiers: CCE-27115-5

References: IA-5, 195, SRG-OS-000072-GPOS-00040, RHEL-07-010140

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_password_pam_minclass="4"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/security/pwquality.conf' '^minclass' $var_password_pam_minclass 'CCE-27115-5' '%s = %s'

### Set Lockouts for Failed Password Attempts [ref]group

The `pam_faillock` PAM module provides the capability to lock out user accounts after a number of failed login attempts. Its documentation is available in `/usr/share/doc/pam-VERSION/txts/README.pam_faillock`.

Warning: Locking out user accounts presents the risk of a denial-of-service attack. The lockout policy must weigh whether the risk of such a denial-of-service attack outweighs the benefits of thwarting password guessing attacks.

contains 5 rules

#### Set Deny For Failed Password Attempts [ref]rule

To configure the system to lock out accounts after a number of incorrect login attempts using `pam_faillock.so`, modify the content of both `/etc/pam.d/system-auth` and `/etc/pam.d/password-auth` as follows:

- add the following line immediately `before` the `pam_unix.so` statement in the `AUTH` section:

      auth required pam_faillock.so preauth silent deny=3 unlock_time=604800 fail_interval=900

- add the following line immediately `after` the `pam_unix.so` statement in the `AUTH` section:

      auth [default=die] pam_faillock.so authfail deny=3 unlock_time=604800 fail_interval=900

- add the following line immediately `before` the `pam_unix.so` statement in the `ACCOUNT` section:

      account required pam_faillock.so

Rationale:

Locking out user accounts after a number of incorrect attempts prevents direct password guessing attacks.

Severity: medium

Identifiers: CCE-27350-8

References: AC-7(b), 2238, SRG-OS-000329-GPOS-00128, SRG-OS-000021-GPOS-00005, RHEL-07-010371, Req-8.1.6, 6.3.3

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_accounts_passwords_pam_faillock_deny="3"

    AUTH_FILES[0]="/etc/pam.d/system-auth"
    AUTH_FILES[1]="/etc/pam.d/password-auth"

    for pamFile in "${AUTH_FILES[@]}"
    do

    	# pam_faillock.so already present?
    	if grep -q "^auth.*pam_faillock.so.*" $pamFile; then

    		# pam_faillock.so present, deny directive present?
    		if grep -q "^auth.*[default=die].*pam_faillock.so.*authfail.*deny=" $pamFile; then

    			# both pam_faillock.so & deny present, just correct deny directive value
    			sed -i --follow-symlinks "s/\(^auth.*required.*pam_faillock.so.*preauth.*silent.*\)\(deny *= *\).*/\1\2$var_accounts_passwords_pam_faillock_deny/" $pamFile
    			sed -i --follow-symlinks "s/\(^auth.*[default=die].*pam_faillock.so.*authfail.*\)\(deny *= *\).*/\1\2$var_accounts_passwords_pam_faillock_deny/" $pamFile

    		# pam_faillock.so present, but deny directive not yet
    		else

    			# append correct deny value to appropriate places
    			sed -i --follow-symlinks "/^auth.*required.*pam_faillock.so.*preauth.*silent.*/ s/$/ deny=$var_accounts_passwords_pam_faillock_deny/" $pamFile
    			sed -i --follow-symlinks "/^auth.*[default=die].*pam_faillock.so.*authfail.*/ s/$/ deny=$var_accounts_passwords_pam_faillock_deny/" $pamFile
    		fi

    	# pam_faillock.so not present yet
    	else

    		# insert pam_faillock.so preauth & authfail rows with proper value of the 'deny' option
    		sed -i --follow-symlinks "/^auth.*sufficient.*pam_unix.so.*/i auth        required      pam_faillock.so preauth silent deny=$var_accounts_passwords_pam_faillock_deny" $pamFile
    		sed -i --follow-symlinks "/^auth.*sufficient.*pam_unix.so.*/a auth        [default=die] pam_faillock.so authfail deny=$var_accounts_passwords_pam_faillock_deny" $pamFile
    		sed -i --follow-symlinks "/^account.*required.*pam_unix.so/i account     required      pam_faillock.so" $pamFile
    	fi
    done

#### Set Lockout Time For Failed Password Attempts [ref]rule

To configure the system to lock out accounts after a number of incorrect login attempts and require an administrator to unlock the account using `pam_faillock.so`, modify the content of both `/etc/pam.d/system-auth` and `/etc/pam.d/password-auth` as follows:

- add the following line immediately `before` the `pam_unix.so` statement in the `AUTH` section:

      auth required pam_faillock.so preauth silent deny=3 unlock_time=604800 fail_interval=900

- add the following line immediately `after` the `pam_unix.so` statement in the `AUTH` section:

      auth [default=die] pam_faillock.so authfail deny=3 unlock_time=604800 fail_interval=900

- add the following line immediately `before` the `pam_unix.so` statement in the `ACCOUNT` section:

      account required pam_faillock.so

Rationale:

Locking out user accounts after a number of incorrect attempts prevents direct password guessing attacks. Ensuring that an administrator is involved in unlocking locked accounts draws appropriate attention to such situations.

Severity: medium

Identifiers: CCE-26884-7

References: AC-7(b), 002238, SRG-OS-000329-GPOS-00128, SRG-OS-000021-GPOS-00005, RHEL-07-010372, Req-8.1.7, 6.3.3

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_accounts_passwords_pam_faillock_unlock_time="604800"

    AUTH_FILES[0]="/etc/pam.d/system-auth"
    AUTH_FILES[1]="/etc/pam.d/password-auth"

    for pamFile in "${AUTH_FILES[@]}"
    do

    	# pam_faillock.so already present?
    	if grep -q "^auth.*pam_faillock.so.*" $pamFile; then

    		# pam_faillock.so present, unlock_time directive present?
    		if grep -q "^auth.*[default=die].*pam_faillock.so.*authfail.*unlock_time=" $pamFile; then

    			# both pam_faillock.so & unlock_time present, just correct unlock_time directive value
    			sed -i --follow-symlinks "s/\(^auth.*required.*pam_faillock.so.*preauth.*silent.*\)\(unlock_time *= *\).*/\1\2$var_accounts_passwords_pam_faillock_unlock_time/" $pamFile
    			sed -i --follow-symlinks "s/\(^auth.*[default=die].*pam_faillock.so.*authfail.*\)\(unlock_time *= *\).*/\1\2$var_accounts_passwords_pam_faillock_unlock_time/" $pamFile

    		# pam_faillock.so present, but unlock_time directive not yet
    		else

    			# append correct unlock_time value to appropriate places
    			sed -i --follow-symlinks "/^auth.*required.*pam_faillock.so.*preauth.*silent.*/ s/$/ unlock_time=$var_accounts_passwords_pam_faillock_unlock_time/" $pamFile
    			sed -i --follow-symlinks "/^auth.*[default=die].*pam_faillock.so.*authfail.*/ s/$/ unlock_time=$var_accounts_passwords_pam_faillock_unlock_time/" $pamFile
    		fi

    	# pam_faillock.so not present yet
    	else

    		# insert pam_faillock.so preauth & authfail rows with proper value of the 'unlock_time' option
    		sed -i --follow-symlinks "/^auth.*sufficient.*pam_unix.so.*/i auth        required      pam_faillock.so preauth silent unlock_time=$var_accounts_passwords_pam_faillock_unlock_time" $pamFile
    		sed -i --follow-symlinks "/^auth.*sufficient.*pam_unix.so.*/a auth        [default=die] pam_faillock.so authfail unlock_time=$var_accounts_passwords_pam_faillock_unlock_time" $pamFile
    		sed -i --follow-symlinks "/^account.*required.*pam_unix.so/i account     required      pam_faillock.so" $pamFile
    	fi
    done

#### Configure the root Account for Failed Password Attempts [ref]rule

To configure the system to lock out the `root` account after a number of incorrect login attempts using `pam_faillock.so`, modify the content of both `/etc/pam.d/system-auth` and `/etc/pam.d/password-auth` as follows:

- Modify the following line in the `AUTH` section to add `even_deny_root`:

      auth required pam_faillock.so preauth silent even_deny_root deny=3 unlock_time=604800 fail_interval=900

- Modify the following line in the `AUTH` section to add `even_deny_root`:

      auth [default=die] pam_faillock.so authfail even_deny_root deny=3 unlock_time=604800 fail_interval=900

Rationale:

By limiting the number of failed logon attempts, the risk of unauthorized system access via user password guessing, otherwise known as brute-forcing, is reduced. Limits are imposed by locking the account.

Severity: medium

Identifiers: CCE-80353-6

References: AC-7(b), 2238, SRG-OS-000329-GPOS-00128, SRG-OS-000021-GPOS-00005, RHEL-07-010373

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    if [ $( grep -c "auth.*required.*pam_faillock.so.*even_deny_root" /etc/pam.d/system-auth ) -eq 0 ]; then
            BEGINNING_TXT=$( cat /etc/pam.d/system-auth | grep "auth.*required.*pam_faillock.so" | sed -e 's/[]\/$*.^|[]/\\&/g' )
    	sed -i --follow-symlinks "s/$BEGINNING_TXT/$BEGINNING_TXT even_deny_root/" /etc/pam.d/system-auth
    fi

    if [ $( grep -c "auth.*default.*die.*pam_faillock.so.*even_deny_root" /etc/pam.d/system-auth ) -eq 0 ]; then
            BEGINNING_TXT=$( cat /etc/pam.d/system-auth | grep "auth.*default.*die.*pam_faillock.so"  | sed -e 's/[]\/$*.^|[]/\\&/g' )
    	sed -i --follow-symlinks "s/$BEGINNING_TXT/$BEGINNING_TXT even_deny_root/" /etc/pam.d/system-auth
    fi

#### Set Interval For Counting Failed Password Attempts [ref]rule

Utilizing `pam_faillock.so`, the `fail_interval` directive configures the system to lock out an accounts after a number of incorrect login attempts within a specified time period.. Modify the content of both `/etc/pam.d/system-auth` and `/etc/pam.d/password-auth` as follows:

- Add the following line immediately `before` the `pam_unix.so` statement in the `AUTH` section:

      auth required pam_faillock.so preauth silent deny=3 unlock_time=604800 fail_interval=900

- Add the following line immediately `after` the `pam_unix.so` statement in the `AUTH` section:

      auth [default=die] pam_faillock.so authfail deny=3 unlock_time=604800 fail_interval=900

- Add the following line immediately `before` the `pam_unix.so` statement in the `ACCOUNT` section:

      account required pam_faillock.so

Rationale:

By limiting the number of failed logon attempts the risk of unauthorized system access via user password guessing, otherwise known as brute-forcing, is reduced. Limits are imposed by locking the account.

Severity: medium

Identifiers: CCE-27297-1

References: AC-7(b), 2238, SRG-OS-000329-GPOS-00128, SRG-OS-000021-GPOS-00005, RHEL-07-010371

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_accounts_passwords_pam_faillock_fail_interval="900"

    AUTH_FILES[0]="/etc/pam.d/system-auth"
    AUTH_FILES[1]="/etc/pam.d/password-auth"

    for pamFile in "${AUTH_FILES[@]}"
    do

    	# pam_faillock.so already present?
    	if grep -q "^auth.*pam_faillock.so.*" $pamFile; then

    		# pam_faillock.so present, 'fail_interval' directive present?
    		if grep -q "^auth.*[default=die].*pam_faillock.so.*authfail.*fail_interval=" $pamFile; then

    			# both pam_faillock.so & 'fail_interval' present, just correct 'fail_interval' directive value
    			sed -i --follow-symlinks "s/\(^auth.*required.*pam_faillock.so.*preauth.*silent.*\)\(fail_interval *= *\).*/\1\2$var_accounts_passwords_pam_faillock_fail_interval/" $pamFile
    			sed -i --follow-symlinks "s/\(^auth.*[default=die].*pam_faillock.so.*authfail.*\)\(fail_interval *= *\).*/\1\2$var_accounts_passwords_pam_faillock_fail_interval/" $pamFile

    		# pam_faillock.so present, but 'fail_interval' directive not yet
    		else

    			# append correct 'fail_interval' value to appropriate places
    			sed -i --follow-symlinks "/^auth.*required.*pam_faillock.so.*preauth.*silent.*/ s/$/ fail_interval=$var_accounts_passwords_pam_faillock_fail_interval/" $pamFile
    			sed -i --follow-symlinks "/^auth.*[default=die].*pam_faillock.so.*authfail.*/ s/$/ fail_interval=$var_accounts_passwords_pam_faillock_fail_interval/" $pamFile
    		fi

    	# pam_faillock.so not present yet
    	else

    		# insert pam_faillock.so preauth & authfail rows with proper value of the 'fail_interval' option
    		sed -i --follow-symlinks "/^auth.*sufficient.*pam_unix.so.*/i auth        required      pam_faillock.so preauth silent fail_interval=$var_accounts_passwords_pam_faillock_fail_interval" $pamFile
    		sed -i --follow-symlinks "/^auth.*sufficient.*pam_unix.so.*/a auth        [default=die] pam_faillock.so authfail fail_interval=$var_accounts_passwords_pam_faillock_fail_interval" $pamFile
    		sed -i --follow-symlinks "/^account.*required.*pam_unix.so/i account     required      pam_faillock.so" $pamFile
    	fi
    done

#### Limit Password Reuse [ref]rule

Do not allow users to reuse recent passwords. This can be accomplished by using the `remember` option for the `pam_unix` or `pam_pwhistory` PAM modules.
In the file `/etc/pam.d/system-auth`, append `remember=5` to the line which refers to the `pam_unix.so` or `pam_pwhistory.so`module, as shown below:

- for the `pam_unix.so` case:

      password sufficient pam_unix.so ...existing_options... remember=5

- for the `pam_pwhistory.so` case:

      password requisite pam_pwhistory.so ...existing_options... remember=5

The DoD STIG requirement is 5 passwords.Rationale:

Preventing re-use of previous passwords helps ensure that a compromised password is not re-used by a user.

Severity: medium

Identifiers: CCE-26923-3

References: IA-5(f), IA-5(1)(e), 200, SRG-OS-000077-GPOS-00045, RHEL-07-010240, Req-8.2.5, 6.3.4

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_password_pam_unix_remember="5"

    if grep -q "remember=" /etc/pam.d/system-auth; then
    	sed -i --follow-symlinks "s/\(^password.*sufficient.*pam_unix.so.*\)\(\(remember *= *\)[^ $]*\)/\1remember=$var_password_pam_unix_remember/" /etc/pam.d/system-auth
    else
    	sed -i --follow-symlinks "/^password[[:space:]]\+sufficient[[:space:]]\+pam_unix.so/ s/$/ remember=$var_password_pam_unix_remember/" /etc/pam.d/system-auth
    fi

### Set Password Hashing Algorithm [ref]group

The system's default algorithm for storing password hashes in `/etc/shadow` is SHA-512. This can be configured in several locations.

contains 3 rules

#### Set PAM's Password Hashing Algorithm [ref]rule

The PAM system service can be configured to only store encrypted representations of passwords. In `/etc/pam.d/system-auth`, the `password` section of the file controls which PAM modules execute during a password change. Set the `pam_unix.so` module in the `password` section to include the argument `sha512`, as shown below:

    password    sufficient    pam_unix.so sha512 other arguments...

This will help ensure when local users change their passwords, hashes for the new passwords will be generated using the SHA-512 algorithm. This is the default. Rationale:

Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kepy in plain text.
This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the `crypt_style` configuration option ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult.

Severity: medium

Identifiers: CCE-27104-9

References: IA-5(b), IA-5(c), IA-5(1)(c), IA-7, 196, SRG-OS-000073-GPOS-00041, RHEL-07-010170, Req-8.2.1, 6.3.1

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    if ! grep -q "^password.*sufficient.*pam_unix.so.*sha512" /etc/pam.d/system-auth; then
    	sed -i --follow-symlinks "/^password.*sufficient.*pam_unix.so/ s/$/ sha512/" /etc/pam.d/system-auth
    fi

#### Set Password Hashing Algorithm in /etc/login.defs [ref]rule

In `/etc/login.defs`, add or correct the following line to ensure the system will use SHA-512 as the hashing algorithm:

    ENCRYPT_METHOD SHA512

Rationale:

Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kept in plain text.
Using a stronger hashing algorithm makes password cracking attacks more difficult.

Severity: medium

Identifiers: CCE-27124-7

References: IA-5(b), IA-5(c), IA-5(1)(c), IA-7, 196, SRG-OS-000073-GPOS-00041, RHEL-07-010180, Req-8.2.1, 6.3.1

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    if grep --silent ^ENCRYPT_METHOD /etc/login.defs ; then
    	sed -i 's/^ENCRYPT_METHOD.*/ENCRYPT_METHOD SHA512/g' /etc/login.defs
    else
    	echo "" >> /etc/login.defs
    	echo "ENCRYPT_METHOD SHA512" >> /etc/login.defs
    fi

#### Set Password Hashing Algorithm in /etc/libuser.conf [ref]rule

In `/etc/libuser.conf`, add or correct the following line in its `[defaults]` section to ensure the system will use the SHA-512 algorithm for password hashing:

    crypt_style = sha512

Rationale:

Passwords need to be protected at all times, and encryption is the standard method for protecting passwords. If passwords are not encrypted, they can be plainly read (i.e., clear text) and easily compromised. Passwords that are encrypted with a weak algorithm are no more protected than if they are kepy in plain text.
This setting ensures user and group account administration utilities are configured to store only encrypted representations of passwords. Additionally, the `crypt_style` configuration option ensures the use of a strong hashing algorithm that makes password cracking attacks more difficult.

Severity: medium

Identifiers: CCE-27053-8

References: IA-5(b), IA-5(c), IA-5(1)(c), IA-7, 196, SRG-OS-000073-GPOS-00041, RHEL-07-010190, Req-8.2.1

#### Set Last Logon/Access Notification [ref]rule

To configure the system to notify users of last logon/access using `pam_lastlog`, add or correct the `pam_lastlog` settings in `/etc/pam.d/postlogin` to read as follows:

    session     [success=1 default=ignore] pam_succeed_if.so service !~ gdm* service !~ su* quiet
    session     [default=1]   pam_lastlog.so nowtmp showfailed
    session     optional      pam_lastlog.so silent noupdate showfailed

Rationale:

Users need to be aware of activity that occurs regarding their account. Providing users with information regarding the number of unsuccessful attempts that were made to login to their account allows the user to determine if any unauthorized activity has occurred and gives them an opportunity to notify administrators.

Severity: low

Identifiers: CCE-27275-7

References: AC-9, 366, Req-10.2.4, SRG-OS-000480-GPOS-00227, RHEL-07-040300

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    if ! `grep -q ^[^#].*pam_succeed_if.*showfailed /etc/pam.d/postlogin` ; then
      if ! grep `^session.*pam_succeed_if.so /etc/pam.d/postlogin` ; then
        echo "session     [default=1]   pam_lastlog.so nowtmp showfailed" >> /etc/pam.d/postlogin
        echo "session     optional      pam_lastlog.so silent noupdate showfailed" >> /etc/pam.d/postlogin
      else
        sed -i '/^session.*pam_succeed_if.so/a session\t    optional\t  pam_lastlog.so silent noupdate showfailed' /etc/pam.d/postlogin
        sed -i '/^session.*pam_succeed_if.so/a session\t    [default=1]\t  pam_lastlog.so nowtmp showfailed' /etc/pam.d/postlogin
      fi
    else
      sed -i "s/session[ ]*\[default=1][ ]*pam_lastlog.so.*/session     [default=1]   pam_lastlog.so nowtmp showfailed/g" /etc/pam.d/postlogin
      sed -i "s/session[ ]*optional[ ]*pam_lastlog.so.*/session     optional      pam_lastlog.so silent noupdate showfailed/g" /etc/pam.d/postlogin
    fi

### Secure Session Configuration Files for Login Accounts [ref]group

When a user logs into a Unix account, the system configures the user's session by reading a number of files. Many of these files are located in the user's home directory, and may have weak permissions as a result of user error or misconfiguration. If an attacker can modify or even read certain types of account configuration information, they can often gain full access to the affected user's account. Therefore, it is important to test and correct configuration file permissions for interactive accounts, particularly those of privileged users such as root or system administrators.

contains 4 rules

### Ensure that Users Have Sensible Umask Values [ref]group

The umask setting controls the default permissions for the creation of new files. With a default `umask` setting of 077, files and directories created by users will not be readable by any other user on the system. Users who wish to make specific files group- or world-readable can accomplish this by using the chmod command. Additionally, users can make all their files readable to their group by default by setting a `umask` of 027 in their shell configuration files. If default per-user groups exist (that is, if every user has a default group whose name is the same as that user's username and whose only member is the user), then it may even be safe for users to select a `umask` of 007, making it very easy to intentionally share files with groups of which the user is a member.

contains 1 rule

#### Ensure the Default Umask is Set Correctly in login.defs [ref]rule

To ensure the default umask controlled by `/etc/login.defs` is set properly, add or correct the `UMASK` setting in `/etc/login.defs` to read as follows:

    UMASK 077

Rationale:

The umask value influences the permissions assigned to files when they are created. A misconfigured umask value could result in files with excessive permissions that can be read and written to by unauthorized users.

Severity: low

Identifiers: CCE-80205-8

References: CM-6(b), SA-8, 366, SRG-OS-000480-GPOS-00228, RHEL-07-020230

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_accounts_user_umask="077"

    grep -q UMASK /etc/login.defs && \
      sed -i "s/UMASK.*/UMASK $var_accounts_user_umask/g" /etc/login.defs
    if ! [ $? -eq 0 ]; then
        echo "UMASK $var_accounts_user_umask" >> /etc/login.defs
    fi

#### Set Interactive Session Timeout [ref]rule

Setting the `TMOUT` option in `/etc/profile` ensures that RHEL7 will terminate all user sessions based on inactivity.

Rationale:

Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been left unattended.

Severity: medium

Identifiers: CCE-27557-8

References: AC-12, SC-10, 1133, 0361, SRG-OS-000163-GPOS-00072, RHEL-07-040160

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_accounts_tmout="600"

    if grep --silent ^TMOUT /etc/profile ; then
            sed -i "s/^TMOUT.*/TMOUT = $var_accounts_tmout/g" /etc/profile
    else
            echo -e "\n# Set TMOUT to $var_accounts_tmout per security requirements" >> /etc/profile
            echo "TMOUT = $var_accounts_tmout" >> /etc/profile
    fi

#### Limit the Number of Concurrent Login Sessions Allowed Per User [ref]rule

Limiting the number of allowed users and sessions per user can limit risks related to Denial of Service attacks. This addresses concurrent sessions for a single account and does not address concurrent sessions by a single user via multiple accounts. To set the number of concurrent sessions per user add the following line in `/etc/security/limits.conf`:

    * hard maxlogins 10

Rationale:

Limiting simultaneous user logins can insulate the system from denial of service problems caused by excessive logins. Automated login processes operating improperly or maliciously may result in an exceptional number of simultaneous login sessions.

Severity: low

Identifiers: CCE-27081-9

References: AC-10, 54, SRG-OS-000027-GPOS-00008, RHEL-07-040010

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_accounts_max_concurrent_login_sessions="10"

    if grep -q '^[^#]*\<maxlogins\>' /etc/security/limits.d/*.conf; then
    	sed -i "/^[^#]*\<maxlogins\>/ s/maxlogins.*/maxlogins $var_accounts_max_concurrent_login_sessions/" /etc/security/limits.d/*.conf
    elif grep -q '^[^#]*\<maxlogins\>' /etc/security/limits.conf; then
    	sed -i "/^[^#]*\<maxlogins\>/ s/maxlogins.*/maxlogins $var_accounts_max_concurrent_login_sessions/" /etc/security/limits.conf
    else
    	echo "*	hard	maxlogins	$var_accounts_max_concurrent_login_sessions" >> /etc/security/limits.conf
    fi

#### Ensure the Logon Failure Delay is Set Correctly in login.defs [ref]rule

To ensure the logon failure delay controlled by `/etc/login.defs` is set properly, add or correct the `FAIL_DELAY` setting in `/etc/login.defs` to read as follows:

    FAIL_DELAY 4

Rationale:

Increasing the time between a failed authentication attempt and re-prompting to enter credentials helps to slow a single-threaded brute force attack.

Severity: low

Identifiers: CCE-80352-8

References: CM-6(b), 366, SRG-OS-000480-GPOS-00226, RHEL-07-010420

### Protect Physical Console Access [ref]group

It is impossible to fully protect a system from an attacker with physical access, so securing the space in which the system is located should be considered a necessary step. However, there are some steps which, if taken, make it more difficult for an attacker to quickly or undetectably modify a system from its console.

contains 8 rules

### Set Boot Loader Password [ref]group

During the boot process, the boot loader is responsible for starting the execution of the kernel and passing options to it. The boot loader allows for the selection of different kernels - possibly on different partitions or media. The default Red Hat Enterprise Linux boot loader for x86 systems is called GRUB2. Options it can pass to the kernel include single-user mode, which provides root access without any authentication, and the ability to disable SELinux. To prevent local users from modifying the boot parameters and endangering security, protect the boot loader configuration with a password and ensure its configuration file's permissions are set properly.

contains 2 rules

#### Set Boot Loader Password [ref]rule

The grub2 boot loader should have a superuser account and password protection enabled to protect boot-time settings.
To do so, select a superuser account and password and add them into the `/etc/grub.d/01_users` configuration file.
Since plaintext passwords are a security risk, generate a hash for the pasword by running the following command:

    $ grub2-mkpasswd-pbkdf2

When prompted, enter the password that was selected and insert the returned password hash into the `/etc/grub.d/01_users` configuration file immediately after the superuser account. (Use the output from `grub2-mkpasswd-pbkdf2` as the value of password-hash):

    password_pbkdf2 superusers-account password-hash

NOTE: It is recommended not to use common administrator account names like root, admin, or administrator for the grub2 superuser account.
To meet FISMA Moderate, the bootloader superuser account and password MUST differ from the root account and password. Once the superuser account and password have been added, update the `grub.cfg` file by running:

    grub2-mkconfig -o /boot/grub2/grub.cfg

NOTE: Do NOT manually add the superuser account and password to the `grub.cfg` file as the grub2-mkconfig command overwrites this file. Rationale:

Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode. For more information on how to configure the grub2 superuser account and password, please refer to

- https://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/sec-GRUB_2_Password_Protection.html
.

Severity: high

Identifiers: CCE-27309-4

References: IA-2(1), IA-5(e), AC-3, 213, SRG-OS-000080-GPOS-00048, RHEL-07-010460, 1.5.3

#### Set the UEFI Boot Loader Password [ref]rule

The UEFI grub2 boot loader should have a superuser account and password protection enabled to protect boot-time settings.
To do so, select a superuser account and password and add them into the `/etc/grub.d/01_users` configuration file.
Since plaintext passwords are a security risk, generate a hash for the pasword by running the following command:

    $ grub2-mkpasswd-pbkdf2

When prompted, enter the password that was selected and insert the returned password hash into the `/etc/grub.d/01_users` configuration file immediately after the superuser account. (Use the output from `grub2-mkpasswd-pbkdf2` as the value of password-hash):

    password_pbkdf2 superusers-account password-hash

NOTE: It is recommended not to use common administrator account names like root, admin, or administrator for the grub2 superuser account.
To meet FISMA Moderate, the bootloader superuser account and password MUST differ from the root account and password. Once the superuser account and password have been added, update the `grub.cfg` file by running:

    grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

NOTE: Do NOT manually add the superuser account and password to the `grub.cfg` file as the grub2-mkconfig command overwrites this file. Rationale:

Password protection on the boot loader configuration ensures users with physical access cannot trivially alter important bootloader settings. These include which kernel to use, and whether to enter single-user mode. For more information on how to configure the grub2 superuser account and password, please refer to

- https://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/sec-GRUB_2_Password_Protection.html
.

Severity: medium

Identifiers: CCE-80354-4

References: AC-3, 213, SRG-OS-000080-GPOS-00048, RHEL-07-010470

### Configure Screen Locking [ref]group

When a user must temporarily leave an account logged-in, screen locking should be employed to prevent passersby from abusing the account. User education and training is particularly important for screen locking to be effective, and policies can be implemented to reinforce this.
Automatic screen locking is only meant as a safeguard for those cases where a user forgot to lock the screen.

contains 2 rules

### Configure Console Screen Locking [ref]group

A console screen locking mechanism is provided in the `screen` package, which is not installed by default.

contains 1 rule

#### Install the screen Package [ref]rule

To enable console screen locking, install the `screen` package:

    $ sudo yum install screen

Instruct users to begin new terminal sessions with the following command:

    $ screen

The console can now be locked with the following key combination:

    ctrl+a x

Rationale:

A session time-out lock is a temporary action taken when a user stops work and moves away from the immediate physical vicinity of the information system but des not logout because of the temporary nature of the absence. Rather than relying on the user to manually lock their operation system session prior to vacating the vicinity, operating systems need to be able to identify when a user's session has idled and take action to initiate the session lock.
The `screen` package allows for a session lock to be implemented and configured.

Severity: medium

Identifiers: CCE-27351-6

References: AC-11(a), 57, SRG-OS-000029-GPOS-00010, RHEL-07-010072

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command install screen

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    - name: Ensure screen is installed
      package:
        name="{{item}}"
        state=present
      with_items:
        - screen

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    include install_screen

    class install_screen {
      package { 'screen':
        ensure => 'installed',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    package --add=screen

### Hardware Tokens for Authentication [ref]group

The use of hardware tokens such as smart cards for system login provides stronger, two-factor authentication than using a username and password. In Red Hat Enterprise Linux servers and workstations, hardware token login is not enabled by default and must be enabled in the system settings.

contains 1 rule

#### Enable Smart Card Login [ref]rule

To enable smart card authentication, consult the documentation at:

- https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/System-Level_Authentication_Guide/smartcards.html#authconfig-smartcards

For guidance on enabling SSH to authenticate against a Common Access Card (CAC), consult documentation at:

- https://access.redhat.com/solutions/82273

Rationale:

Smart card login provides two-factor authentication stronger than that provided by a username and password combination. Smart cards leverage PKI (public key infrastructure) in order to provide and verify credentials.

Severity: medium

Identifiers: CCE-80207-4

References: IA-2(2), 765, 766, 767, 768, 771, 772, 884, Req-8.3, RHEL-07-010500, SRG-OS-000104-GPOS-00051, SRG-OS-000106-GPOS-00053, SRG-OS-000107-GPOS-00054, SRG-OS-000109-GPOS-00056, SRG-OS-000108-GPOS-00055, SRG-OS-000108-GPOS-00057, SRG-OS-000108-GPOS-00058

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Install required packages

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command install esc
    package_command install pam_pkcs11

    # Enable pcscd.socket systemd activation socket

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

    service_command enable pcscd.socket

    # Configure the expected /etc/pam.d/system-auth{,-ac} settings directly
    #
    # The code below will configure system authentication in the way smart card
    # logins will be enabled, but also user login(s) via other method to be allowed
    #
    # NOTE: It is not possible to use the 'authconfig' command to perform the
    #       remediation for us, because call of 'authconfig' would discard changes
    #       for other remediations (see RH BZ#1357019 for details)
    #
    #	Therefore we need to configure the necessary settings directly.
    #

    # Define system-auth config location
    SYSTEM_AUTH_CONF="/etc/pam.d/system-auth"
    # Define expected 'pam_env.so' row in $SYSTEM_AUTH_CONF
    PAM_ENV_SO="auth.*required.*pam_env.so"

    # Define 'pam_succeed_if.so' row to be appended past $PAM_ENV_SO row into $SYSTEM_AUTH_CONF
    SYSTEM_AUTH_PAM_SUCCEED="\
    auth        \[success=1 default=ignore\] pam_succeed_if.so service notin \
    login:gdm:xdm:kdm:xscreensaver:gnome-screensaver:kscreensaver quiet use_uid"
    # Define 'pam_pkcs11.so' row to be appended past $SYSTEM_AUTH_PAM_SUCCEED
    # row into SYSTEM_AUTH_CONF file
    SYSTEM_AUTH_PAM_PKCS11="\
    auth        \[success=done authinfo_unavail=ignore ignore=ignore default=die\] \
    pam_pkcs11.so nodebug"

    # Define smartcard-auth config location
    SMARTCARD_AUTH_CONF="/etc/pam.d/smartcard-auth"
    # Define 'pam_pkcs11.so' auth section to be appended past $PAM_ENV_SO into $SMARTCARD_AUTH_CONF
    SMARTCARD_AUTH_SECTION="\
    auth        [success=done ignore=ignore default=die] pam_pkcs11.so wait_for_card card_only"
    # Define expected 'pam_permit.so' row in $SMARTCARD_AUTH_CONF
    PAM_PERMIT_SO="account.*required.*pam_permit.so"
    # Define 'pam_pkcs11.so' password section
    SMARTCARD_PASSWORD_SECTION="\
    password    required      pam_pkcs11.so"

    # First Correct the SYSTEM_AUTH_CONF configuration
    if ! grep -q 'pam_pkcs11.so' "$SYSTEM_AUTH_CONF"
    then
    	# Append (expected) pam_succeed_if.so row past the pam_env.so into SYSTEM_AUTH_CONF file
    	sed -i --follow-symlinks -e '/^'"$PAM_ENV_SO"'/a '"$SYSTEM_AUTH_PAM_SUCCEED" "$SYSTEM_AUTH_CONF"
    	# Append (expected) pam_pkcs11.so row past the pam_succeed_if.so into SYSTEM_AUTH_CONF file
    	sed -i --follow-symlinks -e '/^'"$SYSTEM_AUTH_PAM_SUCCEED"'/a '"$SYSTEM_AUTH_PAM_PKCS11" "$SYSTEM_AUTH_CONF"
    fi

    # Then also correct the SMARTCARD_AUTH_CONF
    if ! grep -q 'pam_pkcs11.so' "$SMARTCARD_AUTH_CONF"
    then
    	# Append (expected) SMARTCARD_AUTH_SECTION row past the pam_env.so into SMARTCARD_AUTH_CONF file
    	sed -i --follow-symlinks -e '/^'"$PAM_ENV_SO"'/a '"$SMARTCARD_AUTH_SECTION" "$SMARTCARD_AUTH_CONF"
    	# Append (expected) SMARTCARD_PASSWORD_SECTION row past the pam_permit.so into SMARTCARD_AUTH_CONF file
    	sed -i --follow-symlinks -e '/^'"$PAM_PERMIT_SO"'/a '"$SMARTCARD_PASSWORD_SECTION" "$SMARTCARD_AUTH_CONF"
    fi

    # Perform /etc/pam_pkcs11/pam_pkcs11.conf settings below
    # Define selected constants for later reuse
    SP="[:space:]"
    PAM_PKCS11_CONF="/etc/pam_pkcs11/pam_pkcs11.conf"

    # Ensure OCSP is turned on in $PAM_PKCS11_CONF
    # 1) First replace any occurrence of 'none' value of 'cert_policy' key setting with the correct configuration
    sed -i "s/^[$SP]*cert_policy[$SP]\+=[$SP]\+none;/\t\tcert_policy = ca, ocsp_on, signature;/g" "$PAM_PKCS11_CONF"
    # 2) Then append 'ocsp_on' value setting to each 'cert_policy' key in $PAM_PKCS11_CONF configuration line,
    # which does not contain it yet
    sed -i "/ocsp_on/! s/^[$SP]*cert_policy[$SP]\+=[$SP]\+\(.*\);/\t\tcert_policy = \1, ocsp_on;/" "$PAM_PKCS11_CONF"

#### Require Authentication for Single User Mode [ref]rule

Single-user mode is intended as a system recovery method, providing a single user root access to the system by providing a boot option at startup. By default, no authentication is performed if single-user mode is selected.
By default, single-user mode is protected by requiring a password and is set in `/usr/lib/systemd/system/rescue.service`.

Rationale:

This prevents attackers with physical access from trivially bypassing security on the machine and gaining root access. Such accesses are further prevented by configuring the bootloader password.

Severity: medium

Identifiers: CCE-27287-2

References: IA-2(1), AC-3, 213

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    grep -q sulogin /usr/lib/systemd/system/rescue.service
    if ! [ $? -eq 0 ]; then
        sed -i "s/-c \"/-c \"\/sbin\/sulogin; /g" /usr/lib/systemd/system/rescue.service
    fi

#### Disable debug-shell SystemD Service [ref]rule

SystemD's `debug-shell` service is intended to diagnose SystemD related boot issues with various `systemctl` commands. Once enabled and following a system reboot, the root shell will be available on `tty9` which is access by pressing `CTRL-ALT-F9`. The `debug-shell` service should only be used for SystemD related issues and should otherwise be disabled.
By default, the `debug-shell` SystemD service is disabled. The `debug-shell` service can be disabled with the following command:

    $ sudo systemctl disable debug-shell.service

Rationale:

This prevents attackers with physical access from trivially bypassing security on the machine through valid troubleshooting configurations and gaining root access when the system is rebooted.

Severity: medium

Identifiers: CCE-80206-6

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

    service_command disable debug-shell

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Disable service debug-shell
      service:
        name="{{item}}"
        enabled="no"
        state="stopped"
      with_items:
        - debug-shell

#### Disable Ctrl-Alt-Del Reboot Activation [ref]rule

By default, `SystemD` will reboot the system if the `Ctrl-Alt-Del` key sequence is pressed.
To configure the system to ignore the `Ctrl-Alt-Del` key sequence from the command line instead of rebooting the system, do either of the following:

    ln -sf /dev/null /etc/systemd/system/ctrl-alt-del.target

or

    systemctl mask ctrl-alt-del.target

Do not simply delete the `/usr/lib/systemd/system/ctrl-alt-del.service` file, as this file may be restored during future system updates.
Warning: Disabling the `Ctrl-Alt-Del` key sequence with `SystemD` DOES NOT disable the `Ctrl-Alt-Del` key sequence if running in `graphical.target` mode (e.g. in GNOME, KDE, etc.)! The `Ctrl-Alt-Del` key sequence will only be disabled if running in the non-graphical `multi-user.target` mode.
Rationale:

A locally logged-in user who presses Ctrl-Alt-Del, when at the console, can reboot the system. If accidentally pressed, as could happen in the case of mixed OS environment, this can create the risk of short-term loss of availability of systems due to unintentional reboot.

Severity: high

Identifiers: CCE-27511-5

References: AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-020220

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # The process to disable ctrl+alt+del has changed in RHEL7.
    # Reference: https://access.redhat.com/solutions/1123873
    ln -sf /dev/null /etc/systemd/system/ctrl-alt-del.target

#### Verify that Interactive Boot is Disabled [ref]rule

Red Hat Enterprise Linux systems support an "interactive boot" option that can be used to prevent services from being started. On a Red Hat Enterprise Linux 7 system, interactive boot can be enabled by providing a `1`, `yes`, `true`, or `on` value to the `systemd.confirm_spawn` kernel argument in `/etc/default/grub`. Remove any instance of

    systemd.confirm_spawn=(1|yes|true|on)

from the kernel arguments in that file to disable interactive boot.
Warning: The GRUB 2 configuration file, `grub.cfg`, is automatically updated each time a new kernel is installed. Note that any changes to `/etc/default/grub` require rebuilding the `grub.cfg` file. To update the GRUB 2 configuration file manually, use the

    grub2-mkconfig -o

command as follows:

- On BIOS-based machines, issue the following command as `root`:

      ~]# grub2-mkconfig -o /boot/grub2/grub.cfg

- On UEFI-based machines, issue the following command as `root`:

      ~]# grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

Rationale:

Using interactive boot, the console user could disable auditing, firewalls, or other services, weakening system security.

Severity: medium

Identifiers: CCE-27335-9

References: SC-2, AC-3, 213

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Systemd confirm_spawn regex to search for and delete if found
    CONFIRM_SPAWN_REGEX="systemd.confirm_spawn=\(1\|yes\|true\|on\)"

    # Modify both the GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT directives
    for grubcmdline in "GRUB_CMDLINE_LINUX" "GRUB_CMDLINE_LINUX_DEFAULT"
    do
      # Remove 'systemd.confirm_spawn' argument from /etc/default/grub if found
      if grep -q "^${grubcmdline}=\".*${CONFIRM_SPAWN_REGEX}.*\"" /etc/default/grub
      then
        # Remove all three possible occurrences of CONFIRM_SPAWN_REGEX:
        # At the start
        sed -i "s/\"${CONFIRM_SPAWN_REGEX} /\"/" /etc/default/grub
        # At the end
        sed -i "s/ ${CONFIRM_SPAWN_REGEX}\"$/\"/" /etc/default/grub
        # In the middle
        sed -i "s/ ${CONFIRM_SPAWN_REGEX}//" /etc/default/grub
      fi
    done
    # Remove 'systemd.confirm_spawn' kernel argument also from runtime settings
    /sbin/grubby --update-kernel=ALL --remove-args="systemd.confirm_spawn"

### Warning Banners for System Accesses [ref]group

Each system should expose as little information about itself as possible.
System banners, which are typically displayed just before a login prompt, give out information about the service or the host's operating system. This might include the distribution name and the system kernel version, and the particular version of a network service. This information can assist intruders in gaining access to the system as it can reveal whether the system is running vulnerable software. Most network services can be configured to limit what information is displayed.
Many organizations implement security policies that require a system banner provide notice of the system's ownership, provide warning to unauthorized users, and remind authorized users of their consent to monitoring.

contains 3 rules

### Implement a GUI Warning Banner [ref]group

In the default graphical environment, users logging directly into the system are greeted with a login screen provided by the GNOME3 Display Manager (GDM). The warning banner should be displayed in this graphical environment for these users. The following sections describe how to configure the GDM login banner.

contains 2 rules

#### Enable GNOME3 Login Warning Banner [ref]rule

To enable displaying a login warning banner in the GNOME Display Manager's login screen, the `banner-message-enable` setting must be set under an appropriate configuration file(s) in the `/etc/dconf/db/gdm.d` directory and locked in `/etc/dconf/db/gdm.d/locks` directory to prevent user modification. After the settings have been set, run `dconf update`. To display a banner, this setting must be enabled, and the user must be prevented from making changes. The banner text must also be set.

Rationale:

Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance. For U.S. Government systems, system use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist.

Severity: medium

Identifiers: CCE-26970-4

References: AC-8(a), AC-8(b), AC-8(c)(1), AC-8(c)(2), AC-8(c)(3), 48, OS-SRG-000023-GPOS-00006, SRG-OS-000024-GPOS-00007, SRG-OS-000228-GPOS-00088, RHEL-07-010030

#### Set the GNOME3 Login Warning Banner Text [ref]rule

To set the text shown by the GNOME3 Display Manager in the login screen, the `banner-message-text` setting must be set under an appropriate configuration file(s) in the `/etc/dconf/db/gdm.d` directory and locked in `/etc/dconf/db/gdm.d/locks` directory to prevent user modification. After the settings have been set, run `dconf update`. When entering a warning banner that spans several lines, remember to begin and end the string with `'` and use `\n` for new lines.

Rationale:

An appropriate warning message reinforces policy awareness during the logon process and facilitates possible legal action against attackers.

Severity: medium

Identifiers: CCE-26892-0

References: AC-8(a), AC-8(b), AC-8(c), 48, SRG-OS-000023-GPOS-00006, SRG-OS-000024-GPOS-00007, SRG-OS-000228-GPOS-00088, RHEL-07-010031

#### Modify the System Login Banner [ref]rule

To configure the system login banner edit `/etc/issue`. Replace the default text with a message compliant with the local site policy or a legal disclaimer. The DoD required text is either:
`You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only. By using this IS (which includes any device attached to this IS), you consent to the following conditions:
-The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations.
-At any time, the USG may inspect and seize data stored on this IS.
-Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose.
-This IS includes security measures (e.g., authentication and access controls) to protect USG interests -- not for your personal benefit or privacy.
-Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details.`
OR:
`I've read & consent to terms in IS user agreem't.`

Rationale:

Display of a standardized and approved use notification before granting access to the operating system ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance. System use notifications are required only for access via login interfaces with human users and are not required when such human interfaces do not exist.

Severity: medium

Identifiers: CCE-27303-7

References: AC-8(a), AC-8(b), AC-8(c)(1), AC-8(c)(2), AC-8(c)(3), 48, SRG-OS-000023-GPOS-00006, SRG-OS-000024-GPOS-00007, RHEL-07-010040

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    login_banner_text="You[\s\n]+are[\s\n]+accessing[\s\n]+a[\s\n]+U.S.[\s\n]+Government[\s\n]+\(USG\)[\s\n]+Information[\s\n]+System[\s\n]+\(IS\)[\s\n]+that[\s\n]+is[\s\n]+provided[\s\n]+for[\s\n]+USG-authorized[\s\n]+use[\s\n]+only.[\s\n]*By[\s\n]+using[\s\n]+this[\s\n]+IS[\s\n]+\(which[\s\n]+includes[\s\n]+any[\s\n]+device[\s\n]+attached[\s\n]+to[\s\n]+this[\s\n]+IS\),[\s\n]+you[\s\n]+consent[\s\n]+to[\s\n]+the[\s\n]+following[\s\n]+conditions\:[\s\n]*-[\s\n]*The[\s\n]+USG[\s\n]+routinely[\s\n]+intercepts[\s\n]+and[\s\n]+monitors[\s\n]+communications[\s\n]+on[\s\n]+this[\s\n]+IS[\s\n]+for[\s\n]+purposes[\s\n]+including,[\s\n]+but[\s\n]+not[\s\n]+limited[\s\n]+to,[\s\n]+penetration[\s\n]+testing,[\s\n]+COMSEC[\s\n]+monitoring,[\s\n]+network[\s\n]+operations[\s\n]+and[\s\n]+defense,[\s\n]+personnel[\s\n]+misconduct[\s\n]+\(PM\),[\s\n]+law[\s\n]+enforcement[\s\n]+\(LE\),[\s\n]+and[\s\n]+counterintelligence[\s\n]+\(CI\)[\s\n]+investigations.[\s\n]*-[\s\n]*At[\s\n]+any[\s\n]+time,[\s\n]+the[\s\n]+USG[\s\n]+may[\s\n]+inspect[\s\n]+and[\s\n]+seize[\s\n]+data[\s\n]+stored[\s\n]+on[\s\n]+this[\s\n]+IS.[\s\n]*-[\s\n]*Communications[\s\n]+using,[\s\n]+or[\s\n]+data[\s\n]+stored[\s\n]+on,[\s\n]+this[\s\n]+IS[\s\n]+are[\s\n]+not[\s\n]+private,[\s\n]+are[\s\n]+subject[\s\n]+to[\s\n]+routine[\s\n]+monitoring,[\s\n]+interception,[\s\n]+and[\s\n]+search,[\s\n]+and[\s\n]+may[\s\n]+be[\s\n]+disclosed[\s\n]+or[\s\n]+used[\s\n]+for[\s\n]+any[\s\n]+USG-authorized[\s\n]+purpose.[\s\n]*-[\s\n]*This[\s\n]+IS[\s\n]+includes[\s\n]+security[\s\n]+measures[\s\n]+\(e.g.,[\s\n]+authentication[\s\n]+and[\s\n]+access[\s\n]+controls\)[\s\n]+to[\s\n]+protect[\s\n]+USG[\s\n]+interests[\s\n]+--[\s\n]+not[\s\n]+for[\s\n]+your[\s\n]+personal[\s\n]+benefit[\s\n]+or[\s\n]+privacy.[\s\n]*-[\s\n]*Notwithstanding[\s\n]+the[\s\n]+above,[\s\n]+using[\s\n]+this[\s\n]+IS[\s\n]+does[\s\n]+not[\s\n]+constitute[\s\n]+consent[\s\n]+to[\s\n]+PM,[\s\n]+LE[\s\n]+or[\s\n]+CI[\s\n]+investigative[\s\n]+searching[\s\n]+or[\s\n]+monitoring[\s\n]+of[\s\n]+the[\s\n]+content[\s\n]+of[\s\n]+privileged[\s\n]+communications,[\s\n]+or[\s\n]+work[\s\n]+product,[\s\n]+related[\s\n]+to[\s\n]+personal[\s\n]+representation[\s\n]+or[\s\n]+services[\s\n]+by[\s\n]+attorneys,[\s\n]+psychotherapists,[\s\n]+or[\s\n]+clergy,[\s\n]+and[\s\n]+their[\s\n]+assistants.[\s\n]+Such[\s\n]+communications[\s\n]+and[\s\n]+work[\s\n]+product[\s\n]+are[\s\n]+private[\s\n]+and[\s\n]+confidential.[\s\n]+See[\s\n]+User[\s\n]+Agreement[\s\n]+for[\s\n]+details."

    # There was a regular-expression matching various banners, needs to be expanded
    expanded=$(echo "$login_banner_text" | sed 's/\[\\s\\n\][+*]/ /g;s/\\//g;s/[^-]- /\n\n-/g')
    formatted=$(echo "$expanded" | fold -sw 80)

    cat <<EOF >/etc/issue
    $formatted
    EOF

    printf "\n" >> /etc/issue

### Network Configuration and Firewalls [ref]group

Most machines must be connected to a network of some sort, and this brings with it the substantial risk of network attack. This section discusses the security impact of decisions about networking which must be made when configuring a system.
This section also discusses firewalls, network access controls, and other network security frameworks, which allow system-level rules to be written that can limit an attackers' ability to connect to your system. These rules can specify that network traffic should be allowed or denied from certain IP addresses, hosts, and networks. The rules can also specify which of the system's network services are available to particular hosts or networks.

contains 20 rules

### Kernel Parameters Which Affect Networking [ref]group

The `sysctl` utility is used to set parameters which affect the operation of the Linux kernel. Kernel parameters which affect networking and have security implications are described here.

contains 9 rules

### Network Parameters for Hosts Only [ref]group

If the system is not going to be used as a router, then setting certain kernel parameters ensure that the host will not perform routing of network traffic.

contains 3 rules

#### Disable Kernel Parameter for Sending ICMP Redirects by Default [ref]rule

To set the runtime status of the `net.ipv4.conf.default.send_redirects` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.conf.default.send_redirects=0

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    net.ipv4.conf.default.send_redirects = 0

Rationale:

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages contain information from the system's route table possibly revealing portions of the network topology.
The ability to send ICMP redirects is only appropriate for systems acting as routers.

Severity: medium

Identifiers: CCE-80156-3

References: AC-4, CM-7, SC-5, SC-7, 366, 4.1.2, SRG-OS-000480-GPOS-00227, RHEL-07-040420

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    #
    # Set runtime for net.ipv4.conf.default.send_redirects
    #
    /sbin/sysctl -q -n -w net.ipv4.conf.default.send_redirects=0

    #
    # If net.ipv4.conf.default.send_redirects present in /etc/sysctl.conf, change value to "0"
    #	else, add "net.ipv4.conf.default.send_redirects = 0" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.conf.default.send_redirects /etc/sysctl.conf ; then
    	sed -i 's/^net.ipv4.conf.default.send_redirects.*/net.ipv4.conf.default.send_redirects = 0/g' /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.conf.default.send_redirects to 0 per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.conf.default.send_redirects = 0" >> /etc/sysctl.conf
    fi

#### Disable Kernel Parameter for Sending ICMP Redirects for All Interfaces [ref]rule

To set the runtime status of the `net.ipv4.conf.all.send_redirects` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.conf.all.send_redirects=0

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    net.ipv4.conf.all.send_redirects = 0

Rationale:

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages contain information from the system's route table possibly revealing portions of the network topology.
The ability to send ICMP redirects is only appropriate for systems acting as routers.

Severity: medium

Identifiers: CCE-80156-3

References: AC-4, CM-7, SC-5(1), 366, 4.1.2, SRG-OS-000480-GPOS-00227, RHEL-07-040421

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    #
    # Set runtime for net.ipv4.conf.all.send_redirects
    #
    /sbin/sysctl -q -n -w net.ipv4.conf.all.send_redirects=0

    #
    # If net.ipv4.conf.all.send_redirects present in /etc/sysctl.conf, change value to "0"
    #	else, add "net.ipv4.conf.all.send_redirects = 0" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.conf.all.send_redirects /etc/sysctl.conf ; then
    	sed -i 's/^net.ipv4.conf.all.send_redirects.*/net.ipv4.conf.all.send_redirects = 0/g' /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.conf.all.send_redirects to 0 per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.conf.all.send_redirects = 0" >> /etc/sysctl.conf
    fi

#### Disable Kernel Parameter for IP Forwarding [ref]rule

To set the runtime status of the `net.ipv4.ip_forward` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.ip_forward=0

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    net.ipv4.ip_forward = 0

Rationale:

Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If this capability is used when not required, system network information may be unnecessarily transmitted across the network.

Severity: medium

Identifiers: CCE-80157-1

References: CM-7, SC-5, SC-32, 366, 4.1.1, SRG-OS-000480-GPOS-00227, RHEL-07-040730

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    #
    # Set runtime for net.ipv4.ip_forward
    #
    /sbin/sysctl -q -n -w net.ipv4.ip_forward=0

    #
    # If net.ipv4.ip_forward present in /etc/sysctl.conf, change value to "0"
    #	else, add "net.ipv4.ip_forward = 0" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.ip_forward /etc/sysctl.conf ; then
    	sed -i 's/^net.ipv4.ip_forward.*/net.ipv4.ip_forward = 0/g' /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.ip_forward to 0 per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.ip_forward = 0" >> /etc/sysctl.conf
    fi

### Network Related Kernel Runtime Parameters for Hosts and Routers [ref]group

Certain kernel parameters should be set for systems which are acting as either hosts or routers to improve the system's ability defend against certain types of IPv4 protocol attacks.

contains 6 rules

#### Configure Kernel Parameter for Accepting Source-Routed Packets for All Interfaces [ref]rule

To set the runtime status of the `net.ipv4.conf.all.accept_source_route` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.conf.all.accept_source_route=0

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    net.ipv4.conf.all.accept_source_route = 0

Rationale:

Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routerd traffic, such as when IPv4 forwarding is enabled and the system is functioning as a router.
Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required.

Severity: medium

Identifiers: CCE-27434-0

References: AC-4, CM-7, SC-5, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040350, 4.2.1

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    sysctl_net_ipv4_conf_all_accept_source_route_value="0"

    #
    # Set runtime for net.ipv4.conf.all.accept_source_route
    #
    /sbin/sysctl -q -n -w net.ipv4.conf.all.accept_source_route=$sysctl_net_ipv4_conf_all_accept_source_route_value

    #
    # If net.ipv4.conf.all.accept_source_route present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.conf.all.accept_source_route = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.conf.all.accept_source_route /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.conf.all.accept_source_route.*/net.ipv4.conf.all.accept_source_route = $sysctl_net_ipv4_conf_all_accept_source_route_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.conf.all.accept_source_route to $sysctl_net_ipv4_conf_all_accept_source_route_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.conf.all.accept_source_route = $sysctl_net_ipv4_conf_all_accept_source_route_value" >> /etc/sysctl.conf
    fi

#### Configure Kernel Parameter for Accepting ICMP Redirects for All Interfaces [ref]rule

To set the runtime status of the `net.ipv4.conf.all.accept_redirects` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.conf.all.accept_redirects=0

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    net.ipv4.conf.all.accept_redirects = 0

Rationale:

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack.
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required.

Severity: medium

Identifiers: CCE-80158-9

References: CM-6(d), CM-7, SC-5, 366, 1503, 1551, 4.2.2, SRG-OS-000480-GPOS-00227, RHEL-07-040410

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    sysctl_net_ipv4_conf_all_accept_redirects_value="0"

    #
    # Set runtime for net.ipv4.conf.all.accept_redirects
    #
    /sbin/sysctl -q -n -w net.ipv4.conf.all.accept_redirects=$sysctl_net_ipv4_conf_all_accept_redirects_value

    #
    # If net.ipv4.conf.all.accept_redirects present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.conf.all.accept_redirects = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.conf.all.accept_redirects /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.conf.all.accept_redirects.*/net.ipv4.conf.all.accept_redirects = $sysctl_net_ipv4_conf_all_accept_redirects_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.conf.all.accept_redirects to $sysctl_net_ipv4_conf_all_accept_redirects_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.conf.all.accept_redirects = $sysctl_net_ipv4_conf_all_accept_redirects_value" >> /etc/sysctl.conf
    fi

#### Configure Kernel Parameter for Accepting Source-Routed Packets By Default [ref]rule

To set the runtime status of the `net.ipv4.conf.default.accept_source_route` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.conf.default.accept_source_route=0

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    net.ipv4.conf.default.accept_source_route = 0

Rationale:

Source-routed packates allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures.
Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required, such as when IPv4 forwarding is enabled and the system is legitimately functioning as a router.

Severity: medium

Identifiers: CCE-80162-1

References: AC-4, CM-7, SC-5, SC-7, 366, 1551, SRG-OS-000480-GPOS-00227, RHEL-07-040351, 4.2.1

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    sysctl_net_ipv4_conf_default_accept_source_route_value="0"

    #
    # Set runtime for net.ipv4.conf.default.accept_source_route
    #
    /sbin/sysctl -q -n -w net.ipv4.conf.default.accept_source_route=$sysctl_net_ipv4_conf_default_accept_source_route_value

    #
    # If net.ipv4.conf.default.accept_source_route present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.conf.default.accept_source_route = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.conf.default.accept_source_route /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.conf.default.accept_source_route.*/net.ipv4.conf.default.accept_source_route = $sysctl_net_ipv4_conf_default_accept_source_route_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.conf.default.accept_source_route to $sysctl_net_ipv4_conf_default_accept_source_route_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.conf.default.accept_source_route = $sysctl_net_ipv4_conf_default_accept_source_route_value" >> /etc/sysctl.conf
    fi

#### Configure Kernel Parameter for Accepting ICMP Redirects By Default [ref]rule

To set the runtime status of the `net.ipv4.conf.default.accept_redirects` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.conf.default.accept_redirects=0

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    net.ipv4.conf.default.accept_redirects = 0

Rationale:

ICMP redirect messages are used by routers to inform hosts that a more direct route exists for a particular destination. These messages modify the host's route table and are unauthenticated. An illicit ICMP redirect message could result in a man-in-the-middle attack.
This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless absolutely required.

Severity: medium

Identifiers: CCE-80163-9

References: AC-4, CM-7, SC-5, SC-7, 1551, 4.2.2, SRG-OS-000480-GPOS-00227, RHEL-07-TBD

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    sysctl_net_ipv4_conf_default_accept_redirects_value="0"

    #
    # Set runtime for net.ipv4.conf.default.accept_redirects
    #
    /sbin/sysctl -q -n -w net.ipv4.conf.default.accept_redirects=$sysctl_net_ipv4_conf_default_accept_redirects_value

    #
    # If net.ipv4.conf.default.accept_redirects present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.conf.default.accept_redirects = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.conf.default.accept_redirects /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.conf.default.accept_redirects.*/net.ipv4.conf.default.accept_redirects = $sysctl_net_ipv4_conf_default_accept_redirects_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.conf.default.accept_redirects to $sysctl_net_ipv4_conf_default_accept_redirects_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.conf.default.accept_redirects = $sysctl_net_ipv4_conf_default_accept_redirects_value" >> /etc/sysctl.conf
    fi

#### Configure Kernel Parameter to Ignore ICMP Broadcast Echo Requests [ref]rule

To set the runtime status of the `net.ipv4.icmp_echo_ignore_broadcasts` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    net.ipv4.icmp_echo_ignore_broadcasts = 1

Rationale:

Responding to broadcast (ICMP) echoes facilitates network mapping and provides a vector for amplification attacks.
Ignoring ICMP echo requests (pings) sent to broadcast or multicast addresses makes the system slightly more difficult to enumerate on the network.

Severity: medium

Identifiers: CCE-80165-4

References: AC-4, CM-7, SC-5, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040380, 4.2.5

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value="1"

    #
    # Set runtime for net.ipv4.icmp_echo_ignore_broadcasts
    #
    /sbin/sysctl -q -n -w net.ipv4.icmp_echo_ignore_broadcasts=$sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value

    #
    # If net.ipv4.icmp_echo_ignore_broadcasts present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.icmp_echo_ignore_broadcasts = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.icmp_echo_ignore_broadcasts /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.icmp_echo_ignore_broadcasts.*/net.ipv4.icmp_echo_ignore_broadcasts = $sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.icmp_echo_ignore_broadcasts to $sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.icmp_echo_ignore_broadcasts = $sysctl_net_ipv4_icmp_echo_ignore_broadcasts_value" >> /etc/sysctl.conf
    fi

#### Configure Kernel Parameter to Use TCP Syncookies [ref]rule

To set the runtime status of the `net.ipv4.tcp_syncookies` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.tcp_syncookies=1

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    net.ipv4.tcp_syncookies = 1

Rationale:

A TCP SYN flood attack can cause a denial of service by filling a system's TCP connection table with connections in the SYN_RCVD state. Syncookies can be used to track a connection when a subsequent ACK is received, verifying the initiator is attempting a valid connection and is not a flood source. This feature is activated when a flood condition is detected, and enables the system to continue servicing valid connection requests.

Severity: medium

Identifiers: CCE-27495-1

References: AC-4, SC-5(1)(2), SC-5(2), SC-5(3), 366, SRG-OS-000480-GPOS-00227, RHEL-07-040430, 4.2.8

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    sysctl_net_ipv4_tcp_syncookies_value="1"

    #
    # Set runtime for net.ipv4.tcp_syncookies
    #
    /sbin/sysctl -q -n -w net.ipv4.tcp_syncookies=$sysctl_net_ipv4_tcp_syncookies_value

    #
    # If net.ipv4.tcp_syncookies present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.tcp_syncookies = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.tcp_syncookies /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.tcp_syncookies.*/net.ipv4.tcp_syncookies = $sysctl_net_ipv4_tcp_syncookies_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.tcp_syncookies to $sysctl_net_ipv4_tcp_syncookies_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.tcp_syncookies = $sysctl_net_ipv4_tcp_syncookies_value" >> /etc/sysctl.conf
    fi

### Wireless Networking [ref]group

Wireless networking, such as 802.11 (WiFi) and Bluetooth, can present a security risk to sensitive or classified systems and networks. Wireless networking hardware is much more likely to be included in laptop or portable systems than in desktops or servers.
Removal of hardware provides the greatest assurance that the wireless capability remains disabled. Acquisition policies often include provisions to prevent the purchase of equipment that will be used in sensitive spaces and includes wireless capabilities. If it is impractical to remove the wireless hardware, and policy permits the device to enter sensitive spaces as long as wireless is disabled, efforts should instead focus on disabling wireless capability via software.

contains 4 rules

### Disable Wireless Through Software Configuration [ref]group

If it is impossible to remove the wireless hardware from the device in question, disable as much of it as possible through software. The following methods can disable software support for wireless networking, but note that these methods do not prevent malicious software or careless users from re-activating the devices.

contains 4 rules

#### Disable WiFi or Bluetooth in BIOS [ref]rule

Some systems that include built-in wireless support offer the ability to disable the device through the BIOS. This is system-specific; consult your hardware manual or explore the BIOS setup during boot.

Rationale:

Disabling wireless support in the BIOS prevents easy activation of the wireless interface, generally requiring administrators to reboot the system first.

Severity: low

Identifiers: CCE-27397-9

References: AC-17(8), AC-18(a), AC-18(d), AC-18(3), CM-7, 85

#### Deactivate Wireless Network Interfaces [ref]rule

Deactivating wireless network interfaces should prevent normal usage of the wireless capability.
First, identify the interfaces available with the command:

    $ ifconfig -a

Additionally, the following command may be used to determine whether wireless support is included for a particular interface, though this may not always be a clear indicator:

    $ iwconfig

After identifying any wireless interfaces (which may have names like `wlan0`, `ath0`, `wifi0`, `em1` or `eth0`), deactivate the interface with the command:

    $ sudo ifdown interface

These changes will only last until the next reboot. To disable the interface for future boots, remove the appropriate interface file from `/etc/sysconfig/network-scripts`:

    $ sudo rm /etc/sysconfig/network-scripts/ifcfg-interface

Rationale:

Wireless networking allows attackers within physical proximity to launch network-based attacks against systems, including those against local LAN protocols which were not designed with security in mind.

Severity: low

Identifiers: CCE-27358-1

References: AC-17(8), AC-18(a), AC-18(d), AC-18(3), CM-7, 85, 4.3.1

#### Disable Bluetooth Service [ref]rule

The `bluetooth` service can be disabled with the following command:

    $ sudo systemctl disable bluetooth.service

    $ sudo service bluetooth stop

Rationale:

Disabling the `bluetooth` service prevents the system from attempting connections to Bluetooth devices, which entails some security risk. Nevertheless, variation in this risk decision may be expected due to the utility of Bluetooth connectivity and its limited range.

Severity: medium

Identifiers: CCE-27328-4

References: AC-17(8), AC-18(a), AC-18(d), AC-18(3), CM-7, 85, 1551

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    grep -qi disable /etc/xinetd.d/bluetooth && \
    	sed -i 's/disable.*/disable	= yes/gI' /etc/xinetd.d/bluetooth
    #
    # Disable bluetooth.service for all systemd targets
    #
    systemctl disable bluetooth.service

    #
    # Stop bluetooth.service if currently running
    #
    systemctl stop bluetooth.service

#### Disable Bluetooth Kernel Modules [ref]rule

The kernel's module loading system can be configured to prevent loading of the Bluetooth module. Add the following to the appropriate `/etc/modprobe.d` configuration file to prevent the loading of the Bluetooth module:

    install bluetooth /bin/true

Rationale:

If Bluetooth functionality must be disabled, preventing the kernel from loading the kernel module provides an additional safeguard against its activation.

Severity: medium

Identifiers: CCE-27327-6

References: AC-17(8), AC-18(a), AC-18(d), AC-18(3), CM-7, 85, 1551

Remediation Shell script: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    if grep --silent "^install bluetooth" /etc/modprobe.d/bluetooth.conf ; then
            sed -i 's/^install bluetooth.*/install bluetooth /bin/true/g' /etc/modprobe.d/bluetooth.conf
    else
            echo -e "\n# Disable per security requirements" >> /etc/modprobe.d/bluetooth.conf
            echo "install bluetooth /bin/true" >> /etc/modprobe.d/bluetooth.conf
    fi

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | medium
Reboot: | true
Strategy: | disable

    - name: Ensure kernel module 'bluetooth' is disabled
      lineinfile:
        create=yes
        dest="/etc/modprobe.d/{{item}}.conf"
        regexp="{{item}}"
        line="install {{item}} /bin/true"
      with_items:
        - bluetooth

### IPv6 [ref]group

The system includes support for Internet Protocol version 6. A major and often-mentioned improvement over IPv4 is its enormous increase in the number of available addresses. Another important feature is its support for automatic configuration of many network settings.

contains 1 rule

### Configure IPv6 Settings if Necessary [ref]group

A major feature of IPv6 is the extent to which systems implementing it can automatically configure their networking devices using information from the network. From a security perspective, manually configuring important configuration information is preferable to accepting it from the network in an unauthenticated fashion.

contains 1 rule

### Disable Automatic Configuration [ref]group

Disable the system's acceptance of router advertisements and redirects by adding or correcting the following line in `/etc/sysconfig/network` (note that this does not disable sending router solicitations):

    IPV6_AUTOCONF=no

contains 1 rule

#### Configure Kernel Parameter for Accepting Source-Routed Packets for All Interfaces [ref]rule

To set the runtime status of the `net.ipv6.conf.all.accept_source_route` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv6.conf.all.accept_source_route=0

If this is not the system's default value, add the following line to `/etc/sysctl.conf`:

    net.ipv6.conf.all.accept_source_route = 0

Rationale:

Source-routed packets allow the source of the packet to suggest routers forward the packet along a different path than configured on the router, which can be used to bypass network security measures. This requirement applies only to the forwarding of source-routerd traffic, such as when IPv6 forwarding is enabled and the system is functioning as a router.
Accepting source-routed packets in the IPv6 protocol has few legitimate uses. It should be disabled unless it is absolutely required.

Severity: medium

Identifiers: CCE-80179-5

References: AC-4, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040860

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    #
    # Set runtime for SYSCTLVAR
    #
    /sbin/sysctl -q -n -w net.ipv6.conf.all.accept_source_route=0

    #
    # If SYSCTLVAR present in /etc/sysctl.conf, change value to "SYSCTLVAL"
    #	else, add "SYSCTLVAR = SYSCTLVAL" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv6.conf.all.accept_source_route /etc/sysctl.conf ; then
    	sed -i 's/^net.ipv6.conf.all.accept_source_route.*/net.ipv6.conf.all.accept_source_route = 0/g' /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv6.conf.all.accept_source_route to 0 per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv6.conf.all.accept_source_route = 0" >> /etc/sysctl.conf
    fi

### firewalld [ref]group

The dynamic firewall daemon `firewalld` provides a dynamically managed firewall with support for network “zones” to assign a level of trust to a network and its associated connections and interfaces. It has support for IPv4 and IPv6 firewall settings. It supports Ethernet bridges and has a separation of runtime and permanent configuration options. It also has an interface for services or applications to add firewall rules directly.
A graphical configuration tool, `firewall-config`, is used to configure `firewalld`, which in turn uses `iptables` tool to communicate with `Netfilter` in the kernel which implements packet filtering.
The firewall service provided by `firewalld` is dynamic rather than static because changes to the configuration can be made at anytime and are immediately implemented. There is no need to save or apply the changes. No unintended disruption of existing network connections occurs as no part of the firewall has to be reloaded.

contains 2 rules

### Inspect and Activate Default firewalld Rules [ref]group

Firewalls can be used to separate networks into different zones based on the level of trust the user has decided to place on the devices and traffic within that network. `NetworkManager` informs firewalld to which zone an interface belongs. An interface's assigned zone can be changed by `NetworkManager` or via the `firewall-config` tool.
The zone settings in `/etc/firewalld/` are a range of preset settings which can be quickly applied to a network interface. These are the zones provided by firewalld sorted according to the default trust level of the zones from untrusted to trusted:

- `drop`

  Any incoming network packets are dropped, there is no reply. Only outgoing network connections are possible.

- `block`

  Any incoming network connections are rejected with an `icmp-host-prohibited` message for IPv4 and `icmp6-adm-prohibited` for IPv6. Only network connections initiated from within the system are possible.

- `public`

  For use in public areas. You do not trust the other computers on the network to not harm your computer. Only selected incoming connections are accepted.

- `external`

  For use on external networks with masquerading enabled especially for routers. You do not trust the other computers on the network to not harm your computer. Only selected incoming connections are accepted.

- `dmz`

  For computers in your demilitarized zone that are publicly-accessible with limited access to your internal network. Only selected incoming connections are accepted.

- `work`

  For use in work areas. You mostly trust the other computers on networks to not harm your computer. Only selected incoming connections are accepted.

- `home`

  For use in home areas. You mostly trust the other computers on networks to not harm your computer. Only selected incoming connections are accepted.

- `internal`

  For use on internal networks. You mostly trust the other computers on the networks to not harm your computer. Only selected incoming connections are accepted.

- `trusted`

  All network connections are accepted.

It is possible to designate one of these zones to be the default zone. When interface connections are added to `NetworkManager`, they are assigned to the default zone. On installation, the default zone in firewalld is set to be the public zone.
To find out all the settings of a zone, for example the `public zone,` enter the following command as root:

    # firewall-cmd --zone=public --list-all

Example output of this command might look like the following:

    # firewall-cmd --zone=public --list-all
    public
      interfaces:
      services: mdns dhcpv6-client ssh
      ports:
      forward-ports:
      icmp-blocks: source-quench

To view the network zones currently active, enter the following command as root:

    # firewall-cmd --get-service

The following listing displays the result of this command on common Red Hat Enterprise Linux 7 Server system:

    # firewall-cmd --get-service
    amanda-client bacula bacula-client dhcp dhcpv6 dhcpv6-client dns ftp
    high-availability http https imaps ipp ipp-client ipsec kerberos kpasswd
    ldap ldaps libvirt libvirt-tls mdns mountd ms-wbt mysql nfs ntp openvpn
    pmcd pmproxy pmwebapi pmwebapis pop3s postgresql proxy-dhcp radius rpc-bind
    samba samba-client smtp ssh telnet tftp tftp-client transmission-client
    vnc-server wbem-https

Finally to view the network zones that will be active after the next firewalld service reload, enter the following command as root:

    # firewall-cmd --get-service --permanent

contains 1 rule

#### Verify firewalld Enabled [ref]rule

The `firewalld` service can be enabled with the following command:

    $ sudo systemctl enable firewalld.service

Rationale:

Access control methods provide the ability to enhance system security posture by restricting services and known good IP addresses and address ranges. This prevents connections from unknown hosts and protocols.

Severity: medium

Identifiers: CCE-27361-5

References: CM-6(b), 366, 4.7, SRG-OS-000480-GPOS-00227, RHEL-07-040810

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

    service_command enable firewalld

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    - name: Enable service firewalld
      service:
        name="{{item}}"
        enabled="yes"
        state="started"
      with_items:
        - firewalld

### Strengthen the Default Ruleset [ref]group

The default rules can be strengthened. The system scripts that activate the firewall rules expect them to be defined in configuration files under the `/etc/firewalld/services` and `/etc/firewalld/zones` directories.
The following recommendations describe how to strengthen the default ruleset configuration file. An alternative to editing this configuration file is to create a shell script that makes calls to the `firewall-cmd` program to load in rules under the `/etc/firewalld/services` and `/etc/firewalld/zones` directories.
Instructions apply to both unless otherwise noted. Language and address conventions for regular firewalld rules are used throughout this section.

Warning: The program `firewall-config` allows additional services to penetrate the default firewall rules and automatically adjusts the `firewalld` ruleset(s).

contains 1 rule

#### Set Default firewalld Zone for Incoming Packets [ref]rule

To set the default zone to `drop` for the built-in default zone which processes incoming IPv4 and IPv6 packets, modify the following line in `/etc/firewalld/firewalld.conf` to be:

    DefaultZone=drop

Rationale:

In `firewalld` the default zone is applied only after all the applicable rules in the table are examined for a match. Setting the default zone to `drop` implements proper design for a firewall, i.e. any packets which are not explicitly permitted should not be accepted.

Severity: medium

Identifiers: CCE-27349-0

References: CM-6(b), CM-7, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040820

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    grep -q ^DefaultZone= /etc/firewalld/firewalld.conf && \
      sed -i "s/DefaultZone=.*/DefaultZone=drop/g" /etc/firewalld/firewalld.conf
    if ! [ $? -eq 0 ]; then
        echo "DefaultZone=drop" >> /etc/firewalld/firewalld.conf
    fi

### IPSec Support [ref]group

Support for Internet Protocol Security (IPsec) is provided in Red Hat Enterprise Linux 7 with Libreswan.

contains 2 rules

#### Install libreswan Package [ref]rule

The Libreswan package provides an implementation of IPsec and IKE, which permits the creation of secure tunnels over untrusted networks. The `libreswan` package can be installed with the following command:

    $ sudo yum install libreswan

Rationale:

Providing the ability for remote users or systems to initiate a secure VPN connection protects information when it is transmitted over a wide area network.

Severity: medium

Identifiers: CCE-80170-4

References: AC-17, MA-4, SC-9, 1130, 1131, Req-4.1

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command install libreswan

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    - name: Ensure libreswan is installed
      package:
        name="{{item}}"
        state=present
      with_items:
        - libreswan

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    include install_libreswan

    class install_libreswan {
      package { 'libreswan':
        ensure => 'installed',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    package --add=libreswan

#### Verify Any Configured IPSec Tunnel Connections [ref]rule

Libreswan provides an implementation of IPsec and IKE, which permits the creation of secure tunnels over untrusted networks. As such, IPsec can be used to circumvent certain network requirements such as filtering. Verify that if any IPsec connection (`conn`) configured in `/etc/ipsec.conf` and `/etc/ipsec.d` exists is an approved organizational connection.

Rationale:

IP tunneling mechanisms can be used to bypass network filtering.

Severity: medium

Identifiers: CCE-80171-2

References: AC-4, 336, SRG-OS-000480-GPOS-00227, RHEL-07-040830

#### Disable Client Dynamic DNS Updates [ref]rule

Dynamic DNS allows clients to dynamically update their own DNS records. The updates are transmitted by unencrypted means which can reveal information to a potential malicious user. If the system does not require Dynamic DNS, remove all `DHCP_HOSTNAME` references from the `/etc/sysconfig/network-scripts/ifcfg-interface` scripts. If `dhclient` is used, remove all `send host-name hostname` references from the `/etc/dhclient.conf` configuration file and/or any reference from the `/etc/dhcp` directory.

Rationale:

Dynamic DNS updates transmit unencrypted information about a system including its name and address and should not be used unless needed.

Severity: medium

Identifiers: CCE-80357-7

References: CM-6(b), 366, SRG-OS-000480-GPOS-00227, RHEL-07-040840

#### Ensure System is Not Acting as a Network Sniffer [ref]rule

The system should not be acting as a network sniffer, which can capture all traffic on the network to which it is connected. Run the following to determine if any interface is running in promiscuous mode:

    $ ip link | grep PROMISC

Rationale:

Network interfaces in promiscuous mode allow for the capture of all network traffic visible to the system. If unauthorized individuals can access these applications, it may allow them to collect information such as logon IDs, passwords, and key exchanges between systems.
If the system is being used to perform a network troubleshooting function, the use of these tools must be documented with the Information Systems Security Manager (ISSM) and restricted to only authorized personnel.

Severity: medium

Identifiers: CCE-80174-6

References: CM-7, CM-7(2).1(i), http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-53r4.pdf, MA-3, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040470

### Configure Syslog [ref]group

The syslog service has been the default Unix logging mechanism for many years. It has a number of downsides, including inconsistent log format, lack of authentication for received messages, and lack of authentication, encryption, or reliable transport for messages sent over a network. However, due to its long history, syslog is a de facto standard which is supported by almost all Unix applications.
In Red Hat Enterprise Linux 7, rsyslog has replaced ksyslogd as the syslog daemon of choice, and it includes some additional security features such as reliable, connection-oriented (i.e. TCP) transmission of logs, the option to log to database formats, and the encryption of log data en route to a central logging server. This section discusses how to configure rsyslog for best effect, and how to use tools provided with the system to maintain and monitor logs.

contains 3 rules

### Ensure Proper Configuration of Log Files [ref]group

The file `/etc/rsyslog.conf` controls where log message are written. These are controlled by lines called rules, which consist of a selector and an action. These rules are often customized depending on the role of the system, the requirements of the environment, and whatever may enable the administrator to most effectively make use of log data. The default rules in Red Hat Enterprise Linux 7 are:

    *.info;mail.none;authpriv.none;cron.none                /var/log/messages
    authpriv.*                                              /var/log/secure
    mail.*                                                  -/var/log/maillog
    cron.*                                                  /var/log/cron
    *.emerg                                                 *
    uucp,news.crit                                          /var/log/spooler
    local7.*                                                /var/log/boot.log

See the man page `rsyslog.conf(5)` for more information. Note that the `rsyslog` daemon can be configured to use a timestamp format that some log processing programs may not understand. If this occurs, edit the file `/etc/rsyslog.conf` and add or edit the following line:

    $ ActionFileDefaultTemplate RSYSLOG_TraditionalFileFormat

contains 1 rule

#### Ensure cron Is Logging To Rsyslog [ref]rule

Cron logging must be implemented to spot intrusions or trace cron job status. If `cron` is not logging to `rsyslog`, it can be implemented by adding the following to the RULES section of `/etc/rsyslog.conf`:

    cron.*                                                  /var/log/cron

Rationale:

Cron logging can be used to trace the successful or unsuccessful execution of cron jobs. It can also be used to spot intrusions into the use of the cron facility by unauthorized and malicious users.

Severity: medium

Identifiers: CCE-80380-9

References: AU-2(d), 366, SRG-OS-000480-GPOS-00227, RHEL-07-021160

### Rsyslog Logs Sent To Remote Host [ref]group

If system logs are to be useful in detecting malicious activities, it is necessary to send logs to a remote server. An intruder who has compromised the root account on a machine may delete the log entries which indicate that the system was attacked before they are seen by an administrator.
However, it is recommended that logs be stored on the local host in addition to being sent to the loghost, especially if `rsyslog` has been configured to use the UDP protocol to send messages over a network. UDP does not guarantee reliable delivery, and moderately busy sites will lose log messages occasionally, especially in periods of high traffic which may be the result of an attack. In addition, remote `rsyslog` messages are not authenticated in any way by default, so it is easy for an attacker to introduce spurious messages to the central log server. Also, some problems cause loss of network connectivity, which will prevent the sending of messages to the central server. For all of these reasons, it is better to store log messages both centrally and on each host, so that they can be correlated if necessary.

contains 1 rule

#### Ensure Logs Sent To Remote Host [ref]rule

To configure rsyslog to send logs to a remote log server, open `/etc/rsyslog.conf` and read and understand the last section of the file, which describes the multiple directives necessary to activate remote logging. Along with these other directives, the system can be configured to forward its logs to a particular log server by adding or correcting one of the following lines, substituting `loghost.example.com` appropriately. The choice of protocol depends on the environment of the system; although TCP and RELP provide more reliable message delivery, they may not be supported in all environments.
To use UDP for log message delivery:

    *.* @loghost.example.com

To use TCP for log message delivery:

    *.* @@loghost.example.com

To use RELP for log message delivery:

    *.* :omrelp:loghost.example.com

Rationale:

A log server (loghost) receives syslog messages from one or more systems. This data can be used as an additional log source in the event a system is compromised and its local logs are suspect. Forwarding log messages to a remote loghost also provides system administrators with a centralized place to view the status of multiple hosts within the enterprise.

Severity: low

Identifiers: CCE-27343-3

References: AU-3(2), AU-4(1), AU-9, 366, 1348, 136, 1851, 5.1.5, SRG-OS-000480-GPOS-00227, RHEL-07-030770

### Configure rsyslogd to Accept Remote Messages If Acting as a Log Server [ref]group

By default, `rsyslog` does not listen over the network for log messages. If needed, modules can be enabled to allow the rsyslog daemon to receive messages from other systems and for the system thus to act as a log server. If the machine is not a log server, then lines concerning these modules should remain commented out.

contains 1 rule

#### Ensure rsyslog Does Not Accept Remote Messages Unless Acting As Log Server [ref]rule

The `rsyslog` daemon should not accept remote messages unless the system acts as a log server. To ensure that it is not listening on the network, ensure the following lines are not found in `/etc/rsyslog.conf`:

    $ModLoad imtcp
    $InputTCPServerRun port
    $ModLoad imudp
    $UDPServerRun port
    $ModLoad imrelp
    $InputRELPServerRun port

Rationale:

Any process which receives messages from the network incurs some risk of receiving malicious messages. This risk can be eliminated for rsyslog by configuring it not to listen on the network.

Severity: low

Identifiers: CCE-80192-8

References: AU-9(2), AC-4, CM-6(c), 318, 368, 1812, 1813, 1814, SRG-OS-000480-GPOS-00227, RHEL-07-030780

### System Accounting with auditd [ref]group

The audit service provides substantial capabilities for recording system activities. By default, the service audits about SELinux AVC denials and certain types of security-relevant events such as system logins, account modifications, and authentication events performed by programs such as sudo. Under its default configuration, `auditd` has modest disk space requirements, and should not noticeably impact system performance.
NOTE: The Linux Audit daemon `auditd` can be configured to use the `augenrules` program to read audit rules files (`*.rules`) located in `/etc/audit/rules.d` location and compile them to create the resulting form of the `/etc/audit/audit.rules` configuration file during the daemon startup (default configuration). Alternatively, the `auditd` daemon can use the `auditctl` utility to read audit rules from the `/etc/audit/audit.rules` configuration file during daemon startup, and load them into the kernel. The expected behavior is configured via the appropriate `ExecStartPost` directive setting in the `/usr/lib/systemd/system/auditd.service` configuration file. To instruct the `auditd` daemon to use the `augenrules` program to read audit rules (default configuration), use the following setting:

    ExecStartPost=-/sbin/augenrules --load

in the `/usr/lib/systemd/system/auditd.service` configuration file. In order to instruct the `auditd` daemon to use the `auditctl` utility to read audit rules, use the following setting:

    ExecStartPost=-/sbin/auditctl -R /etc/audit/audit.rules

in the `/usr/lib/systemd/system/auditd.service` configuration file. Refer to `[Service]` section of the `/usr/lib/systemd/system/auditd.service` configuration file for further details.
Government networks often have substantial auditing requirements and `auditd` can be configured to meet these requirements. Examining some example audit records demonstrates how the Linux audit system satisfies common requirements. The following example from Fedora Documentation available at `https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/SELinux_Users_and_Administrators_Guide/sect-Security-Enhanced_Linux-Troubleshooting-Fixing_Problems.html#sect-Security-Enhanced_Linux-Fixing_Problems-Raw_Audit_Messages` shows the substantial amount of information captured in a two typical "raw" audit messages, followed by a breakdown of the most important fields. In this example the message is SELinux-related and reports an AVC denial (and the associated system call) that occurred when the Apache HTTP Server attempted to access the `/var/www/html/file1` file (labeled with the `samba_share_t` type):

    type=AVC msg=audit(1226874073.147:96): avc:  denied  { getattr } for pid=2465 comm="httpd"
    path="/var/www/html/file1" dev=dm-0 ino=284133 scontext=unconfined_u:system_r:httpd_t:s0
    tcontext=unconfined_u:object_r:samba_share_t:s0 tclass=file

    type=SYSCALL msg=audit(1226874073.147:96): arch=40000003 syscall=196 success=no exit=-13
    a0=b98df198 a1=bfec85dc a2=54dff4 a3=2008171 items=0 ppid=2463 pid=2465 auid=502 uid=48
    gid=48 euid=48 suid=48 fsuid=48 egid=48 sgid=48 fsgid=48 tty=(none) ses=6 comm="httpd"
    exe="/usr/sbin/httpd" subj=unconfined_u:system_r:httpd_t:s0 key=(null)

- `msg=audit(1226874073.147:96)`
  - The number in parentheses is the unformatted time stamp (Epoch time) for the event, which can be converted to standard time by using the `date` command.
- `{ getattr }`
  - The item in braces indicates the permission that was denied. `getattr` indicates the source process was trying to read the target file's status information. This occurs before reading files. This action is denied due to the file being accessed having the wrong label. Commonly seen permissions include `getattr`, `read`, and `write`.
- `comm="httpd"`
  - The executable that launched the process. The full path of the executable is found in the `exe=` section of the system call (`SYSCALL`) message, which in this case, is `exe="/usr/sbin/httpd"`.
- `path="/var/www/html/file1"`
  - The path to the object (target) the process attempted to access.
- `scontext="unconfined_u:system_r:httpd_t:s0"`
  - The SELinux context of the process that attempted the denied action. In this case, it is the SELinux context of the Apache HTTP Server, which is running in the `httpd_t` domain.
- `tcontext="unconfined_u:object_r:samba_share_t:s0"`
  - The SELinux context of the object (target) the process attempted to access. In this case, it is the SELinux context of `file1`. Note: the `samba_share_t` type is not accessible to processes running in the `httpd_t` domain.
- From the system call (`SYSCALL`) message, two items are of interest:
  - `success=no`: indicates whether the denial (AVC) was enforced or not. `success=no` indicates the system call was not successful (SELinux denied access). `success=yes` indicates the system call was successful - this can be seen for permissive domains or unconfined domains, such as `initrc_t` and `kernel_t`.
  - `exe="/usr/sbin/httpd"`: the full path to the executable that launched the process, which in this case, is `exe="/usr/sbin/httpd"`.

contains 41 rules

### Configure auditd Data Retention [ref]group

The audit system writes data to `/var/log/audit/audit.log`. By default, `auditd` rotates 5 logs by size (6MB), retaining a maximum of 30MB of data in total, and refuses to write entries when the disk is too full. This minimizes the risk of audit data filling its partition and impacting other services. This also minimizes the risk of the audit daemon temporarily disabling the system if it cannot write audit log (which it can be configured to do). For a busy system or a system which is thoroughly auditing system activity, the default settings for data retention may be insufficient. The log file size needed will depend heavily on what types of events are being audited. First configure auditing to log all the events of interest. Then monitor the log size manually for awhile to determine what file size will allow you to keep the required data for the correct time period.
Using a dedicated partition for `/var/log/audit` prevents the `auditd` logs from disrupting system functionality if they fill, and, more importantly, prevents other activity in `/var` from filling the partition and stopping the audit trail. (The audit logs are size-limited and therefore unlikely to grow without bound unless configured to do so.) Some machines may have requirements that no actions occur which cannot be audited. If this is the case, then `auditd` can be configured to halt the machine if it runs out of space. Note: Since older logs are rotated, configuring `auditd` this way does not prevent older logs from being rotated away before they can be viewed. If your system is configured to halt when logging cannot be performed, make sure this can never happen under normal circumstances! Ensure that `/var/log/audit` is on its own partition, and that this partition is larger than the maximum amount of data `auditd` will retain normally.

References: AU-11, 138

contains 8 rules

#### Configure auditd Number of Logs Retained [ref]rule

Determine how many log files `auditd` should retain when it rotates logs. Edit the file `/etc/audit/auditd.conf`. Add or modify the following line, substituting NUMLOGS with the correct value of 5:

    num_logs = NUMLOGS

Set the value to 5 for general-purpose systems. Note that values less than 2 result in no log rotation.Rationale:

The total storage for audit log files must be large enough to retain log information over the period required. This is a function of the maximum log file size and the number of logs retained.

Severity: medium

Identifiers: CCE-27348-2

References: AU-1(b), AU-11, IR-5, Req-10.7

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_auditd_num_logs="5"

    AUDITCONFIG=/etc/audit/auditd.conf

    grep -q ^num_logs $AUDITCONFIG && \
      sed -i 's/^num_logs.*/num_logs = '"$var_auditd_num_logs"'/g' $AUDITCONFIG
    if ! [ $? -eq 0 ]; then
      echo "num_logs = $var_auditd_num_logs" >> $AUDITCONFIG
    fi

#### Configure auditd Max Log File Size [ref]rule

Determine the amount of audit data (in megabytes) which should be retained in each log file. Edit the file `/etc/audit/auditd.conf`. Add or modify the following line, substituting the correct value of 6 for STOREMB:

    max_log_file = STOREMB

Set the value to `6` (MB) or higher for general-purpose systems. Larger values, of course, support retention of even more audit data.Rationale:

The total storage for audit log files must be large enough to retain log information over the period required. This is a function of the maximum log file size and the number of logs retained.

Severity: medium

Identifiers: CCE-27319-3

References: AU-1(b), AU-11, IR-5, Req-10.7, 5.2.1.1

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_auditd_max_log_file="6"

    AUDITCONFIG=/etc/audit/auditd.conf

    grep -q ^max_log_file $AUDITCONFIG && \
      sed -i 's/^max_log_file.*/max_log_file = '"$var_auditd_max_log_file"'/g' $AUDITCONFIG
    if ! [ $? -eq 0 ]; then
      echo "max_log_file = $var_auditd_max_log_file" >> $AUDITCONFIG
    fi

#### Configure auditd max_log_file_action Upon Reaching Maximum Log Size [ref]rule

The default action to take when the logs reach their maximum size is to rotate the log files, discarding the oldest one. To configure the action taken by `auditd`, add or correct the line in `/etc/audit/auditd.conf`:

    max_log_file_action = ACTION

Possible values for ACTION are described in the `auditd.conf` man page. These include:

- `ignore`
- `syslog`
- `suspend`
- `rotate`
- `keep_logs`

Set the `ACTION` to `rotate` to ensure log rotation occurs. This is the default. The setting is case-insensitive. Rationale:

Automatically rotating logs (by setting this to `rotate`) minimizes the chances of the system unexpectedly running out of disk space by being overwhelmed with log data. However, for systems that must never discard log data, or which use external processes to transfer it and reclaim space, `keep_logs` can be employed.

Severity: medium

Identifiers: CCE-27231-0

References: AU-1(b), AU-4, AU-11, IR-5, Req-10.7, 5.2.1.3

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_auditd_max_log_file_action="rotate"

    AUDITCONFIG=/etc/audit/auditd.conf

    grep -q ^max_log_file_action $AUDITCONFIG && \
      sed -i 's/^max_log_file_action.*/max_log_file_action = '"$var_auditd_max_log_file_action"'/g' $AUDITCONFIG
    if ! [ $? -eq 0 ]; then
      echo "max_log_file_action = $var_auditd_max_log_file_action" >> $AUDITCONFIG
    fi

#### Configure auditd space_left Action on Low Disk Space [ref]rule

The `auditd` service can be configured to take an action when disk space starts to run low. Edit the file `/etc/audit/auditd.conf`. Modify the following line, substituting ACTION appropriately:

    space_left_action = ACTION

Possible values for ACTION are described in the `auditd.conf` man page. These include:

- `ignore`
- `syslog`
- `email`
- `exec`
- `suspend`
- `single`
- `halt`

Set this to `email` (instead of the default, which is `suspend`) as it is more likely to get prompt attention. Acceptable values also include `suspend`, `single`, and `halt`. Rationale:

Notifying administrators of an impending disk space problem may allow them to take corrective action prior to any disruption.

Severity: medium

Identifiers: CCE-27375-5

References: AU-1(b), AU-4, AU-5(1), AU-5(b), IR-5, 1855, Req-10.7, 5.2.1.2, SRG-OS-000343-GPOS-00134, RHEL-07-030351

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_auditd_space_left_action="email"

    grep -q ^space_left_action /etc/audit/auditd.conf && \
      sed -i "s/space_left_action.*/space_left_action = $var_auditd_space_left_action/g" /etc/audit/auditd.conf
    if ! [ $? -eq 0 ]; then
        echo "space_left_action = $var_auditd_space_left_action" >> /etc/audit/auditd.conf
    fi

#### Configure auditd admin_space_left Action on Low Disk Space [ref]rule

The `auditd` service can be configured to take an action when disk space is running low but prior to running out of space completely. Edit the file `/etc/audit/auditd.conf`. Add or modify the following line, substituting ACTION appropriately:

    admin_space_left_action = ACTION

Set this value to `single` to cause the system to switch to single user mode for corrective action. Acceptable values also include `suspend` and `halt`. For certain systems, the need for availability outweighs the need to log all actions, and a different setting should be determined. Details regarding all possible values for ACTION are described in the `auditd.conf` man page. Rationale:

Administrators should be made aware of an inability to record audit records. If a separate partition or logical volume of adequate size is used, running low on space for audit records should never occur.

Severity: medium

Identifiers: CCE-27370-6

References: AU-1(b), AU-4, AU-5(b), IR-5, 140, 1343, Req-10.7, 5.2.1.2

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_auditd_admin_space_left_action="single"

    grep -q ^admin_space_left_action /etc/audit/auditd.conf && \
      sed -i "s/admin_space_left_action.*/admin_space_left_action = $var_auditd_admin_space_left_action/g" /etc/audit/auditd.conf
    if ! [ $? -eq 0 ]; then
        echo "admin_space_left_action = $var_auditd_admin_space_left_action" >> /etc/audit/auditd.conf
    fi

#### Configure auditd mail_acct Action on Low Disk Space [ref]rule

The `auditd` service can be configured to send email to a designated account in certain situations. Add or correct the following line in `/etc/audit/auditd.conf` to ensure that administrators are notified via email for those situations:

    action_mail_acct = root

Rationale:

Email sent to the root account is typically aliased to the administrators of the system, who can take appropriate action.

Severity: medium

Identifiers: CCE-27394-6

References: AU-1(b), AU-4, AU-5(1), AU-5(a), IR-5, 1855, Req-10.7.a, 5.2.1.2, SRG-OS-000343-GPOS-00134, RHEL-07-030352

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_auditd_action_mail_acct="root"

    AUDITCONFIG=/etc/audit/auditd.conf

    grep -q ^action_mail_acct $AUDITCONFIG && \
      sed -i 's/^action_mail_acct.*/action_mail_acct = '"$var_auditd_action_mail_acct"'/g' $AUDITCONFIG
    if ! [ $? -eq 0 ]; then
      echo "action_mail_acct = $var_auditd_action_mail_acct" >> $AUDITCONFIG
    fi

#### Configure auditd flush priority [ref]rule

The `auditd` service can be configured to synchronously write audit event data to disk. Add or correct the following line in `/etc/audit/auditd.conf` to ensure that audit event data is fully synchronized with the log files on the disk:

    flush = data

Rationale:

Audit data should be synchronously written to disk to ensure log integrity. These parameters assure that all audit event data is fully synchronized with the log files on the disk.

Severity: low

Identifiers: CCE-27331-8

References: AU-9, AU-12(1), 1576

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_auditd_flush="data"

    AUDITCONFIG=/etc/audit/auditd.conf

    # if flush is present, flush param edited to var_auditd_flush
    # else flush param is defined by var_auditd_flush
    #
    # the freq param is only used value 'incremental' and will be
    # commented out if flush != incremental
    #
    # if flush == incremental && freq param is not defined, it
    # will be defined as the package-default value of 20

    grep -q ^flush $AUDITCONFIG && \
      sed -i 's/^flush.*/flush = '"$var_auditd_flush"'/g' $AUDITCONFIG
    if ! [ $? -eq 0 ]; then
      echo "flush = $var_auditd_flush" >> $AUDITCONFIG
    fi

    if ! [ "$var_auditd_flush" == "incremental" ]; then
      sed -i 's/^freq/##freq/g' $AUDITCONFIG
    elif [ "$var_auditd_flush" == "incremental" ]; then
      grep -q freq $AUDITCONFIG && \
        sed -i 's/^#\+freq/freq/g' $AUDITCONFIG
      if ! [ $? -eq 0 ]; then
        echo "freq = 20" >> $AUDITCONFIG
      fi
    fi

#### Configure auditd to use audispd's syslog plugin [ref]rule

To configure the `auditd` service to use the `syslog` plug-in of the `audispd` audit event multiplexor, set the `active` line in `/etc/audisp/plugins.d/syslog.conf` to `yes`. Restart the `auditd` service:

    $ sudo service auditd restart

Rationale:

The auditd service does not include the ability to send audit records to a centralized server for management directly. It does, however, include a plug-in for audit event multiplexor (audispd) to pass audit records to the local syslog server

Severity: medium

Identifiers: CCE-27341-7

References: AU-1(b), AU-3(2), IR-5, 136, Req-10.5.3

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    grep -q ^active /etc/audisp/plugins.d/syslog.conf && \
      sed -i "s/active.*/active = yes/g" /etc/audisp/plugins.d/syslog.conf
    if ! [ $? -eq 0 ]; then
        echo "active = yes" >> /etc/audisp/plugins.d/syslog.conf
    fi

### Configure auditd Rules for Comprehensive Auditing [ref]group

The `auditd` program can perform comprehensive monitoring of system activity. This section describes recommended configuration settings for comprehensive auditing, but a full description of the auditing system's capabilities is beyond the scope of this guide. The mailing list linux-audit@redhat.com exists to facilitate community discussion of the auditing system.
The audit subsystem supports extensive collection of events, including:

- Tracing of arbitrary system calls (identified by name or number) on entry or exit.
- Filtering by PID, UID, call success, system call argument (with some limitations), etc.
- Monitoring of specific files for modifications to the file's contents or metadata.

Auditing rules at startup are controlled by the file `/etc/audit/audit.rules`. Add rules to it to meet the auditing requirements for your organization. Each line in `/etc/audit/audit.rules` represents a series of arguments that can be passed to `auditctl` and can be individually tested during runtime. See documentation in `/usr/share/doc/audit-VERSION` and in the related man pages for more details.
If copying any example audit rulesets from `/usr/share/doc/audit-VERSION`, be sure to comment out the lines containing `arch=` which are not appropriate for your system's architecture. Then review and understand the following rules, ensuring rules are activated as needed for the appropriate architecture.
After reviewing all the rules, reading the following sections, and editing as needed, the new rules can be activated as follows:

    $ sudo service auditd restart

contains 31 rules

### Records Events that Modify Date and Time Information [ref]group

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time. All changes to the system time should be audited.

contains 5 rules

#### Record attempts to alter time through adjtimex [ref]rule

If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S adjtimex -k audit_time_rules

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S adjtimex -k audit_time_rules

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S adjtimex -k audit_time_rules

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S adjtimex -k audit_time_rules

The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls:

    -a always,exit -F arch=b64 -S adjtimex -S settimeofday -k audit_time_rules

Rationale:

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.

Severity: low

Identifiers: CCE-27290-6

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 5.2.4, Req-10.4.2.b, 1487, 169

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    function rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation {

    # Perform the remediation for the 'adjtimex', 'settimeofday', and 'stime' audit
    # system calls on Red Hat Enterprise Linux 7 or Fedora OSes
    #
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do

            PATTERN="-a always,exit -F arch=${ARCH} -S .* -k *"
            # Create expected audit group and audit rule form for particular system call & architecture
            if [ ${ARCH} = "b32" ]
            then
                    # stime system call is known at 32-bit arch (see e.g "$ ausyscall i386 stime" 's output)
                    # so append it to the list of time group system calls to be audited
                    GROUP="\(adjtimex\|settimeofday\|stime\)"
                    FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -S stime -k audit_time_rules"
            elif [ ${ARCH} = "b64" ]
            then
                    # stime system call isn't known at 64-bit arch (see "$ ausyscall x86_64 stime" 's output)
                    # therefore don't add it to the list of time group system calls to be audited
                    GROUP="\(adjtimex\|settimeofday\)"
                    FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -k audit_time_rules"
            fi
            # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'
            fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
            fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

    }

    rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation

#### Record attempts to alter time through settimeofday [ref]rule

If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S settimeofday -k audit_time_rules

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S settimeofday -k audit_time_rules

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S settimeofday -k audit_time_rules

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S settimeofday -k audit_time_rules

The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls:

    -a always,exit -F arch=b64 -S adjtimex -S settimeofday -k audit_time_rules

Rationale:

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.

Severity: low

Identifiers: CCE-27216-1

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 5.2.4, Req-10.4.2.b, 1487, 169

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    function rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation {

    # Perform the remediation for the 'adjtimex', 'settimeofday', and 'stime' audit
    # system calls on Red Hat Enterprise Linux 7 or Fedora OSes
    #
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do

            PATTERN="-a always,exit -F arch=${ARCH} -S .* -k *"
            # Create expected audit group and audit rule form for particular system call & architecture
            if [ ${ARCH} = "b32" ]
            then
                    # stime system call is known at 32-bit arch (see e.g "$ ausyscall i386 stime" 's output)
                    # so append it to the list of time group system calls to be audited
                    GROUP="\(adjtimex\|settimeofday\|stime\)"
                    FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -S stime -k audit_time_rules"
            elif [ ${ARCH} = "b64" ]
            then
                    # stime system call isn't known at 64-bit arch (see "$ ausyscall x86_64 stime" 's output)
                    # therefore don't add it to the list of time group system calls to be audited
                    GROUP="\(adjtimex\|settimeofday\)"
                    FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -k audit_time_rules"
            fi
            # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'
            fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
            fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

    }

    rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation

#### Record Attempts to Alter Time Through stime [ref]rule

If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d` for both 32 bit and 64 bit systems:

    -a always,exit -F arch=b32 -S stime -k audit_time_rules

Since the 64 bit version of the "stime" system call is not defined in the audit lookup table, the corresponding "-F arch=b64" form of this rule is not expected to be defined on 64 bit systems (the aforementioned "-F arch=b32" stime rule form itself is sufficient for both 32 bit and 64 bit systems). If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file for both 32 bit and 64 bit systems:

    -a always,exit -F arch=b32 -S stime -k audit_time_rules

Since the 64 bit version of the "stime" system call is not defined in the audit lookup table, the corresponding "-F arch=b64" form of this rule is not expected to be defined on 64 bit systems (the aforementioned "-F arch=b32" stime rule form itself is sufficient for both 32 bit and 64 bit systems). The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined system calls:

    -a always,exit -F arch=b64 -S adjtimex -S settimeofday -k audit_time_rules

Rationale:

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.

Severity: low

Identifiers: CCE-27299-7

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, Req-10.4.2.b, 1487, 169

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    function rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation {

    # Perform the remediation for the 'adjtimex', 'settimeofday', and 'stime' audit
    # system calls on Red Hat Enterprise Linux 7 or Fedora OSes
    #
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do

            PATTERN="-a always,exit -F arch=${ARCH} -S .* -k *"
            # Create expected audit group and audit rule form for particular system call & architecture
            if [ ${ARCH} = "b32" ]
            then
                    # stime system call is known at 32-bit arch (see e.g "$ ausyscall i386 stime" 's output)
                    # so append it to the list of time group system calls to be audited
                    GROUP="\(adjtimex\|settimeofday\|stime\)"
                    FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -S stime -k audit_time_rules"
            elif [ ${ARCH} = "b64" ]
            then
                    # stime system call isn't known at 64-bit arch (see "$ ausyscall x86_64 stime" 's output)
                    # therefore don't add it to the list of time group system calls to be audited
                    GROUP="\(adjtimex\|settimeofday\)"
                    FULL_RULE="-a always,exit -F arch=${ARCH} -S adjtimex -S settimeofday -k audit_time_rules"
            fi
            # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'
            fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
            fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

    }

    rhel7_fedora_perform_audit_adjtimex_settimeofday_stime_remediation

#### Record Attempts to Alter Time Through clock_settime [ref]rule

If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S clock_settime -F a0=0x0 -F key=time-change

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S clock_settime -F a0=0x0 -F key=time-change

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S clock_settime -F a0=0x0 -F key=time-change

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S clock_settime -F a0=0x0 -F key=time-change

The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport. Multiple system calls can be defined on the same line to save space if desired, but is not required. See an example of multiple combined syscalls:

    -a always,exit -F arch=b64 -S adjtimex -S settimeofday -k audit_time_rules

Rationale:

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.

Severity: low

Identifiers: CCE-27219-5

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 5.2.4, Req-10.4.2.b, 1487, 169

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # First perform the remediation of the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ "$(getconf LONG_BIT)" = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=$ARCH -S clock_settime -F a0=.* \(-F key=\|-k \).*"
    	GROUP="clock_settime"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S clock_settime -F a0=0x0 -k time-change"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Attempts to Alter the localtime File [ref]rule

If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -w /etc/localtime -p wa -k audit_time_rules

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -w /etc/localtime -p wa -k audit_time_rules

The -k option allows for the specification of a key in string form that can be used for better reporting capability through ausearch and aureport and should always be used. Rationale:

Arbitrary changes to the system time can be used to obfuscate nefarious activities in log files, as well as to confuse network services that are highly dependent upon an accurate system time (such as sshd). All changes to the system time should be audited.

Severity: low

Identifiers: CCE-27310-2

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(b), IR-5, 5.2.4, Req-10.4.2.b, 1487, 169

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/localtime" "wa" "audit_time_rules"
    fix_audit_watch_rule "augenrules" "/etc/localtime" "wa" "audit_time_rules"

### Record Events that Modify the System's Discretionary Access Controls [ref]group

At a minimum the audit system should collect file permission changes for all users and root. Note that the "-F arch=b32" lines should be present even on a 64 bit system. These commands identify system calls for auditing. Even if the system is 64 bit it can still execute 32 bit system calls. Additionally, these rules can be configured in a number of ways while still achieving the desired effect. An example of this is that the "-S" calls could be split up and placed on separate lines, however, this is less efficient. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod
        -a always,exit -F arch=b32 -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod
        -a always,exit -F arch=b32 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If your system is 64 bit then these lines should be duplicated and the arch=b32 replaced with arch=b64 as follows:

    -a always,exit -F arch=b64 -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod
        -a always,exit -F arch=b64 -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod
        -a always,exit -F arch=b64 -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

contains 13 rules

#### Record Events that Modify the System's Discretionary Access Controls - chmod [ref]rule

At a minimum the audit system should collect file permission changes for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S chmod -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S chmod  -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S chmod -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S chmod  -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: low

Identifiers: CCE-27339-1

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, RHEL-07-030390

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=$ARCH -S .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="chmod"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - chown [ref]rule

At a minimum the audit system should collect file permission changes for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S chown -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S chown -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S chown -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S chown -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: low

Identifiers: CCE-27364-9

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, SRG-OS-000474-GPOS-00219, RHEL-07-030380

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=${ARCH} -S .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="chown"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - fchmod [ref]rule

At a minimum the audit system should collect file permission changes for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S fchmod -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fchmod -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S fchmod -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fchmod -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: low

Identifiers: CCE-27393-8

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, RHEL-07-030391

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=$ARCH -S .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="chmod"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - fchmodat [ref]rule

At a minimum the audit system should collect file permission changes for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: low

Identifiers: CCE-27388-8

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, RHEL-07-030392

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=$ARCH -S .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="chmod"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S chmod -S fchmod -S fchmodat -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - fchown [ref]rule

At a minimum the audit system should collect file permission changes for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S fchown -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fchown -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S fchown -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fchown -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: low

Identifiers: CCE-27356-5

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, SRG-OS-000474-GPOS-00219, RHEL-07-030381

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=${ARCH} -S .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="chown"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - fchownat [ref]rule

At a minimum the audit system should collect file permission changes for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S fchownat -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fchownat -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S fchownat -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fchownat -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: low

Identifiers: CCE-27387-0

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, SRG-OS-000474-GPOS-00219, RHEL-07-030383

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=${ARCH} -S .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="chown"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - fremovexattr [ref]rule

At a minimum the audit system should collect file permission changes for all users and root.
If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: medium

Identifiers: CCE-27353-2

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, RHEL-07-030404

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - fsetxattr [ref]rule

At a minimum the audit system should collect file permission changes for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S fsetxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fsetxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S fsetxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S fsetxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: low

Identifiers: CCE-27389-6

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, RHEL-07-030401

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - lchown [ref]rule

At a minimum the audit system should collect file permission changes for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: low

Identifiers: CCE-27083-5

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, SRG-OS-000474-GPOS-00219, RHEL-07-030382

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=${ARCH} -S .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="chown"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S chown -S fchown -S fchownat -S lchown -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - lremovexattr [ref]rule

At a minimum the audit system should collect file permission changes for all users and root.
If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S lremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S lremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S lremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S lremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: medium

Identifiers: CCE-27410-0

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, RHEL-07-030405

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - lsetxattr [ref]rule

At a minimum the audit system should collect file permission changes for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S lsetxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S lsetxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S lsetxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S lsetxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: low

Identifiers: CCE-27280-7

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, SRG-OS-000474-GPOS-00219, RHEL-07-030402

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - removexattr [ref]rule

At a minimum the audit system should collect file permission changes for all users and root.
If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S removexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S removexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S removexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S removexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: medium

Identifiers: CCE-27367-2

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, RHEL-07-030403

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify the System's Discretionary Access Controls - setxattr [ref]rule

At a minimum the audit system should collect file permission changes for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S setxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S setxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S setxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following line:

    -a always,exit -F arch=b64 -S setxattr -F auid>=1000 -F auid!=4294967295 -k perm_mod

Warning: Note that these rules can be configured in a number of ways while still achieving the desired effect. Here the system calls have been placed independent of other system calls. Grouping these system calls with others as identifying earlier in this guide is more efficient.
Rationale:

The changing of file permissions could indicate that a user is attempting to gain access to information that would otherwise be disallowed. Auditing DAC modifications can facilitate the identification of patterns of abuse among both authorized and unauthorized users.

Severity: low

Identifiers: CCE-27213-8

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126, 172, Req-10.5.5, 5.2.10, SRG-OS-000064-GPOS-00033, SRG-OS-000392-GPOS-00172, SRG-OS-000458-GPOS-00203, RHEL-07-030400

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=1000 -F auid!=4294967295 -k perm_mod"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Record Events that Modify User/Group Information [ref]rule

If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following lines to a file with suffix `.rules` in the directory `/etc/audit/rules.d`, in order to capture events that modify account changes:

    -w /etc/group -p wa -k audit_rules_usergroup_modification
    -w /etc/passwd -p wa -k audit_rules_usergroup_modification
    -w /etc/gshadow -p wa -k audit_rules_usergroup_modification
    -w /etc/shadow -p wa -k audit_rules_usergroup_modification
    -w /etc/security/opasswd -p wa -k audit_rules_usergroup_modification

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following lines to `/etc/audit/audit.rules` file, in order to capture events that modify account changes:

    -w /etc/group -p wa -k audit_rules_usergroup_modification
    -w /etc/passwd -p wa -k audit_rules_usergroup_modification
    -w /etc/gshadow -p wa -k audit_rules_usergroup_modification
    -w /etc/shadow -p wa -k audit_rules_usergroup_modification
    -w /etc/security/opasswd -p wa -k audit_rules_usergroup_modification

Rationale:

In addition to auditing new user and group accounts, these watches will alert the system administrator(s) to any modifications. Any unexpected users, groups, or modifications should be investigated for legitimacy.

Severity: low

Identifiers: CCE-27192-4

References: AC-2(4), AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 18, 172, 1403, 2130, RHEL-07-030710, Req-10.2.5, 5.2.5, SRG–OS–000004–GPOS–00004, SRG–OS–000239–GPOS–00089, SRG–OS–000241–GPOS–00090, SRG–OS–000241–GPOS–00091, SRG–OS–000303–GPOS–00120, SRG–OS–000476–GPOS–00221

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation
    # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/group" "wa" "audit_rules_usergroup_modification"
    fix_audit_watch_rule "augenrules" "/etc/group" "wa" "audit_rules_usergroup_modification"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/passwd" "wa" "audit_rules_usergroup_modification"
    fix_audit_watch_rule "augenrules" "/etc/passwd" "wa" "audit_rules_usergroup_modification"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/gshadow" "wa" "audit_rules_usergroup_modification"
    fix_audit_watch_rule "augenrules" "/etc/gshadow" "wa" "audit_rules_usergroup_modification"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/shadow" "wa" "audit_rules_usergroup_modification"
    fix_audit_watch_rule "augenrules" "/etc/shadow" "wa" "audit_rules_usergroup_modification"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/security/opasswd" "wa" "audit_rules_usergroup_modification"
    fix_audit_watch_rule "augenrules" "/etc/security/opasswd" "wa" "audit_rules_usergroup_modification"

#### Record Events that Modify the System's Network Environment [ref]rule

If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following lines to a file with suffix `.rules` in the directory `/etc/audit/rules.d`, setting ARCH to either b32 or b64 as appropriate for your system:

    -a always,exit -F arch=ARCH -S sethostname -S setdomainname -k audit_rules_networkconfig_modification
    -w /etc/issue -p wa -k audit_rules_networkconfig_modification
    -w /etc/issue.net -p wa -k audit_rules_networkconfig_modification
    -w /etc/hosts -p wa -k audit_rules_networkconfig_modification
    -w /etc/sysconfig/network -p wa -k audit_rules_networkconfig_modification

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following lines to `/etc/audit/audit.rules` file, setting ARCH to either b32 or b64 as appropriate for your system:

    -a always,exit -F arch=ARCH -S sethostname -S setdomainname -k audit_rules_networkconfig_modification
    -w /etc/issue -p wa -k audit_rules_networkconfig_modification
    -w /etc/issue.net -p wa -k audit_rules_networkconfig_modification
    -w /etc/hosts -p wa -k audit_rules_networkconfig_modification
    -w /etc/sysconfig/network -p wa -k audit_rules_networkconfig_modification

Rationale:

The network environment should not be modified by anything other than administrator action. Any change to network parameters should be audited.

Severity: low

Identifiers: CCE-27076-9

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, Req-10.5.5, 5.2.6

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # First perform the remediation of the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=$ARCH -S .* -k *"
    	# Use escaped BRE regex to specify rule group
    	GROUP="set\(host\|domain\)name"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S sethostname -S setdomainname -k audit_rules_networkconfig_modification"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

    # Then perform the remediations for the watch rules
    # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/issue" "wa" "audit_rules_networkconfig_modification"
    fix_audit_watch_rule "augenrules" "/etc/issue" "wa" "audit_rules_networkconfig_modification"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/issue.net" "wa" "audit_rules_networkconfig_modification"
    fix_audit_watch_rule "augenrules" "/etc/issue.net" "wa" "audit_rules_networkconfig_modification"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/hosts" "wa" "audit_rules_networkconfig_modification"
    fix_audit_watch_rule "augenrules" "/etc/hosts" "wa" "audit_rules_networkconfig_modification"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/sysconfig/network" "wa" "audit_rules_networkconfig_modification"
    fix_audit_watch_rule "augenrules" "/etc/sysconfig/network" "wa" "audit_rules_networkconfig_modification"

#### System Audit Logs Must Have Mode 0640 or Less Permissive [ref]rule

If `log_group` in `/etc/audit/auditd.conf` is set to a group other than the `root` group account, change the mode of the audit log files with the following command:

    $ sudo chmod 0640 audit_file

Otherwise, change the mode of the audit log files with the following command:

    $ sudo chmod 0600 audit_file

Rationale:

If users can write to audit logs, audit trails can be modified or destroyed.

Severity: medium

Identifiers: CCE-27205-4

References: AC-6, AU-1(b), AU-9, IR-5, http://iase.disa.mil/stigs/cci/Pages/index.aspx, Req-10.5

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    if `grep -q ^log_group /etc/audit/auditd.conf` ; then
      GROUP=$(awk -F "=" '/log_group/ {print $2}' /etc/audit/auditd.conf | tr -d ' ')
      if ! [ "${GROUP}" == 'root' ] ; then
        chmod 0640 /var/log/audit/audit.log
        chmod 0440 /var/log/audit/audit.log.*
      else
        chmod 0600 /var/log/audit/audit.log
        chmod 0400 /var/log/audit/audit.log.*
      fi

      chmod 0640 /etc/audit/audit*
      chmod 0640 /etc/audit/rules.d/*
    else
      chmod 0600 /var/log/audit/audit.log
      chmod 0400 /var/log/audit/audit.log.*
      chmod 0640 /etc/audit/audit*
      chmod 0640 /etc/audit/rules.d/*
    fi

#### Record Events that Modify the System's Mandatory Access Controls [ref]rule

If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -w /etc/selinux/ -p wa -k MAC-policy

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -w /etc/selinux/ -p wa -k MAC-policy

Rationale:

The system's mandatory access policy (SELinux) should not be arbitrarily changed by anything other than administrator action. All changes to MAC policy should be audited.

Severity: low

Identifiers: CCE-27168-4

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, Req-10.5.5, 5.2.7

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/selinux/" "wa" "MAC-policy"
    fix_audit_watch_rule "augenrules" "/etc/selinux/" "wa" "MAC-policy"

#### Record Attempts to Alter Logon and Logout Events [ref]rule

The audit system already collects login information for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following lines to a file with suffix `.rules` in the directory `/etc/audit/rules.d` in order to watch for attempted manual edits of files involved in storing logon events:

    -w /var/log/tallylog -p wa -k logins
    -w /var/run/faillock/ -p wa -k logins
    -w /var/log/lastlog -p wa -k logins

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following lines to `/etc/audit/audit.rules` file in order to watch for unattempted manual edits of files involved in storing logon events:

    -w /var/log/tallylog -p wa -k logins
    -w /var/run/faillock/ -p wa -k logins
    -w /var/log/lastlog -p wa -k logins

Rationale:

Manual editing of these files may indicate nefarious activity, such as an attacker attempting to remove evidence of an intrusion.

Severity: medium

Identifiers: CCE-27204-7

References: AC-17(7), AU-1(b), AU-12(a), AU-12(c), IR-5, 172, 2884, SRG-OS-000392-GPOS-00172, SRG-OS-000470-GPOS-00214, SRG-OS-000473-GPOS-00218, RHEL-07-030490, Req-10.2.3, 5.2.8

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/var/log/tallylog" "wa" "logins"
    fix_audit_watch_rule "augenrules" "/var/log/tallylog" "wa" "logins"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/var/run/faillock/" "wa" "logins"
    fix_audit_watch_rule "augenrules" "/var/run/faillock/" "wa" "logins"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/var/log/lastlog" "wa" "logins"
    fix_audit_watch_rule "augenrules" "/var/log/lastlog" "wa" "logins"

#### Record Attempts to Alter Process and Session Initiation Information [ref]rule

The audit system already collects process information for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following lines to a file with suffix `.rules` in the directory `/etc/audit/rules.d` in order to watch for attempted manual edits of files involved in storing such process information:

    -w /var/run/utmp -p wa -k session
    -w /var/log/btmp -p wa -k session
    -w /var/log/wtmp -p wa -k session

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following lines to `/etc/audit/audit.rules` file in order to watch for attempted manual edits of files involved in storing such process information:

    -w /var/run/utmp -p wa -k session
    -w /var/log/btmp -p wa -k session
    -w /var/log/wtmp -p wa -k session

Rationale:

Manual editing of these files may indicate nefarious activity, such as an attacker attempting to remove evidence of an intrusion.

Severity: low

Identifiers: CCE-27301-1

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, Req-10.2.3, 5.2.9

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation
    # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/var/run/utmp" "wa" "session"
    fix_audit_watch_rule "augenrules" "/var/run/utmp" "wa" "session"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/var/log/btmp" "wa" "session"
    fix_audit_watch_rule "augenrules" "/var/log/btmp" "wa" "session"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/var/log/wtmp" "wa" "session"
    fix_audit_watch_rule "augenrules" "/var/log/wtmp" "wa" "session"

#### Ensure auditd Collects Unauthorized Access Attempts to Files (unsuccessful) [ref]rule

At a minimum the audit system should collect unauthorized file accesses for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following lines to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -a always,exit -F arch=b32 -S creat -S open -S openat -S open_by_handle_at -S truncate -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=4294967295 -k access
    -a always,exit -F arch=b32 -S creat -S open -S openat -S open_by_handle_at -S truncate -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=4294967295 -k access

If the system is 64 bit then also add the following lines:

    -a always,exit -F arch=b64 -S creat -S open -S openat -S open_by_handle_at -S truncate -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=4294967295 -k access
    -a always,exit -F arch=b64 -S creat -S open -S openat -S open_by_handle_at -S truncate -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=4294967295 -k access

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following lines to `/etc/audit/audit.rules` file:

    -a always,exit -F arch=b32 -S creat -S open -S openat -S open_by_handle_at -S truncate -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=4294967295 -k access
    -a always,exit -F arch=b32 -S creat -S open -S openat -S open_by_handle_at -S truncate -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=4294967295 -k access

If the system is 64 bit then also add the following lines:

    -a always,exit -F arch=b64 -S creat -S open -S openat -S open_by_handle_at -S truncate -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=4294967295 -k access
    -a always,exit -F arch=b64 -S creat -S open -S openat -S open_by_handle_at -S truncate -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=4294967295 -k access

Rationale:

Unsuccessful attempts to access files could be an indicator of malicious activity on a system. Auditing these events could serve as evidence of potential system compromise.

Severity: medium

Identifiers: CCE-27347-4

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 172, 2884, SRG-OS-000064-GPOS-00033, SRG-OS-000458-GPOS-00203, SRG-OS-000461-GPOS-00205, SRG-OS-000392-GPOS-00172, RHEL-07-030420, Req-10.2.4, Req-10.2.1, 5.2.10

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation of the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do

    	# First fix the -EACCES requirement
    	PATTERN="-a always,exit -F arch=$ARCH -S .* -F exit=-EACCES -F auid>=1000 -F auid!=4294967295 -k *"
    	# Use escaped BRE regex to specify rule group
    	GROUP="\(creat\|open\|truncate\)"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S creat -S open -S openat -S open_by_handle_at -S truncate -S ftruncate -F exit=-EACCES -F auid>=1000 -F auid!=4294967295 -k access"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"

    	# Then fix the -EPERM requirement
    	PATTERN="-a always,exit -F arch=$ARCH -S .* -F exit=-EPERM -F auid>=1000 -F auid!=4294967295 -k *"
    	# No need to change content of $GROUP variable - it's the same as for -EACCES case above
    	FULL_RULE="-a always,exit -F arch=$ARCH -S creat -S open -S openat -S open_by_handle_at -S truncate -S ftruncate -F exit=-EPERM -F auid>=1000 -F auid!=4294967295 -k access"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"

    done

#### Ensure auditd Collects Information on the Use of Privileged Commands [ref]rule

At a minimum the audit system should collect the execution of privileged commands for all users and root. To find the relevant setuid / setgid programs, run the following command for each local partition PART:

    $ sudo find PART -xdev -type f -perm -4000 -o -type f -perm -2000 2>/dev/null

If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add a line of the following form to a file with suffix `.rules` in the directory `/etc/audit/rules.d` for each setuid / setgid program on the system, replacing the SETUID_PROG_PATH part with the full path of that setuid / setgid program in the list:

    -a always,exit -F path=SETUID_PROG_PATH -F perm=x -F auid>=1000 -F auid!=4294967295 -k privileged

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add a line of the following form to `/etc/audit/audit.rules` for each setuid / setgid program on the system, replacing the SETUID_PROG_PATH part with the full path of that setuid / setgid program in the list:

    -a always,exit -F path=SETUID_PROG_PATH -F perm=x -F auid>=1000 -F auid!=4294967295 -k privileged

Rationale:

Misuse of privileged functions, either intentionally or unintentionally by authorized users, or by unauthorized external entities that have compromised system accounts, is a serious and ongoing concern and can have significant adverse impacts on organizations. Auditing the use of privileged functions is one way to detect such misuse and identify the risk from insider and advanced persistent threast.
Privileged programs are subject to escalation-of-privilege attacks, which attempt to subvert their normal role of providing some necessary but limited capability. As such, motivation exists to monitor these programs for unusual activity.

Severity: medium

Identifiers: CCE-27437-3

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-2(4), AU-6(9), AU-12(a), AU-12(c), IR-5, 2234, SRG-OS-000327-GPOS-00127, RHEL-07-030310, Req-10.2.2, 5.2.10

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function perform_audit_rules_privileged_commands_remediation {
    #
    # Load function arguments into local variables
    local tool="$1"
    local min_auid="$2"

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
            echo "Usage: perform_audit_rules_privileged_commands_remediation 'auditctl | augenrules' '500 | 1000'"
            echo "Aborting."
            exit 1
    fi

    declare -a files_to_inspect=()

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then:
    # * add '/etc/audit/audit.rules'to the list of files to be inspected,
    # * specify '/etc/audit/audit.rules' as the output audit file, where
    #   missing rules should be inserted
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("/etc/audit/audit.rules")
            output_audit_file="/etc/audit/audit.rules"
    #
    # If the audit tool is 'augenrules', then:
    # * add '/etc/audit/rules.d/*.rules' to the list of files to be inspected
    #   (split by newline),
    # * specify /etc/audit/rules.d/privileged.rules' as the output file, where
    #   missing rules should be inserted
    elif [ "$tool" == 'augenrules' ]
    then
            IFS=$'\n' files_to_inspect=($(find /etc/audit/rules.d -maxdepth 1 -type f -name *.rules -print))
            output_audit_file="/etc/audit/rules.d/privileged.rules"
    fi

    # Obtain the list of SUID/SGID binaries on the particular system (split by newline)
    # into privileged_binaries array
    IFS=$'\n' privileged_binaries=($(find / -xdev -type f -perm -4000 -o -type f -perm -2000 2>/dev/null))

    # Keep list of SUID/SGID binaries that have been already handled within some previous iteration
    declare -a sbinaries_to_skip=()

    # For each found sbinary in privileged_binaries list
    for sbinary in "${privileged_binaries[@]}"
    do

            # Replace possible slash '/' character in sbinary definition so we could use it in sed expressions below
            sbinary_esc=${sbinary//$'/'/$'\/'}
            # Check if this sbinary wasn't already handled in some of the previous iterations
            # Return match only if whole sbinary definition matched (not in the case just prefix matched!!!)
            if [[ $(sed -ne "/${sbinary_esc}$/p" <<< ${sbinaries_to_skip[@]}) ]]
            then
                    # If so, don't process it second time & go to process next sbinary
                    continue
            fi

            # Reset the counter of inspected files when starting to check
            # presence of existing audit rule for new sbinary
            local count_of_inspected_files=0

            # For each audit rules file from the list of files to be inspected
            for afile in "${files_to_inspect[@]}"
            do

                    # Search current audit rules file's content for match. Match criteria:
                    # * existing rule is for the same SUID/SGID binary we are currently processing (but
                    #   can contain multiple -F path= elements covering multiple SUID/SGID binaries)
                    # * existing rule contains all arguments from expected rule form (though can contain
                    #   them in arbitrary order)

                    base_search=$(sed -e "/-a always,exit/!d" -e "/-F path=${sbinary_esc}$/!d"   \
                                      -e "/-F path=[^[:space:]]\+/!d" -e "/-F perm=.*/!d"       \
                                      -e "/-F auid>=${min_auid}/!d" -e "/-F auid!=4294967295/!d"  \
                                      -e "/-k privileged/!d" $afile)

                    # Increase the count of inspected files for this sbinary
                    count_of_inspected_files=$((count_of_inspected_files + 1))

                    # Define expected rule form for this binary
                    expected_rule="-a always,exit -F path=${sbinary} -F perm=x -F auid>=${min_auid} -F auid!=4294967295 -k privileged"

                    # Require execute access type to be set for existing audit rule
                    exec_access='x'

                    # Search current audit rules file's content for presence of rule pattern for this sbinary
                    if [[ $base_search ]]
                    then

                            # Current audit rules file already contains rule for this binary =>
                            # Store the exact form of found rule for this binary for further processing
                            concrete_rule=$base_search

                            # Select all other SUID/SGID binaries possibly also present in the found rule
                            IFS=$'\n' handled_sbinaries=($(grep -o -e "-F path=[^[:space:]]\+" <<< $concrete_rule))
                            IFS=$' ' handled_sbinaries=(${handled_sbinaries[@]//-F path=/})

                            # Merge the list of such SUID/SGID binaries found in this iteration with global list ignoring duplicates
                            sbinaries_to_skip=($(for i in "${sbinaries_to_skip[@]}" "${handled_sbinaries[@]}"; do echo $i; done | sort -du))

                            # Separate concrete_rule into three sections using hash '#'
                            # sign as a delimiter around rule's permission section borders
                            concrete_rule=$(echo $concrete_rule | sed -n "s/\(.*\)\+\(-F perm=[rwax]\+\)\+/\1#\2#/p")

                            # Split concrete_rule into head, perm, and tail sections using hash '#' delimiter
                            IFS=$'#' read rule_head rule_perm rule_tail <<<  "$concrete_rule"

                            # Extract already present exact access type [r|w|x|a] from rule's permission section
                            access_type=${rule_perm//-F perm=/}

                            # Verify current permission access type(s) for rule contain 'x' (execute) permission
                            if ! grep -q "$exec_access" <<< "$access_type"
                            then

                                    # If not, append the 'x' (execute) permission to the existing access type bits
                                    access_type="$access_type$exec_access"
                                    # Reconstruct the permissions section for the rule
                                    new_rule_perm="-F perm=$access_type"
                                    # Update existing rule in current audit rules file with the new permission section
                                    sed -i "s#${rule_head}\(.*\)${rule_tail}#${rule_head}${new_rule_perm}${rule_tail}#" $afile

                            fi

                    # If the required audit rule for particular sbinary wasn't found yet, insert it under following conditions:
                    #
                    # * in the "auditctl" mode of operation insert particular rule each time
                    #   (because in this mode there's only one file -- /etc/audit/audit.rules to be inspected for presence of this rule),
                    #
                    # * in the "augenrules" mode of operation insert particular rule only once and only in case we have already
                    #   searched all of the files from /etc/audit/rules.d/*.rules location (since that audit rule can be defined
                    #   in any of those files and if not, we want it to be inserted only once into /etc/audit/rules.d/privileged.rules file)
                    #
                    elif [ "$tool" == "auditctl" ] || [[ "$tool" == "augenrules" && $count_of_inspected_files -eq "${#files_to_inspect[@]}" ]]
                    then

                            # Current audit rules file's content doesn't contain expected rule for this
                            # SUID/SGID binary yet => append it
                            echo $expected_rule >> $output_audit_file
                    fi

            done

    done

    }

    perform_audit_rules_privileged_commands_remediation "auditctl" "1000"
    perform_audit_rules_privileged_commands_remediation "augenrules" "1000"

#### Ensure auditd Collects Information on Exporting to Media (successful) [ref]rule

At a minimum the audit system should collect media exportation events for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`, setting ARCH to either b32 or b64 as appropriate for your system:

    -a always,exit -F arch=ARCH -S mount -F auid>=1000 -F auid!=4294967295 -k export

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file, setting ARCH to either b32 or b64 as appropriate for your system:

    -a always,exit -F arch=ARCH -S mount -F auid>=1000 -F auid!=4294967295 -k export

Rationale:

The unauthorized exportation of data to external media could result in an information leak where classified information, Privacy Act information, and intellectual property could be lost. An audit trail should be created each time a filesystem is mounted to help identify and guard against information loss.

Severity: medium

Identifiers: CCE-27447-2

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-3(1), AU-12(a), AU-12(c), IR-5, 135, 2884, SRG-OS-000042-GPOS-00020, SRG-OS-000392-GPOS-00172, RHEL-07-030530, Req-10.2.7, 5.2.13

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation of the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=$ARCH -S .* -F auid>=1000 -F auid!=4294967295 -k *"
    	GROUP="mount"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S mount -F auid>=1000 -F auid!=4294967295 -k export"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Ensure auditd Collects File Deletion Events by User [ref]rule

At a minimum the audit system should collect file deletion events for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`, setting ARCH to either b32 or b64 as appropriate for your system:

    -a always,exit -F arch=ARCH -S rmdir -S unlink -S unlinkat -S rename -S renameat -F auid>=1000 -F auid!=4294967295 -k delete

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file, setting ARCH to either b32 or b64 as appropriate for your system:

    -a always,exit -F arch=ARCH -S rmdir -S unlink -S unlinkat -S rename -S renameat -F auid>=1000 -F auid!=4294967295 -k delete

Rationale:

Auditing file deletions will create an audit trail for files that are removed from the system. The audit trail could aid in system troubleshooting, as well as, detecting malicious processes that attempt to delete log files to conceal their presence.

Severity: medium

Identifiers: CCE-27206-2

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 366, SRG-OS-000480-GPOS-00227, RHEL-07-030750, Req-10.2.7, 5.2.14

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for the syscall rule
    # Retrieve hardware architecture of the underlying system
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b32" "b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=$ARCH -S .* -F auid>=1000 -F auid!=4294967295 -k *"
    	# Use escaped BRE regex to specify rule group
    	GROUP="\(rmdir\|unlink\|rename\)"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S rmdir -S unlink -S unlinkat -S rename -S renameat -F auid>=1000 -F auid!=4294967295 -k delete"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

#### Ensure auditd Collects System Administrator Actions [ref]rule

At a minimum the audit system should collect administrator actions for all users and root. If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d`:

    -w /etc/sudoers -p wa -k actions

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file:

    -w /etc/sudoers -p wa -k actions

Rationale:

The actions taken by system administrators should be audited to keep a record of what was executed on the system, as well as, for accountability purposes.

Severity: low

Identifiers: CCE-27461-3

References: AC-2(7)(b), AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126, Req-10.2.2, Req-10.2.5.b

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/etc/sudoers" "wa" "actions"
    fix_audit_watch_rule "augenrules" "/etc/sudoers" "wa" "actions"

#### Ensure auditd Collects Information on Kernel Module Loading and Unloading [ref]rule

If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following lines to a file with suffix `.rules` in the directory `/etc/audit/rules.d` to capture kernel module loading and unloading events, setting ARCH to either b32 or b64 as appropriate for your system:

    -w /usr/sbin/insmod -p x -k modules
    -w /usr/sbin/rmmod -p x -k modules
    -w /usr/sbin/modprobe -p x -k modules
    -a always,exit -F arch=ARCH -S init_module -S delete_module -k modules

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following lines to `/etc/audit/audit.rules` file in order to capture kernel module loading and unloading events, setting ARCH to either b32 or b64 as appropriate for your system:

    -w /usr/sbin/insmod -p x -k modules
    -w /usr/sbin/rmmod -p x -k modules
    -w /usr/sbin/modprobe -p x -k modules
    -a always,exit -F arch=ARCH -S init_module -S delete_module -k modules

Rationale:

The addition/removal of kernel modules can be used to alter the behavior of the kernel and potentially introduce malicious code into kernel space. It is important to have an audit trail of modules that have been introduced into the kernel.

Severity: medium

Identifiers: CCE-27129-6

References: AC-17(7), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 172, SRG-OS-000471-GPOS-00216, SRG-OS-000477, GPOS-00222, RHEL-07-030670, Req-10.2.7, 5.2.17

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # First perform the remediation of the syscall rule
    # Retrieve hardware architecture of the underlying system
    # Note: 32-bit kernel modules can't be loaded / unloaded on 64-bit kernel =>
    #       it's not required on a 64-bit system to check also for the presence
    #       of 32-bit's equivalent of the corresponding rule. Therefore for
    #       each system it's enought to check presence of system's native rule form.
    [ $(getconf LONG_BIT) = "32" ] && RULE_ARCHS=("b32") || RULE_ARCHS=("b64")

    for ARCH in "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit -F arch=$ARCH -S .* -k *"
    	# Use escaped BRE regex to specify rule group
    	GROUP="\(init\|delete\)_module"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S init_module -S delete_module -k modules"
    	# Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_syscall_rule {

    # Load function arguments into local variables
    local tool="$1"
    local pattern="$2"
    local group="$3"
    local arch="$4"
    local full_rule="$5"

    # Check sanity of the input
    if [ $# -ne "5" ]
    then
            echo "Usage: fix_audit_syscall_rule 'tool' 'pattern' 'group' 'arch' 'full rule'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    #  Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #        auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #        augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #        augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    #
    declare -a files_to_inspect

    # First check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # file to the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules' )
    # If audit tool is 'augenrules', then check if the audit rule is defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to the list for inspection
    # If rule isn't defined yet, add '/etc/audit/rules.d/$key.rules' to the list for inspection
    elif [ "$tool" == 'augenrules' ]
    then
            # Extract audit $key from audit rule so we can use it later
            key=$(expr "$full_rule" : '.*-k[[:space:]]\([^[:space:]]\+\)')
            # Check if particular audit rule is already defined
            IFS=$'\n' matches=($(sed -s -n -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d;F" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            for match in "${matches[@]}"
            do
                    files_to_inspect=("${files_to_inspect[@]}" "${match}")
            done
            # Case when particular rule isn't defined in /etc/audit/rules.d/*.rules yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    #
    # Indicator that we want to append $full_rule into $audit_file by default
    local append_expected_rule=0

    for audit_file in "${files_to_inspect[@]}"
    do

            # Filter existing $audit_file rules' definitions to select those that:
            # * follow the rule pattern, and
            # * meet the hardware architecture requirement, and
            # * are current syscall group specific
            IFS=$'\n' existing_rules=($(sed -e "/${pattern}/!d" -e "/${arch}/!d" -e "/${group}/!d"  "$audit_file"))
            # Reset IFS back to default
            unset $IFS

            # Process rules found case-by-case
            for rule in "${existing_rules[@]}"
            do
                    # Found rule is for same arch & key, but differs (e.g. in count of -S arguments)
                    if [ "${rule}" != "${full_rule}" ]
                    then
                            # If so, isolate just '(-S \w)+' substring of that rule
                            rule_syscalls=$(echo $rule | grep -o -P '(-S \w+ )+')
                            # Check if list of '-S syscall' arguments of that rule is subset
                            # of '-S syscall' list of expected $full_rule
                            if grep -q -- "$rule_syscalls" <<< "$full_rule"
                            then
                                    # Rule is covered (i.e. the list of -S syscalls for this rule is
                                    # subset of -S syscalls of $full_rule => existing rule can be deleted
                                    # Thus delete the rule from audit.rules & our array
                                    sed -i -e "/$rule/d" "$audit_file"
                                    existing_rules=("${existing_rules[@]//$rule/}")
                            else
                                    # Rule isn't covered by $full_rule - it besides -S syscall arguments
                                    # for this group contains also -S syscall arguments for other syscall
                                    # group. Example: '-S lchown -S fchmod -S fchownat' => group='chown'
                                    # since 'lchown' & 'fchownat' share 'chown' substring
                                    # Therefore:
                                    # * 1) delete the original rule from audit.rules
                                    # (original '-S lchown -S fchmod -S fchownat' rule would be deleted)
                                    # * 2) delete the -S syscall arguments for this syscall group, but
                                    # keep those not belonging to this syscall group
                                    # (original '-S lchown -S fchmod -S fchownat' would become '-S fchmod'
                                    # * 3) append the modified (filtered) rule again into audit.rules
                                    # if the same rule not already present
                                    #
                                    # 1) Delete the original rule
                                    sed -i -e "/$rule/d" "$audit_file"
                                    # 2) Delete syscalls for this group, but keep those from other groups
                                    # Convert current rule syscall's string into array splitting by '-S' delimiter
                                    IFS=$'-S' read -a rule_syscalls_as_array <<< "$rule_syscalls"
                                    # Reset IFS back to default
                                    unset $IFS
                                    # Declare new empty string to hold '-S syscall' arguments from other groups
                                    new_syscalls_for_rule=''
                                    # Walk through existing '-S syscall' arguments
                                    for syscall_arg in "${rule_syscalls_as_array[@]}"
                                    do
                                            # Skip empty $syscall_arg values
                                            if [ "$syscall_arg" == '' ]
                                            then
                                                    continue
                                            fi
                                            # If the '-S syscall' doesn't belong to current group add it to the new list
                                            # (together with adding '-S' delimiter back for each of such item found)
                                            if grep -q -v -- "$group" <<< "$syscall_arg"
                                            then
                                                    new_syscalls_for_rule="$new_syscalls_for_rule -S $syscall_arg"
                                            fi
                                    done
                                    # Replace original '-S syscall' list with the new one for this rule
                                    updated_rule=${rule//$rule_syscalls/$new_syscalls_for_rule}
                                    # Squeeze repeated whitespace characters in rule definition (if any) into one
                                    updated_rule=$(echo "$updated_rule" | tr -s '[:space:]')
                                    # 3) Append the modified / filtered rule again into audit.rules
                                    #    (but only in case it's not present yet to prevent duplicate definitions)
                                    if ! grep -q -- "$updated_rule" "$audit_file"
                                    then
                                            echo "$updated_rule" >> "$audit_file"
                                    fi
                            fi
                    else
                            # $audit_file already contains the expected rule form for this
                            # architecture & key => don't insert it second time
                            append_expected_rule=1
                    fi
            done

            # We deleted all rules that were subset of the expected one for this arch & key.
            # Also isolated rules containing system calls not from this system calls group.
            # Now append the expected rule if it's not present in $audit_file yet
            if [[ ${append_expected_rule} -eq "0" ]]
            then
                    echo "$full_rule" >> "$audit_file"
            fi
    done

    }

    	fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    	fix_audit_syscall_rule "augenrules" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

    # Then perform the remediations for the watch rules
    # Perform the remediation for both possible tools: 'auditctl' and 'augenrules'

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/usr/sbin/insmod" "x" "modules"
    fix_audit_watch_rule "augenrules" "/usr/sbin/insmod" "x" "modules"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/usr/sbin/rmmod" "x" "modules"
    fix_audit_watch_rule "augenrules" "/usr/sbin/rmmod" "x" "modules"

    function fix_audit_watch_rule {

    # Load function arguments into local variables
    local tool="$1"
    local path="$2"
    local required_access_bits="$3"
    local key="$4"

    # Check sanity of the input
    if [ $# -ne "4" ]
    then
            echo "Usage: fix_audit_watch_rule 'tool' 'path' 'bits' 'key'"
            echo "Aborting."
            exit 1
    fi

    # Create a list of audit *.rules files that should be inspected for presence and correctness
    # of a particular audit rule. The scheme is as follows:
    #
    # -----------------------------------------------------------------------------------------
    # Tool used to load audit rules | Rule already defined  |  Audit rules file to inspect    |
    # -----------------------------------------------------------------------------------------
    #       auditctl                |     Doesn't matter    |  /etc/audit/audit.rules         |
    # -----------------------------------------------------------------------------------------
    #       augenrules              |          Yes          |  /etc/audit/rules.d/*.rules     |
    #       augenrules              |          No           |  /etc/audit/rules.d/$key.rules  |
    # -----------------------------------------------------------------------------------------
    declare -a files_to_inspect

    # Check sanity of the specified audit tool
    if [ "$tool" != 'auditctl' ] && [ "$tool" != 'augenrules' ]
    then
            echo "Unknown audit rules loading tool: $1. Aborting."
            echo "Use either 'auditctl' or 'augenrules'!"
            exit 1
    # If the audit tool is 'auditctl', then add '/etc/audit/audit.rules'
    # into the list of files to be inspected
    elif [ "$tool" == 'auditctl' ]
    then
            files_to_inspect=("${files_to_inspect[@]}" '/etc/audit/audit.rules')
    # If the audit is 'augenrules', then check if rule is already defined
    # If rule is defined, add '/etc/audit/rules.d/*.rules' to list of files for inspection.
    # If rule isn't defined, add '/etc/audit/rules.d/$key.rules' to list of files for inspection.
    elif [ "$tool" == 'augenrules' ]
    then
            # Case when particular audit rule is already defined in some of /etc/audit/rules.d/*.rules file
            # Get pair -- filepath : matching_row into @matches array
            IFS=$'\n' matches=($(grep -P "[\s]*-w[\s]+$path" /etc/audit/rules.d/*.rules))
            # Reset IFS back to default
            unset $IFS
            # For each of the matched entries
            for match in "${matches[@]}"
            do
                    # Extract filepath from the match
                    rulesd_audit_file=$(echo $match | cut -f1 -d ':')
                    # Append that path into list of files for inspection
                    files_to_inspect=("${files_to_inspect[@]}" "$rulesd_audit_file")
            done
            # Case when particular audit rule isn't defined yet
            if [ ${#files_to_inspect[@]} -eq "0" ]
            then
                    # Append '/etc/audit/rules.d/$key.rules' into list of files for inspection
                    files_to_inspect="/etc/audit/rules.d/$key.rules"
                    # If the $key.rules file doesn't exist yet, create it with correct permissions
                    if [ ! -e "$files_to_inspect" ]
                    then
                            touch "$files_to_inspect"
                            chmod 0640 "$files_to_inspect"
                    fi
            fi
    fi

    # Finally perform the inspection and possible subsequent audit rule
    # correction for each of the files previously identified for inspection
    for audit_rules_file in "${files_to_inspect[@]}"
    do

            # Check if audit watch file system object rule for given path already present
            if grep -q -P -- "[\s]*-w[\s]+$path" "$audit_rules_file"
            then
                    # Rule is found => verify yet if existing rule definition contains
                    # all of the required access type bits

                    # Escape slashes in path for use in sed pattern below
                    local esc_path=${path//$'/'/$'\/'}
                    # Define BRE whitespace class shortcut
                    local sp="[[:space:]]"
                    # Extract current permission access types (e.g. -p [r|w|x|a] values) from audit rule
                    current_access_bits=$(sed -ne "s/$sp*-w$sp\+$esc_path$sp\+-p$sp\+\([rxwa]\{1,4\}\).*/\1/p" "$audit_rules_file")
                    # Split required access bits string into characters array
                    # (to check bit's presence for one bit at a time)
                    for access_bit in $(echo "$required_access_bits" | grep -o .)
                    do
                            # For each from the required access bits (e.g. 'w', 'a') check
                            # if they are already present in current access bits for rule.
                            # If not, append that bit at the end
                            if ! grep -q "$access_bit" <<< "$current_access_bits"
                            then
                                    # Concatenate the existing mask with the missing bit
                                    current_access_bits="$current_access_bits$access_bit"
                            fi
                    done
                    # Propagate the updated rule's access bits (original + the required
                    # ones) back into the /etc/audit/audit.rules file for that rule
                    sed -i "s/\($sp*-w$sp\+$esc_path$sp\+-p$sp\+\)\([rxwa]\{1,4\}\)\(.*\)/\1$current_access_bits\3/" "$audit_rules_file"
            else
                    # Rule isn't present yet. Append it at the end of $audit_rules_file file
                    # with proper key

                    echo "-w $path -p $required_access_bits -k $key" >> "$audit_rules_file"
            fi
    done
    }

    fix_audit_watch_rule "auditctl" "/usr/sbin/modprobe" "x" "modules"
    fix_audit_watch_rule "augenrules" "/usr/sbin/modprobe" "x" "modules"

#### Make the auditd Configuration Immutable [ref]rule

If the `auditd` daemon is configured to use the `augenrules` program to read audit rules during daemon startup (the default), add the following line to a file with suffix `.rules` in the directory `/etc/audit/rules.d` in order to make the auditd configuration immutable:

    -e 2

If the `auditd` daemon is configured to use the `auditctl` utility to read audit rules during daemon startup, add the following line to `/etc/audit/audit.rules` file in order to make the auditd configuration immutable:

    -e 2

With this setting, a reboot will be required to change any audit rules. Rationale:

Making the audit configuration immutable prevents accidental as well as malicious modification of the audit rules, although it may be problematic if legitimate changes are needed during system operation

Severity: low

Identifiers: CCE-27097-5

References: AC-6, AU-1(b), AU-2(a), AU-2(c), AU-2(d), IR-5, Req-10.5.2, 5.2.18

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Traverse all of:
    #
    # /etc/audit/audit.rules,			(for auditctl case)
    # /etc/audit/rules.d/*.rules			(for augenrules case)
    #
    # files to check if '-e .*' setting is present in that '*.rules' file already.
    # If found, delete such occurrence since auditctl(8) manual page instructs the
    # '-e 2' rule should be placed as the last rule in the configuration
    find /etc/audit /etc/audit/rules.d -maxdepth 1 -type f -name *.rules -exec sed -i '/-e[[:space:]]\+.*/d' {} ';'

    # Append '-e 2' requirement at the end of both:
    # * /etc/audit/audit.rules file 		(for auditctl case)
    # * /etc/audit/rules.d/immutable.rules		(for augenrules case)

    for AUDIT_FILE in "/etc/audit/audit.rules" "/etc/audit/rules.d/immutable.rules"
    do
    	echo '' >> $AUDIT_FILE
    	echo '# Set the audit.rules configuration immutable per security requirements' >> $AUDIT_FILE
    	echo '# Reboot is required to change audit rules once this setting is applied' >> $AUDIT_FILE
    	echo '-e 2' >> $AUDIT_FILE
    done

#### Enable auditd Service [ref]rule

The `auditd` service is an essential userspace component of the Linux Auditing System, as it is responsible for writing audit records to disk. The `auditd` service can be enabled with the following command:

    $ sudo systemctl enable auditd.service

Rationale:

Without establishing what type of events occurred, it would be difficult to establish, correlate, and investigate the events leading up to an outage or attack.
Ensuring the `auditd` service is active ensures audit records generated by the kernel are appropriately recorded.

Severity: high

Identifiers: CCE-27407-6

References: AU-3, AC-17(1), AU-1(b), AU-10, AU-12(a), AU-12(c), AU-14(1), IR-5, 126, 131, SRG-OS-000038-GPOS-00016, SRG-OS-000039-GPOS-00017, SRG-OS-000042-GPOS-00021, SRG-OS-000254-GPOS-00095, SRG-OS-000255-GPOS-00096, RHEL-07-030010, Req-10, 5.2.2

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

    service_command enable auditd

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    - name: Enable service auditd
      service:
        name="{{item}}"
        enabled="yes"
        state="started"
      with_items:
        - auditd

#### Enable Auditing for Processes Which Start Prior to the Audit Daemon [ref]rule

To ensure all processes can be audited, even those which start prior to the audit daemon, add the argument `audit=1` to the default GRUB 2 command line for the Linux operating system in `/etc/default/grub`, in the manner below:

    GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=VolGroup/LogVol06 rd.lvm.lv=VolGroup/lv_swap rhgb quiet rd.shell=0 audit=1"

Warning: The GRUB 2 configuration file, `grub.cfg`, is automatically updated each time a new kernel is installed. Note that any changes to `/etc/default/grub` require rebuilding the `grub.cfg` file. To update the GRUB 2 configuration file manually, use the

    grub2-mkconfig -o

command as follows:

- On BIOS-based machines, issue the following command as `root`:

      ~]# grub2-mkconfig -o /boot/grub2/grub.cfg

- On UEFI-based machines, issue the following command as `root`:

      ~]# grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg

Rationale:

Each process on the system carries an "auditable" flag which indicates whether its activities can be audited. Although `auditd` takes care of enabling this for all processes which launch after it does, adding the kernel argument ensures it is set for every process during boot.

Severity: medium

Identifiers: CCE-27212-0

References: AC-17(1), AU-14(1), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-10, IR-5, 1464, 130, Req-10.3, 5.2.3

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    # Correct the form of default kernel command line in /etc/default/grub
    grep -q ^GRUB_CMDLINE_LINUX=\".*audit=0.*\" /etc/default/grub && \
      sed -i "s/audit=[^[:space:]\+]/audit=1/g" /etc/default/grub
    if ! [ $? -eq 0 ]; then
      sed -i "s/\(GRUB_CMDLINE_LINUX=\)\"\(.*\)\"/\1\"\2 audit=1\"/" /etc/default/grub
    fi

    # Correct the form of kernel command line for each installed kernel
    # in the bootloader
    /sbin/grubby --update-kernel=ALL --args="audit=1"

### Services [ref]group

The best protection against vulnerable software is running less software. This section describes how to review the software which Red Hat Enterprise Linux 7 installs on a system and disable software which is not needed. It then enumerates the software packages installed on a default Red Hat Enterprise Linux 7 system and provides guidance about which ones can be safely disabled.
Red Hat Enterprise Linux 7 provides a convenient minimal install option that essentially installs the bare necessities for a functional system. When building Red Hat Enterprise Linux 7 systems, it is highly recommended to select the minimal packages and then build up the system from there.

contains 63 rules

### Obsolete Services [ref]group

This section discusses a number of network-visible services which have historically caused problems for system security, and for which disabling or severely limiting the service has been the best available guidance for some time. As a result of this, many of these services are not installed as part of Red Hat Enterprise Linux 7 by default.
Organizations which are running these services should switch to more secure equivalents as soon as possible. If it remains absolutely necessary to run one of these services for legacy reasons, care should be taken to restrict the service as much as possible, for instance by configuring host firewall software such as `firewalld` to restrict access to the vulnerable service to only those remote hosts which have a known need to use it.

contains 18 rules

### Xinetd [ref]group

The `xinetd` service acts as a dedicated listener for some network services (mostly, obsolete ones) and can be used to provide access controls and perform some logging. It has been largely obsoleted by other features, and it is not installed by default. The older Inetd service is not even available as part of Red Hat Enterprise Linux 7.

contains 2 rules

#### Disable xinetd Service [ref]rule

The `xinetd` service can be disabled with the following command:

    $ sudo systemctl disable xinetd.service

Rationale:

The xinetd service provides a dedicated listener service for some programs, which is no longer necessary for commonly-used network services. Disabling it ensures that these uncommon services are not running, and also prevents attacks against xinetd itself.

Severity: medium

Identifiers: CCE-27443-1

References: AC-17(8), CM-7, 305

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

    service_command disable xinetd

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Disable service xinetd
      service:
        name="{{item}}"
        enabled="no"
        state="stopped"
      with_items:
        - xinetd

#### Uninstall xinetd Package [ref]rule

The `xinetd` package can be uninstalled with the following command:

    $ sudo yum erase xinetd

Rationale:

Removing the `xinetd` package decreases the risk of the xinetd service's accidental (or intentional) activation.

Severity: low

Identifiers: CCE-27354-0

References: AC-17(8), CM-7, 305, 2.1.11

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command remove xinetd

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Ensure xinetd is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - xinetd

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include remove_xinetd

    class remove_xinetd {
      package { 'xinetd':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    package -remove=xinetd

### Telnet [ref]group

The telnet protocol does not provide confidentiality or integrity for information transmitted on the network. This includes authentication information such as passwords. Organizations which use telnet should be actively working to migrate to a more secure protocol.

contains 3 rules

#### Disable telnet Service [ref]rule

The `telnet` service configuration file `/etc/xinetd.d/telnet` is not created automatically. If it was created manually, check the `/etc/xinetd.d/telnet` file and ensure that `disable = no` is changed to read `disable = yes` as follows below:

    # description: The telnet server serves telnet sessions; it uses \\
    #       unencrypted username/password pairs for authentication.
    service telnet
    {
            flags           = REUSE
            socket_type     = stream

            wait            = no
            user            = root
            server          = /usr/sbin/in.telnetd
            log_on_failure  += USERID
            disable         = yes
    }

If the `/etc/xinetd.d/telnet` file does not exist, make sure that the activation of the `telnet` service on system boot is disabled via the following command: The `rexec` socket can be disabled with the following command:

    $ sudo systemctl disable rexec.socket

Rationale:

The telnet protocol uses unencrypted network communication, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network. The telnet protocol is also subject to man-in-the-middle attacks.

Severity: high

Identifiers: CCE-27401-9

References: AC-17(8), CM-7, IA-5(1)(c), http://iase.disa.mil/stigs/cci/Pages/index.aspx

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    grep -qi disable /etc/xinetd.d/telnet && \
      sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/telnet

    #
    # Disable telnet.socket for all systemd targets
    #
    systemctl disable telnet.socket

    #
    # Stop telnet.socket if currently running
    #
    systemctl stop telnet.socket

#### Uninstall telnet-server Package [ref]rule

The `telnet-server` package can be uninstalled with the following command:

    $ sudo yum erase telnet-server

Rationale:

It is detrimental for operating systems to provide, or install by default, functionality exceeding requirements or mission objectives. These unnecessary capabilities are often overlooked and therefore may remain unsecure. They increase the risk to the platform by providing additional attack vectors.
The telnet service provides an unencrypted remote access service which does not provide for the confidentiality and integrity of user passwords or the remote session. If a privileged user were to login using this service, the privileged user password could be compromised.
Removing the `telnet-server` package decreases the risk of the telnet service's accidental (or intentional) activation.

Severity: high

Identifiers: CCE-27165-0

References: AC-17(8), CM-7(a), 381, SRG-OS-000095-GPOS-00049, RHEL-07-021910, 2.1.1

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command remove telnet-server

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Ensure telnet-server is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - telnet-server

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include remove_telnet-server

    class remove_telnet-server {
      package { 'telnet-server':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    package -remove=telnet-server

#### Remove telnet Clients [ref]rule

The telnet client allows users to start connections to other systems via the telnet protocol.

Rationale:

The `telnet` protocol is insecure and unencrypted. The use of an unencrypted transmission medium could allow an unauthorized user to steal credentials. The `ssh` package provides an encrypted session and stronger security and is included in Red Hat Enterprise Linux.

Severity: low

Identifiers: CCE-27305-2

References: 2.1.2

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command remove telnet

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Ensure telnet is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - telnet

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include remove_telnet

    class remove_telnet {
      package { 'telnet':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    package -remove=telnet

### Rlogin, Rsh, and Rexec [ref]group

The Berkeley r-commands are legacy services which allow cleartext remote access and have an insecure trust model.

contains 6 rules

#### Uninstall rsh-server Package [ref]rule

The `rsh-server` package can be uninstalled with the following command:

    $ sudo yum erase rsh-server

Rationale:

The `rsh-server` service provides unencrypted remote access service which does not provide for the confidentiality and integrity of user passwords or the remote session and has very weak authentication. If a privileged user were to login using this service, the privileged user password could be compromised. The `rsh-server` package provides several obsolete and insecure network services. Removing it decreases the risk of those services' accidental (or intentional) activation.

Severity: high

Identifiers: CCE-27342-5

References: AC-17(8), CM-7(a), 381, SRG-OS-000095-GPOS-00049, RHEL-07-020000, 2.1.3

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command remove rsh-server

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Ensure rsh-server is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - rsh-server

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include remove_rsh-server

    class remove_rsh-server {
      package { 'rsh-server':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    package -remove=rsh-server

#### Disable rexec Service [ref]rule

The `rexec` service, which is available with the `rsh-server` package and runs as a service through xinetd or separately as a systemd socket, should be disabled. If using xinetd, set `disable` to `yes` in `/etc/xinetd.d/rexec`. If using systemd, The `rexec` socket can be disabled with the following command:

    $ sudo systemctl disable rexec.socket

Rationale:

The rexec service uses unencrypted network communications, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network.

Severity: high

Identifiers: CCE-27408-4

References: AC-17(8), CM-7, 68, 1436

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    grep -qi disable /etc/xinetd.d/rexec && \
      sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/rexec

    #
    # Disable rexec.socket for all systemd targets
    #
    systemctl disable rexec.socket

    #
    # Stop rexec.socket if currently running
    #
    systemctl stop rexec.socket

#### Disable rsh Service [ref]rule

The `rsh` service, which is available with the `rsh-server` package and runs as a service through xinetd or separately as a systemd socket, should be disabled. If using xinetd, set `disable` to `yes` in `/etc/xinetd.d/rsh`. If using systemd, The `rsh` socket can be disabled with the following command:

    $ sudo systemctl disable rsh.socket

Rationale:

The rsh service uses unencrypted network communications, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network.

Severity: high

Identifiers: CCE-27337-5

References: AC-17(8), CM-7, IA-5(1)(c), 68, 1436

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    grep -qi disable /etc/xinetd.d/rsh && \
      sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/rsh

    #
    # Disable rsh.socket for all systemd targets
    #
    systemctl disable rsh.socket

    #
    # Stop rsh.socket if currently running
    #
    systemctl stop rsh.socket

#### Uninstall rsh Package [ref]rule

The `rsh` package contains the client commands for the rsh services

Rationale:

These legacy clients contain numerous security exposures and have been replaced with the more secure SSH package. Even if the server is removed, it is best to ensure the clients are also removed to prevent users from inadvertently attempting to use these commands and therefore exposing their credentials. Note that removing the `rsh` package removes the clients for `rsh`,`rcp`, and `rlogin`.

Severity: low

Identifiers: CCE-27274-0

References: 2.1.4

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command remove rsh

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Ensure rsh is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - rsh

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include remove_rsh

    class remove_rsh {
      package { 'rsh':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    package -remove=rsh

#### Disable rlogin Service [ref]rule

The `rlogin` service, which is available with the `rsh-server` package and runs as a service through xinetd or separately as a systemd socket, should be disabled. If using xinetd, set `disable` to `yes` in `/etc/xinetd.d/rlogin`. If using systemd, The `rlogin` socket can be disabled with the following command:

    $ sudo systemctl disable rlogin.socket

Rationale:

The rlogin service uses unencrypted network communications, which means that data from the login session, including passwords and all other information transmitted during the session, can be stolen by eavesdroppers on the network.

Severity: high

Identifiers: CCE-27336-7

References: AC-17(8), CM-7, IA-5(1)(c), 1436

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    grep -qi disable /etc/xinetd.d/rlogin && \
      sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/rlogin

    #
    # Disable rlogin.socket for all systemd targets
    #
    systemctl disable rlogin.socket

    #
    # Stop rlogin.socket if currently running
    #
    systemctl stop rlogin.socket

#### Remove Rsh Trust Files [ref]rule

The files `/etc/hosts.equiv` and `~/.rhosts` (in each user's home directory) list remote hosts and users that are trusted by the local system when using the rshd daemon. To remove these files, run the following command to delete them from any location:

    $ sudo rm /etc/hosts.equiv

    $ rm ~/.rhosts

Rationale:

Trust files are convenient, but when used in conjunction with the R-services, they can allow unauthenticated access to a system.

Severity: high

Identifiers: CCE-27406-8

References: AC-17(8), CM-7, 1436

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    find -type f -name .rhosts -exec rm -f '{}' \;
    rm /etc/hosts.equiv

### NIS [ref]group

The Network Information Service (NIS), also known as 'Yellow Pages' (YP), and its successor NIS+ have been made obsolete by Kerberos, LDAP, and other modern centralized authentication services. NIS should not be used because it suffers from security problems inherent in its design, such as inadequate protection of important authentication information.

contains 3 rules

#### Uninstall ypserv Package [ref]rule

The `ypserv` package can be uninstalled with the following command:

    $ sudo yum erase ypserv

Rationale:

The NIS service provides an unencrypted authentication service which does not provide for the confidentiality and integrity of user passwords or the remote session. Removing the `ypserv` package decreases the risk of the accidental (or intentional) activation of NIS or NIS+ services.

Severity: high

Identifiers: CCE-27399-5

References: AC-17(8), CM-7(a), 381, SRG-OS-000095-GPOS-00049, RHEL-07-020010, 2.1.6

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command remove ypserv

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Ensure ypserv is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - ypserv

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include remove_ypserv

    class remove_ypserv {
      package { 'ypserv':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    package -remove=ypserv

#### Disable ypbind Service [ref]rule

The `ypbind` service, which allows the system to act as a client in a NIS or NIS+ domain, should be disabled. The `ypbind` service can be disabled with the following command:

    $ sudo systemctl disable ypbind.service

Rationale:

Disabling the `ypbind` service ensures the system is not acting as a client in a NIS or NIS+ domain.

Severity: medium

Identifiers: CCE-27385-4

References: AC-17(8), CM-7, 305

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

    service_command disable ypbind

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Disable service ypbind
      service:
        name="{{item}}"
        enabled="no"
        state="stopped"
      with_items:
        - ypbind

#### Remove NIS Client [ref]rule

The Network Information Service (NIS), formerly known as Yellow Pages, is a client-server directory service protocol used to distribute system configuration files. The NIS client (`ypbind`) was used to bind a machine to an NIS server and receive the distributed configuration files.

Rationale:

The NIS service is inherently an insecure system that has been vulnerable to DOS attacks, buffer overflows and has poor authentication for querying NIS maps. NIS generally has been replaced by such protocols as Lightweight Directory Access Protocol (LDAP). It is recommended that the service be removed.

Severity: low

Identifiers: CCE-27396-1

References: 2.1.5

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command remove ypbind

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Ensure ypbind is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - ypbind

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include remove_ypbind

    class remove_ypbind {
      package { 'ypbind':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    package -remove=ypbind

### TFTP Server [ref]group

TFTP is a lightweight version of the FTP protocol which has traditionally been used to configure networking equipment. However, TFTP provides little security, and modern versions of networking operating systems frequently support configuration via SSH or other more secure protocols. A TFTP server should be run only if no more secure method of supporting existing equipment can be found.

contains 2 rules

#### Uninstall tftp-server Package [ref]rule

The `tftp-server` package can be removed with the following command:

    $ sudo yum erase tftp-server

Rationale:

Removing the `tftp-server` package decreases the risk of the accidental (or intentional) activation of tftp services.
If TFTP is required for operational support (such as transmission of router configurations), its use must be documented with the Information Systems Securty Manager (ISSM), restricted to only authorized personnel, and have access control rules established.

Severity: high

Identifiers: CCE-80213-2

References: AC-17(8), CM-6(c), CM-7, 318, 368, 1812, 1813, 1814, SRG-OS-000480-GPOS-00227, RHEL-07-040500, 2.1.8

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command remove tftp-server

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Ensure tftp-server is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - tftp-server

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include remove_tftp-server

    class remove_tftp-server {
      package { 'tftp-server':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    package -remove=tftp-server

#### Ensure tftp Daemon Uses Secure Mode [ref]rule

If running the `tftp` service is necessary, it should be configured to change its root directory at startup. To do so, ensure `/etc/xinetd.d/tftp` includes `-s` as a command line argument, as shown in the following example (which is also the default):

    server_args = -s /var/lib/tftpboot

Rationale:

Using the `-s` option causes the TFTP service to only serve files from the given directory. Serving files from an intentionally-specified directory reduces the risk of sharing files which should remain private.

Severity: medium

Identifiers: CCE-80214-0

References: AC-6, AC-17(8), CM-7, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040520

### Chat/Messaging Services [ref]group

The talk software makes it possible for users to send and receive messages across systems through a terminal session.

contains 2 rules

#### Uninstall talk-server Package [ref]rule

The `talk-server` package can be removed with the following command:

    $ sudo yum erase talk-server

Rationale:

The talk software presents a security risk as it uses unencrypted protocols for communications. Removing the `talk-server` package decreases the risk of the accidental (or intentional) activation of talk services.

Severity: medium

Identifiers: CCE-27210-4

References: 2.1.10

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command remove talk-server

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Ensure talk-server is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - talk-server

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include remove_talk-server

    class remove_talk-server {
      package { 'talk-server':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    package -remove=talk-server

#### Uninstall talk Package [ref]rule

The `talk` package contains the client program for the Internet talk protocol, which allows the user to chat with other users on different systems. Talk is a communication program which copies lines from one terminal to the terminal of another user. The `talk` package can be removed with the following command:

    $ sudo yum erase talk

Rationale:

The talk software presents a security risk as it uses unencrypted protocols for communications. Removing the `talk` package decreases the risk of the accidental (or intentional) activation of talk client program.

Severity: low

Identifiers: CCE-27432-4

References: 2.1.9

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command remove talk

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Ensure talk is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - talk

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include remove_talk

    class remove_talk {
      package { 'talk':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    package -remove=talk

### Base Services [ref]group

This section addresses the base services that are installed on a Red Hat Enterprise Linux 7 default installation which are not covered in other sections. Some of these services listen on the network and should be treated with particular discretion. Other services are local system utilities that may or may not be extraneous. In general, system services should be disabled if not required.

contains 1 rule

#### Disable KDump Kernel Crash Analyzer (kdump) [ref]rule

The `kdump` service provides a kernel crash dump analyzer. It uses the `kexec` system call to boot a secondary kernel ("capture" kernel) following a system crash, which can load information from the crashed kernel for analysis. The `kdump` service can be disabled with the following command:

    $ sudo systemctl disable kdump.service

Rationale:

Kernel core dumps may contain the full contents of system memory at the time of the crash. Kernel core dumps consume a considerable amount of disk space and may result in denial of service by exhausting the available space on the target file system partition. Unless the system is used for kernel development or testing, there is little need to run the kdump service.

Severity: medium

Identifiers: CCE-80258-7

References: AC-17(8), CM-7, CM-6(b), 366, SRG-OS-000480-GPOS-00227, RHEL-07-021230

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

    service_command disable kdump

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Disable service kdump
      service:
        name="{{item}}"
        enabled="no"
        state="stopped"
      with_items:
        - kdump

### Cron and At Daemons [ref]group

The cron and at services are used to allow commands to be executed at a later time. The cron service is required by almost all systems to perform necessary maintenance tasks, while at may or may not be required on a given system. Both daemons should be configured defensively.

contains 3 rules

### Restrict at and cron to Authorized Users if Necessary [ref]group

The `/etc/cron.allow` and `/etc/at.allow` files contain lists of users who are allowed to use `cron` and at to delay execution of processes. If these files exist and if the corresponding files `/etc/cron.deny` and `/etc/at.deny` do not exist, then only users listed in the relevant allow files can run the crontab and `at` commands to submit jobs to be run at scheduled intervals. On many systems, only the system administrator needs the ability to schedule jobs. Note that even if a given user is not listed in `cron.allow`, cron jobs can still be run as that user. The `cron.allow` file controls only administrative access to the crontab command for scheduling and modifying cron jobs.
To restrict `at` and `cron` to only authorized users:

- Remove the `cron.deny` file:

      $ sudo rm /etc/cron.deny

- Edit `/etc/cron.allow`, adding one line for each user allowed to use the crontab command to create cron jobs.
- Remove the `at.deny` file:

      $ sudo rm /etc/at.deny

- Edit `/etc/at.allow`, adding one line for each user allowed to use the at command to create at jobs.

contains 2 rules

#### Verify User Who Owns /etc/cron.allow file [ref]rule

If `/etc/cron.allow` exists, it must be owned by `root`. To properly set the owner of `/etc/cron.allow`, run the command:

    $ sudo chown root /etc/cron.allow

Rationale:

If the owner of the cron.allow file is not set to root, the possibility exists for an unauthorized user to view or edit sensitive information.

Severity: medium

Identifiers: CCE-80378-3

References: AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-021190

#### Verify Group Who Owns /etc/cron.allow file [ref]rule

If `/etc/cron.allow` exists, it must be group-owned by `root`. To properly set the group owner of `/etc/cron.allow`, run the command:

    $ sudo chgrp root /etc/cron.allow

Rationale:

If the owner of the cron.allow file is not set to root, the possibility exists for an unauthorized user to view or edit sensitive information.

Severity: medium

Identifiers: CCE-80379-1

References: AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-021200

#### Enable cron Service [ref]rule

The `crond` service is used to execute commands at preconfigured times. It is required by almost all systems to perform necessary maintenance tasks, such as notifying root of system activity. The `crond` service can be enabled with the following command:

    $ sudo systemctl enable crond.service

Rationale:

Due to its usage for maintenance and security-supporting tasks, enabling the cron daemon is essential.

Severity: medium

Identifiers: CCE-27323-5

References: CM-7, 6.1.2

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

    service_command enable crond

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    - name: Enable service crond
      service:
        name="{{item}}"
        enabled="yes"
        state="started"
      with_items:
        - crond

### SSH Server [ref]group

The SSH protocol is recommended for remote login and remote file transfer. SSH provides confidentiality and integrity for data exchanged between two systems, as well as server authentication, through the use of public key cryptography. The implementation included with the system is called OpenSSH, and more detailed documentation is available from its website, http://www.openssh.org. Its server program is called `sshd` and provided by the RPM package `openssh-server`.

contains 26 rules

### Configure OpenSSH Server if Necessary [ref]group

If the system needs to act as an SSH server, then certain changes should be made to the OpenSSH daemon configuration file `/etc/ssh/sshd_config`. The following recommendations can be applied to this file. See the `sshd_config(5)` man page for more detailed information.

contains 22 rules

#### Enable SSH Server firewalld Firewall exception [ref]rule

By default, inbound connections to SSH's port are allowed. If the SSH server is being used but denied by the firewall, this exception should be added to the firewall configuration.
To configure `firewalld` to allow access, run the following command(s): `firewall-cmd --permanent --add-service=ssh`

Rationale:

If inbound SSH connections are expected, adding a firewall rule exception will allow remote access through the SSH port.

Severity: low

Identifiers: CCE-80361-9

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    sshd_listening_port="22"

    if [ $sshd_listening_port -ne 22] ; then
      firewall-cmd --permanent --add-port=$sshd_listening_port/tcp
    else
      firewall-cmd --permanent --add-service=ssh
    fi

#### Allow Only SSH Protocol 2 [ref]rule

Only SSH protocol version 2 connections should be permitted. The default setting in `/etc/ssh/sshd_config` is correct, and can be verified by ensuring that the following line appears:

    Protocol 2

Rationale:

SSH protocol version 1 is an insecure implementation of the SSH protocol and has many well-known vulnerability exploits. Exploits of the SSH daemon could provide immediate root access to the system.

Severity: high

Identifiers: CCE-27320-1

References: AC-17(8).1(ii), IA-5(1)(c), 197, 366, 6.2.1, SRG-OS-000074-GPOS-00042, SRG-OS-000480-GPOS-00227, RHEL-07-040590

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^Protocol' '2' 'CCE-27320-1' '%s %s'

#### Limit Users' SSH Access [ref]rule

By default, the SSH configuration allows any user with an account to access the system. In order to specify the users that are allowed to login via SSH and deny all other users, add or correct the following line in the `/etc/ssh/sshd_config` file:

    DenyUsers USER1 USER2

Where `USER1` and `USER2` are valid user names. Rationale:

Specifying which accounts are allowed SSH access into the system reduces the possibility of unauthorized access to the system.

Severity: low

Identifiers: CCE-80219-9

References: AC-3

#### Disable GSSAPI Authentication [ref]rule

Unless needed, SSH should not permit extraneous or unnecessary authentication mechanisms like GSSAPI. To disable GSSAPI authentication, add or correct the following line in the `/etc/ssh/sshd_config` file:

    GSSAPIAuthentication no

Rationale:

GSSAPI authentication is used to provide additional authentication mechanisms to applications. Allowing GSSAPI authentication through SSH exposes the system's GSSAPI to remote hosts, increasing the attack surface of the system.

Severity: medium

Identifiers: CCE-80220-7

References: CM-6(c), 368, 318, 1812, 1813, 1814, SRG-OS-000364-GPOS-00151, RHEL-07-040660

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^GSSAPIAuthentication' 'no' 'CCE-80220-7' '%s %s'

#### Disable Kerberos Authentication [ref]rule

Unless needed, SSH should not permit extraneous or unnecessary authentication mechanisms like Kerberos. To disable Kerberos authentication, add or correct the following line in the `/etc/ssh/sshd_config` file:

    KerberosAuthentication no

Rationale:

Kerberos authentication for SSH is often implemented using GSSAPI. If Kerberos is enabled through SSH, the SSH daemon provides a means of access to the system's Kerberos implementation. Vulnerabilities in the system's Kerberos implementations may be subject to exploitation.

Severity: medium

Identifiers: CCE-80221-5

References: CM-6(c), 368, 318, 1812, 1813, 1814, SRG-OS-000364-GPOS-00151, RHEL-07-040670

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^KerberosAuthentication' 'no' 'CCE-80221-5' '%s %s'

#### Enable Use of Strict Mode Checking [ref]rule

SSHs StrictModes option checks file and ownership permissions in the user's home directory `.ssh` folder before accepting login. If world- writable permissions are found, logon is rejected. To enable StrictModes in SSH, add or correct the following line in the `/etc/ssh/sshd_config` file:

    StrictModes yes

Rationale:

If other users have access to modify user-specific SSH configuration files, they may be able to log into the system as another user.

Severity: medium

Identifiers: CCE-80222-3

References: AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040680

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^StrictModes' 'yes' 'CCE-80222-3' '%s %s'

#### Enable Use of Privilege Separation [ref]rule

When enabled, SSH will create an unprivileged child process that has the privilege of the authenticated user. To enable privilege separation in SSH, add or correct the following line in the `/etc/ssh/sshd_config` file:

    UsePrivilegeSeparation yes

Rationale:

SSH daemon privilege separation causes the SSH process to drop root privileges when not needed which would decrease the impact of software vulnerabilities in the unprivileged section.

Severity: medium

Identifiers: CCE-80223-1

References: AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040690

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^UsePrivilegeSeparation' 'yes' 'CCE-80223-1' '%s %s'

#### Disable Compression Or Set Compression to delayed [ref]rule

Compression is useful for slow network connections over long distances but can cause performance issues on local LANs. If use of compression is required, it should be enabled only after a user has authenticated; otherwise , it should be disabled. To disable compression or delay compression until after a user has successfully authenticated, add or correct the following line in the `/etc/ssh/sshd_config` file:

    Compression no

or

    Compression delayed

Rationale:

If compression is allowed in an SSH connection prior to authentication, vulnerabilities in the compression software could result in compromise of the system from an unauthenticated connection, potentially wih root privileges.

Severity: medium

Identifiers: CCE-80224-9

References: CM-6(b), 366, SRG-OS-000480-GPOS-00227, RHEL-07-040700

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^Compression' 'no' 'CCE-80224-9' '%s %s'

#### Print Last Log [ref]rule

When enabled, SSH will display the date and time of the last successful account logon. To enable LastLog in SSH, add or correct the following line in the `/etc/ssh/sshd_config` file:

    PrintLastLog yes

Rationale:

Providing users feedback on when account accesses last occurred facilitates user recognition and reporting of unauthorized account use.

Severity: low

Identifiers: CCE-80225-6

References: AC-9, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040301

#### Set SSH Idle Timeout Interval [ref]rule

SSH allows administrators to set an idle timeout interval. After this interval has passed, the idle user will be automatically logged out.
To set an idle timeout interval, edit the following line in `/etc/ssh/sshd_config` as follows:

    ClientAliveInterval interval

The timeout interval is given in seconds. To have a timeout of 10 minutes, set interval to 600.
If a shorter timeout has already been set for the login shell, that value will preempt any SSH setting made here. Keep in mind that some processes may stop SSH from correctly detecting that the user is idle. Rationale:

Terminating an idle ssh session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been let unattended.

Severity: low

Identifiers: CCE-27433-2

References: AC-2(5), SA-8(i), AC-12, 1133, 2361, SRG-OS-000163-GPOS-00072, SRG-OS-000279-GPOS-00109, RHEL-07-040190, Req-8.1.8, 6.2.12

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    sshd_idle_timeout_value="600"

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^ClientAliveInterval' $sshd_idle_timeout_value 'CCE-27433-2' '%s %s'

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: "SSHD: Set client alive interval"
      lineinfile:
        create=yes
        dest="/etc/ssh/sshd_config"
        regexp="^ClientAliveInterval"
        line="ClientAliveInterval 600"

#### Set SSH Client Alive Count [ref]rule

To ensure the SSH idle timeout occurs precisely when the `ClientAliveCountMax` is set, edit `/etc/ssh/sshd_config` as follows:

    ClientAliveCountMax 0

Rationale:

This ensures a user login will be terminated as soon as the `ClientAliveCountMax` is reached.

Severity: medium

Identifiers: CCE-27082-7

References: AC-2(5), SA-8, AC-12, 1133, 2361, SRG-OS-000163-GPOS-00072, SRG-OS-000279-GPOS-00109, RHEL-07-040191, 6.2.12

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^ClientAliveCountMax' '0' 'CCE-27082-7' '%s %s'

#### Disable SSH Support for .rhosts Files [ref]rule

SSH can emulate the behavior of the obsolete rsh command in allowing users to enable insecure access to their accounts via `.rhosts` files.
To ensure this behavior is disabled, add or correct the following line in `/etc/ssh/sshd_config`:

    IgnoreRhosts yes

Rationale:

SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts.

Severity: medium

Identifiers: CCE-27377-1

References: AC-3, CM-6(a), 366, 6.2.6, RHEL-07-040334, SRG-OS-000480-GPOS-00227

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^IgnoreRhosts' 'yes' 'CCE-27377-1' '%s %s'

#### Disable SSH Support for User Known Hosts [ref]rule

SSH can allow system users user host-based authentication to connect to systems if a cache of the remote systems public keys are available. This should be disabled.
To ensure this behavior is disabled, add or correct the following line in `/etc/ssh/sshd_config`:

    IgnoreUserKnownHosts yes

Rationale:

Configuring this setting for the SSH daemon provides additional assurance that remove login via SSH will require a password, even in the event of misconfiguration elsewhere.

Severity: medium

Identifiers: CCE-80372-6

References: CM-6(a), 366, RHEL-07-040332, SRG-OS-000480-GPOS-00227

#### Disable SSH Support for Rhosts RSA Authentication [ref]rule

SSH can allow authentication through the obsolete rsh command through the use of the authenticating user's SSH keys. This should be disabled.
To ensure this behavior is disabled, add or correct the following line in `/etc/ssh/sshd_config`:

    RhostsRSAAuthentication no

Rationale:

Configuring this setting for the SSH daemon provides additional assurance that remove login via SSH will require a password, even in the event of misconfiguration elsewhere.

Severity: medium

Identifiers: CCE-80373-4

References: CM-6(a), 366, RHEL-07-040333, SRG-OS-000480-GPOS-00227

#### Disable Host-Based Authentication [ref]rule

SSH's cryptographic host-based authentication is more secure than `.rhosts` authentication. However, it is not recommended that hosts unilaterally trust one another, even within an organization.
To disable host-based authentication, add or correct the following line in `/etc/ssh/sshd_config`:

    HostbasedAuthentication no

Rationale:

SSH trust relationships mean a compromise on one host can allow an attacker to move trivially to other hosts.

Severity: medium

Identifiers: CCE-27413-4

References: AC-3, CM-6(b), 366, SRG-OS-000480-GPOS-00229, RHEL-07-010442, 6.2.7

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    grep -q ^HostbasedAuthentication /etc/ssh/sshd_config && \
      sed -i "s/HostbasedAuthentication.*/HostbasedAuthentication no/g" /etc/ssh/sshd_config
    if ! [ $? -eq 0 ]; then
        echo "HostbasedAuthentication no" >> /etc/ssh/sshd_config
    fi

#### Enable Encrypted X11 Fordwarding [ref]rule

By default, remote X11 connections are not encrypted when initiated by users. SSH has the capability to encrypt remote X11 connections when SSH's `X11Forwarding` option is enabled.
To enable X11 Forwarding, add or correct the following line in `/etc/ssh/sshd_config`:

    X11Forwarding yes

Rationale:

Open X displays allow an attacker to capture keystrokes and to execute commands remotely.

Severity: high

Identifiers: CCE-80226-4

References: CM-2(1)(b), 366, SRG-OS-000480-GPOS-00227, RHEL-07-040540

#### Disable SSH Root Login [ref]rule

The root user should never be allowed to login to a system directly over a network. To disable root login via SSH, add or correct the following line in `/etc/ssh/sshd_config`:

    PermitRootLogin no

Rationale:

Even though the communications channel may be encrypted, an additional layer of security is gained by extending the policy of not logging directly on as root. In addition, logging in with a user-specific account provides individual accountability of actions performed on the system and also helps to minimize direct attack attempts on root's password.

Severity: medium

Identifiers: CCE-27445-6

References: AC-3, AC-6(2), IA-2(1), IA-2(5), 366, SRG-OS-000480-GPOS-00227, RHEL-07-040310, 6.2.8

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    SSHD_CONFIG='/etc/ssh/sshd_config'

    # Obtain line number of first uncommented case-insensitive occurrence of Match
    # block directive (possibly prefixed with whitespace) present in $SSHD_CONFIG
    FIRST_MATCH_BLOCK=$(sed -n '/^[[:space:]]*Match[^\n]*/I{=;q}' $SSHD_CONFIG)

    # Obtain line number of first uncommented case-insensitive occurence of
    # PermitRootLogin directive (possibly prefixed with whitespace) present in
    # $SSHD_CONFIG
    FIRST_PERMIT_ROOT_LOGIN=$(sed -n '/^[[:space:]]*PermitRootLogin[^\n]*/I{=;q}' $SSHD_CONFIG)

    # Case: Match block directive not present in $SSHD_CONFIG
    if [ -z "$FIRST_MATCH_BLOCK" ]
    then

        # Case: PermitRootLogin directive not present in $SSHD_CONFIG yet
        if [ -z "$FIRST_PERMIT_ROOT_LOGIN" ]
        then
            # Append 'PermitRootLogin no' at the end of $SSHD_CONFIG
            echo -e "\nPermitRootLogin no" >> $SSHD_CONFIG

        # Case: PermitRootLogin directive present in $SSHD_CONFIG already
        else
            # Replace first uncommented case-insensitive occurrence
            # of PermitRootLogin directive
            sed -i "$FIRST_PERMIT_ROOT_LOGIN s/^[[:space:]]*PermitRootLogin.*$/PermitRootLogin no/I" $SSHD_CONFIG
        fi

    # Case: Match block directive present in $SSHD_CONFIG
    else

        # Case: PermitRootLogin directive not present in $SSHD_CONFIG yet
        if [ -z "$FIRST_PERMIT_ROOT_LOGIN" ]
        then
            # Prepend 'PermitRootLogin no' before first uncommented
            # case-insensitive occurrence of Match block directive
            sed -i "$FIRST_MATCH_BLOCK s/^\([[:space:]]*Match[^\n]*\)/PermitRootLogin no\n\1/I" $SSHD_CONFIG

        # Case: PermitRootLogin directive present in $SSHD_CONFIG and placed
        #       before first Match block directive
        elif [ "$FIRST_PERMIT_ROOT_LOGIN" -lt "$FIRST_MATCH_BLOCK" ]
        then
            # Replace first uncommented case-insensitive occurrence
            # of PermitRootLogin directive
            sed -i "$FIRST_PERMIT_ROOT_LOGIN s/^[[:space:]]*PermitRootLogin.*$/PermitRootLogin no/I" $SSHD_CONFIG

        # Case: PermitRootLogin directive present in $SSHD_CONFIG and placed
        # after first Match block directive
        else
             # Prepend 'PermitRootLogin no' before first uncommented
             # case-insensitive occurrence of Match block directive
             sed -i "$FIRST_MATCH_BLOCK s/^\([[:space:]]*Match[^\n]*\)/PermitRootLogin no\n\1/I" $SSHD_CONFIG
        fi
    fi

#### Disable SSH Access via Empty Passwords [ref]rule

To explicitly disallow SSH login from accounts with empty passwords, add or correct the following line in `/etc/ssh/sshd_config`:

    PermitEmptyPasswords no

Any accounts with empty passwords should be disabled immediately, and PAM configuration should prevent users from being able to assign themselves empty passwords. Rationale:

Configuring this setting for the SSH daemon provides additional assurance that remote login via SSH will require a password, even in the event of misconfiguration elsewhere.

Severity: high

Identifiers: CCE-27471-2

References: AC-3, AC-6, CM-6(b), 366, SRG-OS-000480-GPOS-00229, RHEL-07-010270

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^PermitEmptyPasswords' 'no' 'CCE-27471-2' '%s %s'

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: "SSHD: Disable empty passwords"
      lineinfile:
        create=yes
        dest="/etc/ssh/sshd_config"
        regexp="^PermitEmptyPasswords"
        line="PermitEmptyPasswords no"

#### Enable SSH Warning Banner [ref]rule

To enable the warning banner and ensure it is consistent across the system, add or correct the following line in `/etc/ssh/sshd_config`:

    Banner /etc/issue

Another section contains information on how to create an appropriate system-wide warning banner. Rationale:

The warning message reinforces policy awareness during the logon process and facilitates possible legal action against attackers. Alternatively, systems whose ownership should not be obvious should ensure usage of a banner that does not provide easy attribution.

Severity: medium

Identifiers: CCE-27314-4

References: AC-8(a), AC-8(b), AC-8(c)(1), AC-8(c)(2), AC-8(c)(3), 48, 50, 1384, 1385, 1386, 1387, 1388, SRG-OS-000023-GPOS-00006, SRG-OS-000024-GPOS-00007, SRG-OS-000228-GPOS-00088, 6.2.14, RHEL-07-040170

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^Banner' '/etc/issue' 'CCE-27314-4' '%s %s'

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: "SSHD: Enable warning banner"
      lineinfile:
        create=yes
        dest="/etc/ssh/sshd_config"
        regexp="^Banner"
        line="Banner /etc/issue"

#### Do Not Allow SSH Environment Options [ref]rule

To ensure users are not able to override environment options to the SSH daemon, add or correct the following line in `/etc/ssh/sshd_config`:

    PermitUserEnvironment no

Rationale:

SSH environment options potentially allow users to bypass access restriction in some configurations.

Severity: medium

Identifiers: CCE-27363-1

References: CM-6(b), 366, SRG-OS-000480-GPOS-00229, RHEL-07-010441, 6.2.10

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^PermitUserEnvironment' 'no' 'CCE-27363-1' '%s %s'

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: "SSHD: Do not permit user environment"
      lineinfile:
        create=yes
        dest="/etc/ssh/sshd_config"
        regexp="^PermitUserEnvironment"
        line="PermitUserEnvironment no"

#### Use Only Approved Ciphers [ref]rule

Limit the ciphers to those algorithms which are FIPS-approved. Counter (CTR) mode is also preferred over cipher-block chaining (CBC) mode. The following line in `/etc/ssh/sshd_config` demonstrates use of FIPS-approved ciphers:

    Ciphers aes128-ctr,aes192-ctr,aes256-ctr

The man page `sshd_config(5)` contains a list of supported ciphers. Rationale:

Unapproved mechanisms that are used for authentication to the cryptographic module are not verified and therefore cannot be relied upon to provide confidentiality or integrity, and system data may be compromised.
Operating systems utilizing encryption are required to use FIPS-compliant mechanisms for authenticating to cryptographic modules.
FIPS 140-2 is the current standard for validating that mechanisms used to access cryptographic modules utilize authentication that meets industry and government requirements. For government systems, this allows Security Levels 1, 2, 3, or 4 for use on Red Hat Enterprise Linux.

Severity: medium

Identifiers: CCE-27295-5

References: AC-3, AC-17(2), AU-10(5), CM-6(b), IA-5(1)(c), IA-7, 68, 366, 803, SRG-OS-000033-GPOS-00014, SRG-OS-000120-GPOS-00061, SRG-OS-000125-GPOS-00065, SRG-OS-000250-GPOS-00093, SRG-OS-000393-GPOS-00173, RHEL-07-040110, 6.2.11

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^Ciphers' 'aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc' 'CCE-27295-5' '%s %s'

#### Use Only FIPS Approved MACs [ref]rule

Limit the MACs to those hash algorithms which are FIPS-approved. The following line in `/etc/ssh/sshd_config` demonstrates use of FIPS-approved MACs:

    MACs hmac-sha2-512,hmac-sha2-256

Rationale:

DoD Information Systems are required to use FIPS-approved cryptographic hash functions. The only SSHv2 hash algorithms meeting this requirement is SHA2.

Severity: medium

Identifiers: CCE-27455-5

References: AC-17(2), IA-7, SC-13, 1453, SRG-OS-000250-GPOS-00093, RHEL-07-040620

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function replace_or_append {
      local config_file=$1
      local key=$2
      local value=$3
      local cce=$4
      local format=$5

      # Check sanity of the input
      if [ $# -lt "3" ]
      then
            echo "Usage: replace_or_append 'config_file_location' 'key_to_search' 'new_value'"
            echo
            echo "If symlinks need to be taken into account, add yes/no to the last argument"
            echo "to allow to 'follow_symlinks'."
            echo "Aborting."
            exit 1
      fi

      # Test if the config_file is a symbolic link. If so, use --follow-symlinks with sed.
      # Otherwise, regular sed command will do.
      if test -L $config_file; then
        sed_command="sed -i --follow-symlinks"
      else
        sed_command="sed -i"
      fi

      # Test that the cce arg is not empty or does not equal $CCENUM.
      # If $CCENUM exists, it means that there is no CCE assigned.
      if ! [ "x$cce" = x ] && [ "$cce" != '$CCENUM' ]; then
        cce="CCE-${cce}"
      else
        cce="CCE"
      fi

      # Strip any search characters in the key arg so that the key can be replaced without
      # adding any search characters to the config file.
      stripped_key=$(sed "s/[\^=\$,;+]*//g" <<< $key)

      # If there is no print format specified in the last arg, use the default format.
      if ! [ "x$format" = x ] ; then
        printf -v formatted_output "$format" $stripped_key $value
      else
        formatted_output="$stripped_key = $value"
      fi

      # If the key exists, change it. Otherwise, add it to the config_file.
      if `grep -qi $key $config_file` ; then
        $sed_command "s/$key.*/$formatted_output/g" $config_file
      else
        echo -ne "\n# Per $cce: Set $formatted_output in $config_file" >> $config_file
        echo -ne "\n$formatted_output" >> $config_file
      fi

    }

    replace_or_append '/etc/ssh/sshd_config' '^MACs' 'hmac-sha2-512,hmac-sha2-256,hmac-sha1' 'CCE-27455-5' '%s %s'

#### Install the OpenSSH Server Package [ref]rule

The `openssh-server` package should be installed. The `openssh-server` package can be installed with the following command:

    $ sudo yum install openssh-server

Rationale:

Without protection of the transmitted information, confidentiality, and integrity may be compromised because unprotected communications can be intercepted and either read or altered.

Severity: medium

Identifiers: CCE-80215-7

References: SC-8, 2418, 2420, 2421, 2422, SRG-OS-000423-GPOS-00187, SRG-OS-000423-GPOS-00188, SRG-OS-000423-GPOS-00189, SRG-OS000423-GPOS-00190, RHEL-07-040260

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command install openssh-server

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    - name: Ensure openssh-server is installed
      package:
        name="{{item}}"
        state=present
      with_items:
        - openssh-server

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    include install_openssh-server

    class install_openssh-server {
      package { 'openssh-server':
        ensure => 'installed',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | enable

    package --add=openssh-server

#### Enable the OpenSSH Service [ref]rule

The SSH server service, sshd, is commonly needed. The `sshd` service can be enabled with the following command:

    $ sudo systemctl enable sshd.service

Rationale:

Without protection of the transmitted information, confidentiality, and integrity may be compromised because unprotected communications can be intercepted and either read or altered.
This checklist item applies to both internal and external networks and all types of information system components from which information can be transmitted (e.g., servers, mobile devices, notebook computers, printers, copiers, scanners, etc). Communication paths outside the physical protection of a controlled boundary are exposed to the possibility of interception and modification.

Severity: medium

Identifiers: CCE-80216-5

References: SC-8, 2418, 2420, 2421, 2422, SRG-OS-000423-GPOS-00187, SRG-OS-000423-GPOS-00188, SRG-OS-000423-GPOS-00189, SRG-OS000423-GPOS-00190, RHEL-07-040261

#### Verify Permissions on SSH Server Public *.pub Key Files [ref]rule

To properly set the permissions of `/etc/ssh/*.pub`, run the command:

    $ sudo chmod 0644 /etc/ssh/*.pub

Rationale:

If a public host key file is modified by an unauthorized user, the SSH service may be compromised.

Severity: medium

Identifiers: CCE-27311-0

References: AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040640

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    chmod 0644 /etc/ssh/*.pub

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include ssh_public_key_perms

    class ssh_public_key_perms {
      exec { 'sshd_pub_key':
        command => "chmod 0644 /etc/ssh/*.pub",
        path    => '/bin:/usr/bin'
      }
    }

#### Verify Permissions on SSH Server Private *_key Key Files [ref]rule

To properly set the permissions of `/etc/ssh/*_key`, run the command:

    $ sudo chmod 0640 /etc/ssh/*_key

Rationale:

If an unauthorized user obtains the private SSH host key file, the host could be impersonated.

Severity: medium

Identifiers: CCE-27485-2

References: AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040650

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    chmod 0640 /etc/ssh/*_key

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include ssh_private_key_perms

    class ssh_private_key_perms {
      exec { 'sshd_priv_key':
        command => "chmod 0640 /etc/ssh/*_key",
        path    => '/bin:/usr/bin'
      }
    }

### System Security Services Daemon [ref]group

The System Security Services Daemon (SSSD) is a system daemon that provides access to different identity and authentication providers such as Red Hat's IdM, Microsoft's AD, openLDAP, MIT Kerberos, etc. It uses a common framework that can provide caching and offline support to systems utilizing SSSD. SSSD using caching to reduce load on authentication servers permit offline authentication as well as store extended user user data.
For more information, see https://access.redhat.com/documentation/en_US/Red_Hat_Enterprise_Linux/7/html/System-Level_Authentication_Guide/SSSD.html

contains 3 rules

#### Configure SSSD's Memory Cache to Expire [ref]rule

SSSD's memory cache should be configured to set to expire records after 1 day. To configure SSSD to expire memory cache, set `memcache_timeout` to `86400` under the `[nss]` section in `/etc/sssd/sssd.conf`. For example:

    [nss]
    memcache_timeout = 86400

Rationale:

If cached authentication information is out-of-date, the validity of the authentication information may be questionable.

Severity: medium

Identifiers: CCE-80364-3

References: IA-5(13), 2007, SRG-OS-000383-GPOS-00166, RHEL-07-010400

#### Configure SSSD to Expire Offline Credentials [ref]rule

SSSD should be configured to expire offline credentials after 1 day. To configure SSSD to expire offline credentials, set `offline_credentials_expiration` to `1` under the `[pam]` section in `/etc/sssd/sssd.conf`. For example:

    [pam]
    offline_credentials_expiration = 1

Rationale:

If cached authentication information is out-of-date, the validity of the authentication information may be questionable.

Severity: medium

Identifiers: CCE-80365-0

References: IA-5(13), 2007, SRG-OS-000383-GPOS-00166, RHEL-07-010401

#### Configure SSSD to Expire SSH Known Hosts [ref]rule

SSSD should be configured to expire keys from known SSH hosts after 1 day. To configure SSSD to known SSH hosts, set `ssh_known_hosts_timeout` to `86400` under the `[ssh]` section in `/etc/sssd/sssd.conf`. For example:

    [ssh]
    ssh_known_hosts_timeout = 86400

Rationale:

If cached authentication information is out-of-date, the validity of the authentication information may be questionable.

Severity: medium

Identifiers: CCE-80366-8

References: IA-5(13), 2007, SRG-OS-000383-GPOS-00166, RHEL-07-010402, IA-5(13), 2007

### Network Time Protocol [ref]group

The Network Time Protocol is used to manage the system clock over a network. Computer clocks are not very accurate, so time will drift unpredictably on unmanaged systems. Central time protocols can be used both to ensure that time is consistent among a network of machines, and that their time is consistent with the outside world.
If every system on a network reliably reports the same time, then it is much easier to correlate log messages in case of an attack. In addition, a number of cryptographic protocols (such as Kerberos) use timestamps to prevent certain types of attacks. If your network does not have synchronized time, these protocols may be unreliable or even unusable.
Depending on the specifics of the network, global time accuracy may be just as important as local synchronization, or not very important at all. If your network is connected to the Internet, using a public timeserver (or one provided by your enterprise) provides globally accurate timestamps which may be essential in investigating or responding to an attack which originated outside of your network.
A typical network setup involves a small number of internal systems operating as NTP servers, and the remainder obtaining time information from those internal servers.
There is a choice between the daemons `ntpd` and `chronyd`, which are available from the repositories in the `ntp` and `chrony` packages respectively.
The default `chronyd` daemon can work well when external time references are only intermittently accesible, can perform well even when the network is congested for longer periods of time, can usually synchronize the clock faster and with better time accuracy, and quickly adapts to sudden changes in the rate of the clock, for example, due to changes in the temperature of the crystal oscillator. `Chronyd` should be considered for all systems which are frequently suspended or otherwise intermittently disconnected and reconnected to a network. Mobile and virtual systems for example.
The `ntpd` NTP daemon fully supports NTP protocol version 4 (RFC 5905), including broadcast, multicast, manycast clients and servers, and the orphan mode. It also supports extra authentication schemes based on public-key cryptography (RFC 5906). The NTP daemon (`ntpd`) should be considered for systems which are normally kept permanently on. Systems which are required to use broadcast or multicast IP, or to perform authentication of packets with the `Autokey` protocol, should consider using `ntpd`.
Refer to https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/ch-Configuring_NTP_Using_the_chrony_Suite.html for more detailed comparison of features of `chronyd` and `ntpd` daemon features respectively, and for further guidance how to choose between the two NTP daemons.
The upstream manual pages at http://chrony.tuxfamily.org/manual.html for `chronyd` and http://www.ntp.org for `ntpd` provide additional information on the capabilities and configuration of each of the NTP daemons.

contains 3 rules

#### Enable the NTP Daemon [ref]rule

The `chronyd` service can be enabled with the following command:

    $ sudo systemctl enable chronyd.service

Note: The `chronyd` daemon is enabled by default.
The `ntpd` service can be enabled with the following command:

    $ sudo systemctl enable ntpd.service

Note: The `ntpd` daemon is not enabled by default. Though as mentioned in the previous sections in certain environments the `ntpd` daemon might be preferred to be used rather than the `chronyd` one. Refer to: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/ch-Configuring_NTP_Using_the_chrony_Suite.html for guidance which NTP daemon to choose depending on the environment used. Rationale:

Enabling some of `chronyd` or `ntpd` services ensures that the NTP daemon will be running and that the system will synchronize its time to any servers specified. This is important whether the system is configured to be a client (and synchronize only its own clock) or it is also acting as an NTP server to other systems. Synchronizing time is essential for authentication services such as Kerberos, but it is also important for maintaining accurate logs and auditing possible security breaches.
The `chronyd` and `ntpd` NTP daemons offer all of the functionality of `ntpdate`, which is now deprecated. Additional information on this is available at http://support.ntp.org/bin/view/Dev/DeprecatingNtpdate

Severity: medium

Identifiers: CCE-27444-9

References: AU-8(1), 160, Req-10.4, 3.6

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    if ! `rpm -q --quiet chrony` && ! `rpm -q --quiet ntp-`; then

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

      package_command install chrony
      service_command enable chronyd
    elif `rpm -q --quiet chrony`; then
      if ! [ `/usr/sbin/pidof ntpd` ] ; then

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

        service_command enable chronyd
      fi
    else

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

      service_command enable ntpd
    fi

#### Specify a Remote NTP Server [ref]rule

Depending on specific functional requirements of a concrete production environment, the Red Hat Enterprise Linux 7 Server system can be configured to utilize the services of the `chronyd` NTP daemon (the default), or services of the `ntpd` NTP daemon. Refer to https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/ch-Configuring_NTP_Using_the_chrony_Suite.html for more detailed comparison of the features of both of the choices, and for further guidance how to choose between the two NTP daemons.
To specify a remote NTP server for time synchronization, perform the following:

- if the system is configured to use the `chronyd` as the NTP daemon (the default), edit the file `/etc/chrony.conf` as follows,
- if the system is configured to use the `ntpd` as the NTP daemon, edit the file `/etc/ntp.conf` as documented below.

Add or correct the following lines, substituting the IP or hostname of a remote NTP server for ntpserver:

    server ntpserver

This instructs the NTP software to contact that remote server to obtain time data. Rationale:

Synchronizing with an NTP server makes it possible to collate system logs from multiple sources or correlate computer events with real time events.

Severity: medium

Identifiers: CCE-27278-1

References: AU-8(1), 160, Req-10.4.1, Req-10.4.3, 3.6

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_multiple_time_servers="0.rhel.pool.ntp.org,1.rhel.pool.ntp.org,2.rhel.pool.ntp.org,3.rhel.pool.ntp.org"

    if ! `/usr/sbin/pidof ntpd`; then
      if ! `grep -q ^server /etc/chrony.conf` ; then
        if ! `grep -q '#[[:space:]]*server' /etc/chrony.conf` ; then
          for i in `echo "$var_multiple_time_servers" | tr ',' '\n'` ; do
            echo -ne "\nserver $i iburst" >> /etc/chrony.conf
          done
        else
          sed -i 's/#[ ]*server/server/g' /etc/chrony.conf
        fi
      fi
    else
      if ! `grep -q ^server /etc/ntp.conf` ; then
        if ! `grep -q '#[[:space:]]*server' /etc/ntp.conf` ; then
          for i in `echo "$var_multiple_time_servers" | tr ',' '\n'` ; do
            echo -ne "\nserver $i iburst" >> /etc/ntp.conf
          done
        else
          sed -i 's/#[ ]*server/server/g' /etc/ntp.conf
        fi
      fi
    fi

#### Specify Additional Remote NTP Servers [ref]rule

Depending on specific functional requirements of a concrete production environment, the Red Hat Enterprise Linux 7 Server system can be configured to utilize the services of the `chronyd` NTP daemon (the default), or services of the `ntpd` NTP daemon. Refer to https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/ch-Configuring_NTP_Using_the_chrony_Suite.html for more detailed comparison of the features of both of the choices, and for further guidance how to choose between the two NTP daemons.
Additional NTP servers can be specified for time synchronization. To do so, perform the following:

- if the system is configured to use the `chronyd` as the NTP daemon (the default), edit the file `/etc/chrony.conf` as follows,
- if the system is configured to use the `ntpd` as the NTP daemon, edit the file `/etc/ntp.conf` as documented below.

Add additional lines of the following form, substituting the IP address or hostname of a remote NTP server for ntpserver:

    server ntpserver

Rationale:

Specifying additional NTP servers increases the availability of accurate time data, in the event that one of the specified servers becomes unavailable. This is typical for a system acting as an NTP server for other systems.

Severity: low

Identifiers: CCE-27012-4

References: AU-8(1), Req-10.4.3

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    var_multiple_time_servers="0.rhel.pool.ntp.org,1.rhel.pool.ntp.org,2.rhel.pool.ntp.org,3.rhel.pool.ntp.org"

    if ! `/usr/sbin/pidof ntpd`; then
      if [ `grep -c '^server' /etc/chrony.conf` -lt 2 ]; then
        if ! `grep -q '#[[:space:]]*server' /etc/chrony.conf` ; then
          for i in `echo "$var_multiple_time_servers" | tr ',' '\n'` ; do
            echo -ne "\nserver $i iburst" >> /etc/chrony.conf
          done
        else
          sed -i 's/#[ ]*server/server/g' /etc/chrony.conf
        fi
      fi
    else
      if [ `grep -c '^server' /etc/ntp.conf` -lt 2 ]; then
        if ! `grep -q '#[[:space:]]*server' /etc/ntp.conf` ; then
          for i in `echo "$var_multiple_time_servers" | tr ',' '\n'` ; do
            echo -ne "\nserver $i iburst" >> /etc/ntp.conf
          done
        else
          sed -i 's/#[ ]*server/server/g' /etc/ntp.conf
        fi
      fi
    fi

### LDAP [ref]group

LDAP is a popular directory service, that is, a standardized way of looking up information from a central database. Red Hat Enterprise Linux 7 includes software that enables a system to act as both an LDAP client and server.

contains 1 rule

### Configure OpenLDAP Clients [ref]group

This section provides information on which security settings are important to configure in OpenLDAP clients by manually editing the appropriate configuration files. Red Hat Enterprise Linux 7 provides an automated configuration tool called authconfig and a graphical wrapper for authconfig called `system-config-authentication`. However, these tools do not provide as much control over configuration as manual editing of configuration files. The authconfig tools do not allow you to specify locations of SSL certificate files, which is useful when trying to use SSL cleanly across several protocols. Installation and configuration of OpenLDAP on Red Hat Enterprise Linux 7 is available at https://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/ch-Directory_Servers.html.

Warning: Before configuring any system to be an LDAP client, ensure that a working LDAP server is present on the network.

contains 1 rule

#### Configure LDAP Client to Use TLS For All Transactions [ref]rule

This check verifies that RHEL7 impliments cryptography to protect the integrity of remote LDAP authentication sessions.
To determine if LDAP is being used for authentication, use the following command:

    $ sudo grep -i useldapauth /etc/sysconfig/authconfig

If `USELDAPAUTH=yes`, then LDAP is being used. To check if LDAP is configured to use TLS, use the following command:

    $ sudo grep -i ssl /etc/pam_ldap.conf

Rationale:

Without cryptographic integrity protections, information can be altered by unauthorized users without detection. The ssl directive specifies whether to use TLS or not. If not specified it will default to no. It should be set to start_tls rather than doing LDAP over SSL.

Severity: medium

Identifiers: CCE-80291-8

References: AC-17(2), CM-7, 1453, SRG-OS-000250-GPOS-00093, RHEL-07-040180

### NFS and RPC [ref]group

The Network File System is a popular distributed filesystem for the Unix environment, and is very widely deployed. This section discusses the circumstances under which it is possible to disable NFS and its dependencies, and then details steps which should be taken to secure NFS's configuration. This section is relevant to machines operating as NFS clients, as well as to those operating as NFS servers.

contains 4 rules

### Configure NFS Clients [ref]group

The steps in this section are appropriate for machines which operate as NFS clients.

contains 3 rules

### Mount Remote Filesystems with Restrictive Options [ref]group

Edit the file `/etc/fstab`. For each filesystem whose type (column 3) is `nfs` or `nfs4`, add the text `,nodev,nosuid` to the list of mount options in column 4. If appropriate, also add `,noexec`.
See the section titled "Restrict Partition Mount Options" for a description of the effects of these options. In general, execution of files mounted via NFS should be considered risky because of the possibility that an adversary could intercept the request and substitute a malicious file. Allowing setuid files to be executed from remote servers is particularly risky, both for this reason and because it requires the clients to extend root-level trust to the NFS server.

contains 3 rules

#### Mount Remote Filesystems with nodev [ref]rule

Add the `nodev` option to the fourth column of `/etc/fstab` for the line which controls mounting of any NFS mounts.

Rationale:

Legitimate device files should only exist in the /dev directory. NFS mounts should not present device files to users.

Severity: medium

Identifiers: CCE-80239-7

References: CM-7, MP-2

#### Mount Remote Filesystems with nosuid [ref]rule

Add the `nosuid` option to the fourth column of `/etc/fstab` for the line which controls mounting of any NFS mounts.

Rationale:

NFS mounts should not present suid binaries to users. Only vendor-supplied suid executables should be installed to their default location on the local filesystem.

Severity: medium

Identifiers: CCE-80240-5

References: AC-6, 366, SRG-OS-000480-GPOS-00227, RHEL-07-021012

#### Mount Remote Filesystems with Kerberos Security [ref]rule

Add the `sec=krb5:krb5i:krb5p` option to the fourth column of `/etc/fstab` for the line which controls mounting of any NFS mounts.

Rationale:

When an NFS server is configured to use AUTH_SYS a selected userid and groupid are used to handle requests from the remote user. The userid and groupid could mistakenly or maliciously be set incorrectly. The AUTH_GSS method of authentication uses certificates on the server and client systems to more securely authenticate the remote mount request.

Severity: medium

Identifiers: CCE-27458-9

References: AC-14(1), 366, SRG-OS-000480-GPOS-00227, RHEL-07-040740

### Configure NFS Servers [ref]group

The steps in this section are appropriate for machines which operate as NFS servers.

contains 1 rule

#### Use Kerberos Security on All Exports [ref]rule

Using Kerberos on all exported mounts prevents a malicious client or user from impersonating a system user. To cryptography authenticate users to the NFS server, add `sec=krb5:krb5i:krb5p` to each export in `/etc/exports`.

Rationale:

When an NFS server is configured to use AUTH_SYS a selected userid and groupid are used to handle requests from the remote user. The userid and groupid could mistakenly or maliciously be set incorrectly. The AUTH_GSS method of authentication uses certificates on the server and client systems to more securely authenticate the remote mount request.

Severity: medium

Identifiers: CCE-27464-7

References: AC-14(1), 366, SRG-OS-000480-GPOS-00227, RHEL-07-040740

### FTP Server [ref]group

FTP is a common method for allowing remote access to files. Like telnet, the FTP protocol is unencrypted, which means that passwords and other data transmitted during the session can be captured and that the session is vulnerable to hijacking. Therefore, running the FTP server software is not recommended.
However, there are some FTP server configurations which may be appropriate for some environments, particularly those which allow only read-only anonymous access as a means of downloading data available to the public.

contains 2 rules

### Disable vsftpd if Possible [ref]group

To minimize attack surface, disable vsftpd if at all possible.

contains 1 rule

#### Uninstall vsftpd Package [ref]rule

The `vsftpd` package can be removed with the following command:

    $ sudo yum erase vsftpd

Rationale:

Removing the vsftpd package decreases the risk of its accidental activation.

Severity: high

Identifiers: CCE-80245-4

References: CM-6(b), CM-7, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040490, 3.10

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function package_command {

    # Load function arguments into local variables
    local package_operation=$1
    local package=$2

    # Check sanity of the input
    if [ $# -ne "2" ]
    then
      echo "Usage: package_command 'install/uninstall' 'rpm_package_name"
      echo "Aborting."
      exit 1
    fi

    # If dnf is installed, use dnf; otherwise, use yum
    if [ -f "/usr/bin/dnf" ] ; then
      install_util="/usr/bin/dnf"
    else
      install_util="/usr/bin/yum"
    fi

    if [ "$package_operation" != 'remove' ] ; then
      # If the rpm is not installed, install the rpm
      if ! /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    else
      # If the rpm is installed, uninstall the rpm
      if /bin/rpm -q --quiet $package; then
        $install_util -y $package_operation $package
      fi
    fi

    }

    package_command remove vsftpd

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Ensure vsftpd is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - vsftpd

Remediation Puppet snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    include remove_vsftpd

    class remove_vsftpd {
      package { 'vsftpd':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    package -remove=vsftpd

### Use vsftpd to Provide FTP Service if Necessary [ref]group

The primary vsftpd configuration file is `/etc/vsftpd.conf`, if that file exists, or `/etc/vsftpd/vsftpd.conf` if it does not.

contains 1 rule

#### Create Warning Banners for All FTP Users [ref]rule

Edit the vsftpd configuration file, which resides at `/etc/vsftpd/vsftpd.conf` by default. Add or correct the following configuration options:

    banner_file=/etc/issue

Rationale:

This setting will cause the system greeting banner to be used for FTP connections as well.

Severity: medium

Identifiers: CCE-80248-8

References: 48

### Network Routing [ref]group

A router is a very desirable target for a potential adversary because they fulfill a variety of infrastructure networking roles such as access to network segments, gateways to other networks, filtering, etc. Therefore, if one is required, the machine acting as a router should be dedicated to that purpose alone and be stored in a physically secure location. The system's default routing software is Quagga, and provided in an RPM package of the same name.

contains 1 rule

### Disable Quagga if Possible [ref]group

If Quagga was installed and activated, but the system does not need to act as a router, then it should be disabled and removed.

contains 1 rule

#### Disable Quagga Service [ref]rule

The `zebra` service can be disabled with the following command:

    $ sudo systemctl disable zebra.service

Rationale:

Routing protocol daemons are typically used on routers to exchange network topology information with other routers. If routing daemons are used when not required, system network information may be unnecessarily transmitted across the network.

Severity: medium

Identifiers: CCE-27191-6

References: SC-32, 366, SRG-OS-000480-GPOS-00227, RHEL-07-040730

Remediation Shell script: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    function service_command {

    # Load function arguments into local variables
    local service_state=$1
    local service=$2
    local xinetd=$(echo $3 | cut -d'=' -f2)

    # Check sanity of the input
    if [ $# -lt "2" ]
    then
      echo "Usage: service_command 'enable/disable' 'service_name.service'"
      echo
      echo "To enable or disable xinetd services add \'xinetd=service_name\'"
      echo "as the last argument"
      echo "Aborting."
      exit 1
    fi

    # If systemctl is installed, use systemctl command; otherwise, use the service/chkconfig commands
    if [ -f "/usr/bin/systemctl" ] ; then
      service_util="/usr/bin/systemctl"
    else
      service_util="/sbin/service"
      chkconfig_util="/sbin/chkconfig"
    fi

    # If disable is not specified in arg1, set variables to enable services.
    # Otherwise, variables are to be set to disable services.
    if [ "$service_state" != 'disable' ] ; then
      service_state="enable"
      service_operation="start"
      chkconfig_state="on"
    else
      service_state="disable"
      service_operation="stop"
      chkconfig_state="off"
    fi

    # If chkconfig_util is not empty, use chkconfig/service commands.
    if ! [ "x$chkconfig_util" = x ] ; then
      $service_util $service $service_operation
      $chkconfig_util --level 0123456 $service $chkconfig_state
    else
      $service_util $service_operation $service
      $service_util $service_state $service
    fi

    # Test if local variable xinetd is empty using non-bashism.
    # If empty, then xinetd is not being used.
    if ! [ "x$xinetd" = x ] ; then
      grep -qi disable /etc/xinetd.d/$xinetd && \

      if ! [ "$service_operation" != 'disable' ] ; then
        sed -i "s/disable.*/disable         = no/gI" /etc/xinetd.d/$xinetd
      else
        sed -i "s/disable.*/disable         = yes/gI" /etc/xinetd.d/$xinetd
      fi
    fi

    }

    service_command disable zebra

Remediation Ansible snippet: (show)

Complexity: | low
Disruption: | low
Reboot: | false
Strategy: | disable

    - name: Disable service zebra
      service:
        name="{{item}}"
        enabled="no"
        state="stopped"
      with_items:
        - zebra

### SNMP Server [ref]group

The Simple Network Management Protocol allows administrators to monitor the state of network devices, including computers. Older versions of SNMP were well-known for weak security, such as plaintext transmission of the community string (used for authentication) and usage of easily-guessable choices for the community string.

contains 1 rule

### Configure SNMP Server if Necessary [ref]group

If it is necessary to run the snmpd agent on the system, some best practices should be followed to minimize the security risk from the installation. The multiple security models implemented by SNMP cannot be fully covered here so only the following general configuration advice can be offered:

- use only SNMP version 3 security models and enable the use of authentication and encryption
- write access to the MIB (Management Information Base) should be allowed only if necessary
- all access to the MIB should be restricted following a principle of least privilege
- network access should be limited to the maximum extent possible including restricting to expected network addresses both in the configuration files and in the system firewall rules
- ensure SNMP agents send traps only to, and accept SNMP queries only from, authorized management stations
- ensure that permissions on the `snmpd.conf` configuration file (by default, in `/etc/snmp`) are 640 or more restrictive
- ensure that any MIB files' permissions are also 640 or more restrictive

contains 1 rule

#### Ensure Default SNMP Password Is Not Used [ref]rule

Edit `/etc/snmp/snmpd.conf`, remove or change the default community strings of `public` and `private`. Once the default community strings have been changed, restart the SNMP service:

    $ sudo service snmpd restart

Rationale:

Whether active or not, default simple network management protocol (SNMP) community strings must be changed to maintain security. If the service is running with the default authenticators, then anyone can gather data about the system and the network and use the information to potentially compromise the integrity of the system and network(s).

Severity: high

Identifiers: CCE-27386-2

References: IA-5.1(ii), 366, SRG-OS-000480-GPOS-00227, RHEL-07-040580

Red Hat and Red Hat Enterprise Linux are either registered trademarks or trademarks of Red Hat, Inc. in the United States and other countries. All other names are registered trademarks or trademarks of their respective companies.