## Guide to the Secure Configuration of Red Hat Enterprise Linux 6

> with profile CNSSI 1253 Low/Low/Low Control Baseline for Red Hat Enterprise Linux 6
> This profile follows the Committee on National Security Systems Instruction (CNSSI) No. 1253, "Security Categorization and Control Selection for National Security Systems" on security controls to meet low confidentiality, low integrity, and low assurance."

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 6. 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 6, which provides required settings for US Department of Defense systems, is one example of a baseline created from this guidance.

This benchmark is a direct port of a SCAP Security Guide benchmark developed for Red Hat Enterprise Linux. It has been modified through an automated process to remove specific dependencies on Red Hat Enterprise Linux and to function with Scientifc Linux. The result is a generally useful SCAP Security Guide benchmark with the following caveats:

- Scientifc Linux is not an exact copy of Red Hat Enterprise Linux. Scientific Linux is a Linux distribution produced by Fermi National Accelerator Laboratory. It is a free and open source operating system based on Red Hat Enterprise Linux and aims to be "as close to the commercial enterprise distribution as we can get it." There may be configuration differences that produce false positives and/or false negatives. If this occurs please file a bug report.
- Scientifc Linux is derived from the free and open source software made available by Red Hat, but it is not produced, maintained or supported by Red Hat. Scientifc Linux has its own build system, compiler options, patchsets, and is a community supported, non-commercial operating system. Scientifc Linux does not inherit certifications or evaluations from Red Hat Enterprise Linux. As such, some configuration rules (such as those requiring FIPS 140-2 encryption) will continue to fail on Scientifc Linux.

Members of the Scientifc Linux community are invited to participate in OpenSCAP and SCAP Security Guide development. Bug reports and patches can be sent to GitHub: https://github.com/OpenSCAP/scap-security-guide. The mailing list is at https://fedorahosted.org/mailman/listinfo/scap-security-guide.

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 | CNSSI 1253 Low/Low/Low Control Baseline for Red Hat Enterprise Linux 6
Profile ID | xccdf_org.ssgproject.content_profile_nist-cl-il-al

## Revision History

Current version: 0.1.31

- draft (as of 2017-08-11)

## Platforms

- cpe:/o:redhat:enterprise_linux:6
- cpe:/o:scientificlinux:scientificlinux:6
- cpe:/o:redhat:enterprise_linux:6::client
- cpe:/o:redhat:enterprise_linux:6::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. Avahi Server
6. Print Support
7. DHCP
8. Network Time Protocol
9. Mail Server Software
10. LDAP
11. NFS and RPC
12. DNS Server
13. FTP Server
14. Web Server
15. Samba(SMB) Microsoft Windows File Sharing Server

## Checklist

contains 267 rules

### System Settings [ref]group

Contains rules that check correct system settings.

contains 191 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 21 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

References: SC-32, 1208

#### 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

References: SC-32, 1208

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

System logs are stored in the `/var/log` directory. Ensure that it has its own partition or logical volume at installation time, or migrate it using LVM.

Rationale:

Placing `/var/log` in its own partition enables better separation between log files and other files in `/var/`.

Severity: low

References: AU-9, SC-32, 1208

#### 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

References: AU-4, AU-9, SC-32, 137, 138, 1208

#### 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

References: SC-32, 1208

### 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 4 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:

The Red Hat GPG key is necessary to cryptographically verify packages are from Red Hat.

Severity: high

References: SI-7, MA-1(b), 351

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:

Ensuring the validity of packages' cryptographic signatures prior to installation ensures the authenticity of the software and protects against malicious tampering.

Severity: medium

References: SI-7, MA-1(b), 352, 663

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:

Ensuring all packages' cryptographic signatures are valid prior to installation ensures the authenticity of the software and protects against malicious tampering.

Severity: low

References: SI-7, MA-1(b), 352, 663

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`. Rationale:

Installing software updates is a fundamental mitigation against the exploitation of publicly-known vulnerabilities.

Severity: medium

References: SI-2, MA-1(b), 1227, 1233

Remediation Shell script: (show)

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

    yum -y update

### 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.
Integrity checking cannot prevent intrusions, but can detect that they have occurred. Requirements for software 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 6 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 3 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

References: CM-3(d), CM-3(e), CM-6(d), SC-28, SI-7, 1069

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

References: CM-3(d), CM-3(e), CM-6(d), SC-28, SI-7, 374, 416, 1069, 1263, 1297, 1589

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

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

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.

Severity: medium

References: CM-3(d), CM-3(e), CM-6(d), SC-28, SI-7, 374, 416, 1069, 1263, 1297, 1589

Remediation Shell script: (show)

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

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

### 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

The RPM package management system can check file access permissions of installed software packages, including many that are important to system security. 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 #1277603.
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: low

References: AC-6, CM-6(d), SI-7, 1493, 1494, 1495

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

The RPM package management system can check the hashes of installed software packages, including many that are important to system security. 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: low

References: CM-6(d), SI-7, 1496

#### 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

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

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 6 rules

### Configure GNOME Screen Locking [ref]group

In the default GNOME desktop, the screen can be locked by choosing Lock Screen from the System menu.
The `gconftool-2` program can be used to enforce mandatory screen locking settings for the default GNOME environment. 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 Lock Screen icon from the System menu can also be dragged to the taskbar in order to facilitate even more convenient screen-locking.
The root account cannot be screen-locked, but this should have no practical effect as 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 configuring GNOME screensaver, see http://live.gnome.org/GnomeScreensaver. For more information about enforcing preferences in the GNOME environment using the GConf configuration system, see http://projects.gnome.org/gconf and the man page `gconftool-2(1)`.

contains 4 rules

#### Set GNOME Login Inactivity Timeout [ref]rule

Run the following command to set the idle time-out value for inactivity in the GNOME desktop to 900 minutes:

    $ sudo gconftool-2 \
      --direct \
      --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \
      --type int \
      --set /desktop/gnome/session/idle_delay 900

Rationale:

Setting the idle delay controls when the screensaver will start, and can be combined with screen locking to prevent access from passersby.

Severity: medium

References: AC-11(a), 57

Remediation Shell script: (show)

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

    inactivity_timeout_value="900"

    # Install GConf2 package if not installed
    if ! rpm -q GConf2; then
      yum -y install GConf2
    fi

    # Set the idle time-out value for inactivity in the GNOME desktop to meet the
    # requirement
    gconftool-2 --direct \
                --config-source "xml:readwrite:/etc/gconf/gconf.xml.mandatory" \
                --type int \
                --set /desktop/gnome/session/idle_delay ${inactivity_timeout_value}

#### GNOME Desktop Screensaver Mandatory Use [ref]rule

Run the following command to activate the screensaver in the GNOME desktop after a period of inactivity:

    $ sudo gconftool-2 --direct \
      --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \
      --type bool \
      --set /apps/gnome-screensaver/idle_activation_enabled true

Rationale:

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

References: AC-11(a), 57

Remediation Shell script: (show)

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

    # Install GConf2 package if not installed
    if ! rpm -q GConf2; then
      yum -y install GConf2
    fi

    # Set the screensaver activation in the GNOME desktop after a period of inactivity
    gconftool-2 --direct \
                --config-source "xml:readwrite:/etc/gconf/gconf.xml.mandatory" \
                --type bool \
                --set /apps/gnome-screensaver/idle_activation_enabled true

#### Enable Screen Lock Activation After Idle Period [ref]rule

Run the following command to activate locking of the screensaver in the GNOME desktop when it is activated:

    $ sudo gconftool-2 --direct \
      --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \
      --type bool \
      --set /apps/gnome-screensaver/lock_enabled true

Rationale:

Enabling the activation of the screen lock after an idle period ensures password entry will be required in order to access the system, preventing access by passersby.

Severity: medium

References: AC-11(a), 57

Remediation Shell script: (show)

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

    # Install GConf2 package if not installed
    if ! rpm -q GConf2; then
      yum -y install GConf2
    fi

    # Set the screensaver locking activation in the GNOME desktop when the
    # screensaver is activated
    gconftool-2 --direct \
                --config-source "xml:readwrite:/etc/gconf/gconf.xml.mandatory" \
                --type bool \
                --set /apps/gnome-screensaver/lock_enabled true

#### Implement Blank Screensaver [ref]rule

Run the following command to set the screensaver mode in the GNOME desktop to a blank screen:

    $ sudo gconftool-2 --direct \
      --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \
      --type string \
      --set /apps/gnome-screensaver/mode blank-only

Rationale:

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

Severity: low

References: AC-11(b), 60

Remediation Shell script: (show)

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

    # Install GConf2 package if not installed
    if ! rpm -q GConf2; then
      yum -y install GConf2
    fi

    # Set the screensaver mode in the GNOME desktop to a blank screen
    gconftool-2 --direct \
                --config-source "xml:readwrite:/etc/gconf/gconf.xml.mandatory" \
                --type string \
                --set /apps/gnome-screensaver/mode blank-only

### GNOME Media Settings [ref]group

GNOME media settings that apply to the graphical interface.

contains 2 rules

#### Disable GNOME Automounting [ref]rule

The system's default desktop environment, GNOME, will mount devices and removable media (such as DVDs, CDs and USB flash drives) whenever they are inserted into the system. Disable automount and autorun within GNOME by running the following:

    $ sudo gconftool-2 --direct \
      --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \
      --type bool \
      --set /apps/nautilus/preferences/media_automount false
    $ sudo gconftool-2 --direct \
      --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \
      --type bool \
      --set /apps/nautilus/preferences/media_autorun_never true

Rationale:

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

Severity: low

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

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

The system's default desktop environment, GNOME, uses a number of different thumbnailer programs to generate thumbnails for any new or modified content in an opened folder. The following command can disable the execution of these thumbnail applications:

    $ sudo gconftool-2 --direct \
      --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \
      --type bool \
      --set /desktop/gnome/thumbnailers/disable_all true

This effectively prevents an attacker from gaining access to a system through a flaw in GNOME'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

References: CM-7

### 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 46 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 11 rules

#### Add nodev Option to Non-Root Local 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 non-root local partitions.

Rationale:

The `nodev` mount option prevents files from being interpreted as character or block devices. The only legitimate location for device files is the `/dev` directory located on the root partition. The only exception to this is chroot jails, for which it is not advised to set `nodev` on these filesystems.

Severity: low

References: CM-7

Remediation Shell script: (show)

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

    # NOTE: Run-time reconfiguration of partitions' mount options is not possible.
    # After performing this remediation be sure to also subsequently reboot the
    # system as soon as possible for the remediation to take the effect!

    # Shortened ID for frequently used character class
    SP="[:space:]"

    # Load /etc/fstab's content with LABEL= and UUID= tags expanded to real
    # device names into FSTAB_REAL_DEVICES array splitting items by newline
    IFS=$'\n' FSTAB_REAL_DEVICES=($(findmnt --fstab --evaluate --noheadings))

    for line in ${FSTAB_REAL_DEVICES[@]}
    do
        # For each line:
        # * squeeze multiple space characters into one,
        # * split line content info four columns (target, source, fstype, and
        #   mount options) by space delimiter
        IFS=$' ' read TARGET SOURCE FSTYPE MOUNT_OPTIONS <<< "$(echo $line | tr -s ' ')"

        # Filter the targets according to the following criteria:
        # * don't include record for root partition,
        # * include the target only if it has the form of '/word.*' (not to include
        #   special entries like e.g swap),
        # * include the target only if its source has the form of '/dev.*'
        #   (to process only local partitions)
        if [[ ! $TARGET =~ ^\/$ ]] 		&&	# Don't include root partition
           [[ $TARGET =~ ^\/[A-Za-z0-9_] ]] &&	# Include if target =~ '/word.*'
           [[ $SOURCE =~ ^\/dev ]]			# Include if source =~ '/dev.*'
        then

            # Check the mount options column if it doesn't contain 'nodev' keyword yet
            if ! grep -q "nodev" <<< "$MOUNT_OPTIONS"
            then
                # Check if current mount options is empty string ('') meaning
                # particular /etc/fstab row contain just 'defaults' keyword
                if [[ ${#MOUNT_OPTIONS} == "0" ]]
                then
                    # If so, add 'defaults' back and append 'nodev' keyword
                    MOUNT_OPTIONS="defaults,nodev"
                else
                    # Otherwise append just 'nodev' keyword
                    MOUNT_OPTIONS="$MOUNT_OPTIONS,nodev"
                fi

                # Escape possible slash ('/') characters in target for use as sed
                # expression below
                TARGET_ESCAPED=${TARGET//$'/'/$'\/'}
                # This target doesn't contain 'nodev' in mount options yet (and meets
                # the above filtering criteria). Therefore obtain particular /etc/fstab's
                # row into FSTAB_TARGET_ROW variable separating the mount options field with
                # hash '#' character
                FSTAB_TARGET_ROW=$(sed -n "s/\(.*$TARGET_ESCAPED[$SP]\+$FSTYPE[$SP]\+\)\([^$SP]\+\)/\1#\2#/p" /etc/fstab)
                # Split the retrieved value by the hash '#' delimiter to get the
                # row's head & tail (i.e. columns other than mount options) which won't
                # get modified
                IFS=$'#' read TARGET_HEAD TARGET_OPTS TARGET_TAIL <<< "$FSTAB_TARGET_ROW"
                # Replace old mount options for particular /etc/fstab's row (for this target
                # and fstype) with new mount options
                sed -i "s#${TARGET_HEAD}\(.*\)${TARGET_TAIL}#${TARGET_HEAD}${MOUNT_OPTIONS}${TARGET_TAIL}#" /etc/fstab

            fi
        fi
    done

#### 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

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

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

#### 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

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

#### Add nodev Option to /tmp [ref]rule

The `nodev` mount option can be used to prevent device files from being created in `/tmp`. Legitimate character and block devices should not exist within temporary directories like `/tmp`. Add the `nodev` option to the fourth column of `/etc/fstab` for the line which controls mounting of `/tmp`.

Rationale:

The only legitimate location for device files is the `/dev` directory located on the root partition. The only exception to this is chroot jails.

Severity: low

References: CM-7, MP-2

Remediation Anaconda snippet: (show)

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

    part /tmp -mountoptions="nodev"

#### Add noexec Option to /tmp [ref]rule

The `noexec` mount option can be used to prevent binaries from being executed out of `/tmp`. Add the `noexec` option to the fourth column of `/etc/fstab` for the line which controls mounting of `/tmp`.

Rationale:

Allowing users to execute binaries from world-writable directories such as `/tmp` should never be necessary in normal operation and can expose the system to potential compromise.

Severity: low

References: CM-7, MP-2

#### Add nosuid Option to /tmp [ref]rule

The `nosuid` mount option can be used to prevent execution of setuid programs in `/tmp`. The SUID and SGID permissions should not be required in these world-writable directories. Add the `nosuid` option to the fourth column of `/etc/fstab` for the line which controls mounting of `/tmp`.

Rationale:

The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions.

Severity: low

References: CM-7, MP-2

#### Add nodev Option to /dev/shm [ref]rule

The `nodev` mount option can be used to prevent creation of device files in `/dev/shm`. Legitimate character and block devices should not exist within temporary directories like `/dev/shm`. Add the `nodev` option to the fourth column of `/etc/fstab` for the line which controls mounting of `/dev/shm`.

Rationale:

The only legitimate location for device files is the `/dev` directory located on the root partition. The only exception to this is chroot jails.

Severity: low

References: CM-7, MP-2

Remediation Shell script: (show)

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

    # Load /etc/fstab's /dev/shm row into DEV_SHM_FSTAB variable separating start &
    # end of the filesystem mount options (4-th field) with the '#' character
    DEV_SHM_FSTAB=$(sed -n "s/\(.*[[:space:]]\+\/dev\/shm[[:space:]]\+tmpfs[[:space:]]\+\)\([^[:space:]]\+\)/\1#\2#/p" /etc/fstab)

    #Rest of script can trash /etc/fstab if $DEV_SHM_FSTAB is empty, check before continuing.
    echo $DEV_SHM_FSTAB | grep -q -P '/dev/shm'
    if [ $? -eq 0 ]; then
    	# Save the:
    	# * 1-th, 2-nd, 3-rd fields into DEV_SHM_HEAD variable
    	# * 4-th field into DEV_SHM_OPTS variable, and
    	# * 5-th, and 6-th fields into DEV_SHM_TAIL variable
    	# splitting DEV_SHM_FSTAB variable value based on the '#' separator
    	IFS='#' read DEV_SHM_HEAD DEV_SHM_OPTS DEV_SHM_TAIL <<< "$DEV_SHM_FSTAB"

    	# Replace occurrence of 'defaults' key with the actual list of mount options
    	# for Red Hat Enterprise Linux 6
    	DEV_SHM_OPTS=${DEV_SHM_OPTS//defaults/rw,suid,dev,exec,auto,nouser,async,relatime}

    	# 'dev' option (not prefixed with 'no') present in the list?
    	echo $DEV_SHM_OPTS | grep -q -P '(?<!no)dev'
    	if [ $? -eq 0 ]
    	then
    	        # 'dev' option found, replace with 'nodev'
    	        DEV_SHM_OPTS=${DEV_SHM_OPTS//dev/nodev}
    	fi

    	# at least one 'nodev' present in the options list?
    	echo $DEV_SHM_OPTS | grep -q -v 'nodev'
    	if [ $? -eq 0 ]
    	then
    	        # 'nodev' not found yet, append it
    	        DEV_SHM_OPTS="$DEV_SHM_OPTS,nodev"
    	fi

    	# DEV_SHM_OPTS now contains final list of mount options. Replace original form of /dev/shm row
    	# in /etc/fstab with the corrected version
    	sed -i "s#${DEV_SHM_HEAD}\(.*\)${DEV_SHM_TAIL}#${DEV_SHM_HEAD}${DEV_SHM_OPTS}${DEV_SHM_TAIL}#" /etc/fstab
    fi

#### Add noexec Option to /dev/shm [ref]rule

The `noexec` mount option can be used to prevent binaries from being executed out of `/dev/shm`. It can be dangerous to allow the execution of binaries from world-writable temporary storage directories such as `/dev/shm`. Add the `noexec` option to the fourth column of `/etc/fstab` for the line which controls mounting of `/dev/shm`.

Rationale:

Allowing users to execute binaries from world-writable directories such as `/dev/shm` can expose the system to potential compromise.

Severity: low

References: CM-7, MP-2

Remediation Shell script: (show)

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

    # Load /etc/fstab's /dev/shm row into DEV_SHM_FSTAB variable separating start &
    # end of the filesystem mount options (4-th field) with the '#' character
    DEV_SHM_FSTAB=$(sed -n "s/\(.*[[:space:]]\+\/dev\/shm[[:space:]]\+tmpfs[[:space:]]\+\)\([^[:space:]]\+\)/\1#\2#/p" /etc/fstab)

    #Rest of script can trash /etc/fstab if $DEV_SHM_FSTAB is empty, check before continuing.
    echo $DEV_SHM_FSTAB | grep -q -P '/dev/shm'
    if [ $? -eq 0 ]; then
    	# Save the:
    	# * 1-th, 2-nd, 3-rd fields into DEV_SHM_HEAD variable
    	# * 4-th field into DEV_SHM_OPTS variable, and
    	# * 5-th, and 6-th fields into DEV_SHM_TAIL variable
    	# splitting DEV_SHM_FSTAB variable value based on the '#' separator
    	IFS='#' read DEV_SHM_HEAD DEV_SHM_OPTS DEV_SHM_TAIL <<< "$DEV_SHM_FSTAB"

    	# Replace occurrence of 'defaults' key with the actual list of mount options
    	# for Red Hat Enterprise Linux 6
    	DEV_SHM_OPTS=${DEV_SHM_OPTS//defaults/rw,suid,dev,exec,auto,nouser,async,relatime}

    	# 'exec' option (not prefixed with 'no') present in the list?
    	echo $DEV_SHM_OPTS | grep -q -P '(?<!no)exec'
    	if [ $? -eq 0 ]
    	then
    	        # 'exec' option found, replace with 'noexec'
    	        DEV_SHM_OPTS=${DEV_SHM_OPTS//exec/noexec}
    	fi

    	# at least one 'noexec' present in the options list?
    	echo $DEV_SHM_OPTS | grep -q -v 'noexec'
    	if [ $? -eq 0 ]
    	then
    	        # 'noexec' not found yet, append it
    	        DEV_SHM_OPTS="$DEV_SHM_OPTS,noexec"
    	fi

    	# DEV_SHM_OPTS now contains final list of mount options. Replace original form of /dev/shm row
    	# in /etc/fstab with the corrected version
    	sed -i "s#${DEV_SHM_HEAD}\(.*\)${DEV_SHM_TAIL}#${DEV_SHM_HEAD}${DEV_SHM_OPTS}${DEV_SHM_TAIL}#" /etc/fstab

    fi

#### Add nosuid Option to /dev/shm [ref]rule

The `nosuid` mount option can be used to prevent execution of setuid programs in `/dev/shm`. The SUID and SGID permissions should not be required in these world-writable directories. Add the `nosuid` option to the fourth column of `/etc/fstab` for the line which controls mounting of `/dev/shm`.

Rationale:

The presence of SUID and SGID executables should be tightly controlled. Users should not be able to execute SUID or SGID binaries from temporary storage partitions.

Severity: low

References: CM-7, MP-2

Remediation Shell script: (show)

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

    # Load /etc/fstab's /dev/shm row into DEV_SHM_FSTAB variable separating start &
    # end of the filesystem mount options (4-th field) with the '#' character
    DEV_SHM_FSTAB=$(sed -n "s/\(.*[[:space:]]\+\/dev\/shm[[:space:]]\+tmpfs[[:space:]]\+\)\([^[:space:]]\+\)/\1#\2#/p" /etc/fstab)

    #Rest of script can trash /etc/fstab if $DEV_SHM_FSTAB is empty, check before continuing.
    echo $DEV_SHM_FSTAB | grep -q -P '/dev/shm'
    if [ $? -eq 0 ]; then
    	# Save the:
    	# * 1-th, 2-nd, 3-rd fields into DEV_SHM_HEAD variable
    	# * 4-th field into DEV_SHM_OPTS variable, and
    	# * 5-th, and 6-th fields into DEV_SHM_TAIL variable
    	# splitting DEV_SHM_FSTAB variable value based on the '#' separator
    	IFS='#' read DEV_SHM_HEAD DEV_SHM_OPTS DEV_SHM_TAIL <<< "$DEV_SHM_FSTAB"

    	# Replace occurrence of 'defaults' key with the actual list of mount options
    	# for Red Hat Enterprise Linux 6
    	DEV_SHM_OPTS=${DEV_SHM_OPTS//defaults/rw,suid,dev,exec,auto,nouser,async,relatime}

    	# 'suid' option (not prefixed with 'no') present in the list?
    	echo $DEV_SHM_OPTS | grep -q -P '(?<!no)suid'
    	if [ $? -eq 0 ]
    	then
    	        # 'suid' option found, replace with 'nosuid'
    	        DEV_SHM_OPTS=${DEV_SHM_OPTS//suid/nosuid}
    	fi

    	# at least one 'nosuid' present in the options list?
    	echo $DEV_SHM_OPTS | grep -q -v 'nosuid'
    	if [ $? -eq 0 ]
    	then
    	        # 'nosuid' not found yet, append it
    	        DEV_SHM_OPTS="$DEV_SHM_OPTS,nosuid"
    	fi

    	# DEV_SHM_OPTS now contains final list of mount options. Replace original form of /dev/shm row
    	# in /etc/fstab with the corrected version
    	sed -i "s#${DEV_SHM_HEAD}\(.*\)${DEV_SHM_TAIL}#${DEV_SHM_HEAD}${DEV_SHM_OPTS}${DEV_SHM_TAIL}#" /etc/fstab
    fi

#### Bind Mount /var/tmp To /tmp [ref]rule

The `/var/tmp` directory is a world-writable directory. Bind-mount it to `/tmp` in order to consolidate temporary storage into one location protected by the same techniques as `/tmp`. To do so, edit `/etc/fstab` and add the following line:

    /tmp     /var/tmp     none     rw,nodev,noexec,nosuid,bind     0 0

See the `mount(8)` man page for further explanation of bind mounting. Rationale:

Having multiple locations for temporary storage is not required. Unless absolutely necessary to meet requirements, the storage location `/var/tmp` should be bind mounted to `/tmp` and thus share the same protections.

Severity: low

References: CM-7

Remediation Shell script: (show)

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

    # Delete particular /etc/fstab's row if /var/tmp is already configured to
    # represent a mount point (for some device or filesystem other than /tmp)
    if grep -q -P '.*\/var\/tmp.*' /etc/fstab
    then
      sed -i '/.*\/var\/tmp.*/d' /etc/fstab
    fi

    # Bind-mount /var/tmp to /tmp via /etc/fstab (preserving the /etc/fstab form)
    printf "%-24s%-24s%-8s%-32s%-3s\n" "/tmp" "/var/tmp" "none" "rw,nodev,noexec,nosuid,bind" "0 0" >> /etc/fstab

### 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 11 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: low

References: AC-19(a), AC-19(d), AC-19(e), 1250, 85

Remediation Shell script: (show)

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

    echo "install usb-storage /bin/true" > /etc/modprobe.d/usb-storage.conf

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/grub.conf` 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

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

#### 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

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

#### 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 chkconfig autofs off

Rationale:

Disabling the automounter permits the administrator to statically control filesystem mounting through `/etc/fstab`.

Severity: low

References: AC-19(a), AC-19(d), AC-19(e), 366

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

#### Disable Mounting of cramfs [ref]rule

To configure the system to prevent the `cramfs` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install cramfs /bin/true

This effectively prevents usage of this uncommon filesystem. Rationale:

Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.

Severity: low

References: CM-7

Remediation Shell script: (show)

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

    echo "install cramfs /bin/true" > /etc/modprobe.d/cramfs.conf

Remediation Ansible snippet: (show)

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

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

#### Disable Mounting of freevxfs [ref]rule

To configure the system to prevent the `freevxfs` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install freevxfs /bin/true

This effectively prevents usage of this uncommon filesystem. Rationale:

Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.

Severity: low

References: CM-7

Remediation Shell script: (show)

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

    echo "install freevxfs /bin/true" > /etc/modprobe.d/freevxfs.conf

Remediation Ansible snippet: (show)

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

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

#### Disable Mounting of jffs2 [ref]rule

To configure the system to prevent the `jffs2` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install jffs2 /bin/true

This effectively prevents usage of this uncommon filesystem. Rationale:

Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.

Severity: low

References: CM-7

Remediation Shell script: (show)

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

    echo "install jffs2 /bin/true" > /etc/modprobe.d/jffs2.conf

Remediation Ansible snippet: (show)

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

    - name: Ensure kernel module 'jffs2' is disabled
      lineinfile:
        create=yes
        dest="/etc/modprobe.d/{{item}}.conf"
        regexp="{{item}}"
        line="install {{item}} /bin/true"
      with_items:
        - jffs2

#### Disable Mounting of hfs [ref]rule

To configure the system to prevent the `hfs` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install hfs /bin/true

This effectively prevents usage of this uncommon filesystem. Rationale:

Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.

Severity: low

References: CM-7

Remediation Shell script: (show)

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

    echo "install hfs /bin/true" > /etc/modprobe.d/hfs.conf

Remediation Ansible snippet: (show)

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

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

#### Disable Mounting of hfsplus [ref]rule

To configure the system to prevent the `hfsplus` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install hfsplus /bin/true

This effectively prevents usage of this uncommon filesystem. Rationale:

Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.

Severity: low

References: CM-7

Remediation Shell script: (show)

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

    echo "install hfsplus /bin/true" > /etc/modprobe.d/hfsplus.conf

Remediation Ansible snippet: (show)

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

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

#### Disable Mounting of squashfs [ref]rule

To configure the system to prevent the `squashfs` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install squashfs /bin/true

This effectively prevents usage of this uncommon filesystem. Rationale:

Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.

Severity: low

References: CM-7

Remediation Shell script: (show)

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

    echo "install squashfs /bin/true" > /etc/modprobe.d/squashfs.conf

Remediation Ansible snippet: (show)

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

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

#### Disable Mounting of udf [ref]rule

To configure the system to prevent the `udf` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install udf /bin/true

This effectively prevents usage of this uncommon filesystem. Rationale:

Linux kernel modules which implement filesystems that are not needed by the local system should be disabled.

Severity: low

References: CM-7

Remediation Shell script: (show)

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

    echo "install udf /bin/true" > /etc/modprobe.d/udf.conf

Remediation Ansible snippet: (show)

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

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

### 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 21 rules

### Verify Permissions on Files with Local Account Information and Credentials [ref]group

The default restrictive permissions for files which act as important security databases such as `passwd`, `shadow`, `group`, and `gshadow` files must be maintained. Many utilities need read access to the `passwd` file in order to function properly, but read access to the `shadow` file allows malicious attacks against system passwords, and should never be enabled.

contains 12 rules

#### Verify User Who Owns shadow File [ref]rule

To properly set the owner of `/etc/shadow`, run the command:

    $ sudo chown root /etc/shadow

Rationale:

The `/etc/shadow` file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture.

Severity: medium

References: AC-6, 225

Remediation Shell script: (show)

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

    chown root /etc/shadow

#### Verify Group Who Owns shadow File [ref]rule

To properly set the group owner of `/etc/shadow`, run the command:

    $ sudo chgrp root /etc/shadow

Rationale:

The `/etc/shadow` file stores password hashes. Protection of this file is critical for system security.

Severity: medium

References: AC-6, 225

Remediation Shell script: (show)

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

    chgrp root /etc/shadow

#### Verify Permissions on shadow File [ref]rule

To properly set the permissions of `/etc/shadow`, run the command:

    $ sudo chmod 0000 /etc/shadow

Rationale:

The `/etc/shadow` file contains the list of local system accounts and stores password hashes. Protection of this file is critical for system security. Failure to give ownership of this file to root provides the designated owner with access to sensitive information which could weaken the system security posture.

Severity: medium

References: AC-6, 225

Remediation Shell script: (show)

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

    chmod 0000 /etc/shadow

Remediation Ansible snippet: (show)

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

    - name: Ensure permission 0000 on /etc/shadow
      file:
        path="{{item}}"
        mode=0000
      with_items:
        - /etc/shadow

#### Verify User Who Owns group File [ref]rule

To properly set the owner of `/etc/group`, run the command:

    $ sudo chown root /etc/group

Rationale:

The `/etc/group` file contains information regarding groups that are configured on the system. Protection of this file is important for system security.

Severity: medium

References: AC-6

Remediation Shell script: (show)

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

    chown root /etc/group

#### Verify Group Who Owns group File [ref]rule

To properly set the group owner of `/etc/group`, run the command:

    $ sudo chgrp root /etc/group

Rationale:

The `/etc/group` file contains information regarding groups that are configured on the system. Protection of this file is important for system security.

Severity: medium

References: AC-6, 225

Remediation Shell script: (show)

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

    chgrp root /etc/group

#### Verify Permissions on group File [ref]rule

To properly set the permissions of `/etc/group`, run the command:

    $ sudo chmod 644 /etc/group

Rationale:

The `/etc/group` file contains information regarding groups that are configured on the system. Protection of this file is important for system security.

Severity: medium

References: AC-6, 225

Remediation Shell script: (show)

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

    chmod 644 /etc/group

#### Verify User Who Owns gshadow File [ref]rule

To properly set the owner of `/etc/gshadow`, run the command:

    $ sudo chown root /etc/gshadow

Rationale:

The `/etc/gshadow` file contains group password hashes. Protection of this file is critical for system security.

Severity: medium

References: AC-6, 366

Remediation Shell script: (show)

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

    chown root /etc/gshadow

#### Verify Group Who Owns gshadow File [ref]rule

To properly set the group owner of `/etc/gshadow`, run the command:

    $ sudo chgrp root /etc/gshadow

Rationale:

The `/etc/gshadow` file contains group password hashes. Protection of this file is critical for system security.

Severity: medium

References: AC-6, 225

Remediation Shell script: (show)

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

    chgrp root /etc/gshadow

#### Verify Permissions on gshadow File [ref]rule

To properly set the permissions of `/etc/gshadow`, run the command:

    $ sudo chmod 0000 /etc/gshadow

Rationale:

The `/etc/gshadow` file contains group password hashes. Protection of this file is critical for system security.

Severity: medium

References: AC-6, 225

Remediation Shell script: (show)

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

    chmod 0000 /etc/gshadow

#### Verify User Who Owns passwd File [ref]rule

To properly set the owner of `/etc/passwd`, run the command:

    $ sudo chown root /etc/passwd

Rationale:

The `/etc/passwd` file contains information about the users that are configured on the system. Protection of this file is critical for system security.

Severity: medium

References: AC-6, 225

Remediation Shell script: (show)

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

    chown root /etc/passwd

#### Verify Group Who Owns passwd File [ref]rule

To properly set the group owner of `/etc/passwd`, run the command:

    $ sudo chgrp root /etc/passwd

Rationale:

The `/etc/passwd` file contains information about the users that are configured on the system. Protection of this file is critical for system security.

Severity: medium

References: AC-6, 225

Remediation Shell script: (show)

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

    chgrp root /etc/passwd

#### Verify Permissions on passwd File [ref]rule

To properly set the permissions of `/etc/passwd`, run the command:

    $ sudo chmod 0644 /etc/passwd

Rationale:

If the `/etc/passwd` file is writable by a group-owner or the world the risk of its compromise is increased. The file contains the list of accounts on the system and associated information, and protection of this file is critical for system security.

Severity: medium

References: AC-6, 225

Remediation Shell script: (show)

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

    chmod 0644 /etc/passwd

### Verify File Permissions Within Some Important Directories [ref]group

Some directories contain files whose confidentiality or integrity is notably important and may also be susceptible to misconfiguration over time, particularly if unpackaged software is installed. As such, an argument exists to verify that files' permissions within these directories remain configured correctly and restrictively.

contains 4 rules

#### Verify that Shared Library Files Have Restrictive Permissions [ref]rule

System-wide shared library files, which are linked to executables during process load time or run time, are stored in the following directories by default:

    /lib
    /lib64
    /usr/lib
    /usr/lib64

Kernel modules, which can be added to the kernel during runtime, are stored in `/lib/modules`. All files in these directories should not be group-writable or world-writable. If any file in these directories is found to be group-writable or world-writable, correct its permission with the following command:

    $ sudo chmod go-w FILE

Rationale:

Files from shared library directories are loaded into the address space of processes (including privileged ones) or of the kernel itself at runtime. Restrictive permissions are necessary to protect the integrity of the system.

Severity: medium

References: AC-6, 1499

Remediation Shell script: (show)

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

    DIRS="/lib /lib64 /usr/lib /usr/lib64"
    for dirPath in $DIRS; do
    	find $dirPath -perm /022 -type f -exec chmod go-w '{}' \;
    done

#### Verify that Shared Library Files Have Root Ownership [ref]rule

System-wide shared library files, which are linked to executables during process load time or run time, are stored in the following directories by default:

    /lib
    /lib64
    /usr/lib
    /usr/lib64

Kernel modules, which can be added to the kernel during runtime, are also stored in `/lib/modules`. All files in these directories should be owned by the `root` user. If the directory, or any file in these directories, is found to be owned by a user other than root correct its ownership with the following command:

    $ sudo chown root FILE

Rationale:

Files from shared library directories are loaded into the address space of processes (including privileged ones) or of the kernel itself at runtime. Proper ownership is necessary to protect the integrity of the system.

Severity: medium

References: AC-6, 1499

Remediation Shell script: (show)

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

    for LIBDIR in /usr/lib /usr/lib64 /lib /lib64
    do
      if [ -d $LIBDIR ]
      then
        find -L $LIBDIR \! -user root -exec chown root {} \;
      fi
    done

#### Verify that System Executables Have Restrictive Permissions [ref]rule

System executables are stored in the following directories by default:

    /bin
    /sbin
    /usr/bin
    /usr/libexec
    /usr/local/bin
    /usr/local/sbin
    /usr/sbin

All files in these directories should not be group-writable or world-writable. If any file FILE in these directories is found to be group-writable or world-writable, correct its permission with the following command:

    $ sudo chmod go-w FILE

Rationale:

System binaries are executed by privileged users, as well as system services, and restrictive permissions are necessary to ensure execution of these programs cannot be co-opted.

Severity: medium

References: AC-6, 1499

Remediation Shell script: (show)

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

    DIRS="/bin /usr/bin /usr/local/bin /sbin /usr/sbin /usr/local/sbin /usr/libexec"
    for dirPath in $DIRS; do
    	find "$dirPath" -perm /022 -exec chmod go-w '{}' \;
    done

#### Verify that System Executables Have Root Ownership [ref]rule

System executables are stored in the following directories by default:

    /bin
    /sbin
    /usr/bin
    /usr/libexec
    /usr/local/bin
    /usr/local/sbin
    /usr/sbin

All files in these directories should be owned by the `root` user. If any file FILE in these directories is found to be owned by a user other than root, correct its ownership with the following command:

    $ sudo chown root FILE

Rationale:

System binaries are executed by privileged users as well as system services, and restrictive permissions are necessary to ensure that their execution of these programs cannot be co-opted.

Severity: medium

References: AC-6, 1499

Remediation Shell script: (show)

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

    find /bin/ \
    /usr/bin/ \
    /usr/local/bin/ \
    /sbin/ \
    /usr/sbin/ \
    /usr/local/sbin/ \
    /usr/libexec \
    \! -user root -execdir chown root {} \;

#### Verify that All World-Writable Directories Have Sticky Bits Set [ref]rule

When the so-called 'sticky bit' is set on a directory, only the owner of a given file may remove that file from the directory. Without the sticky bit, any user with write access to a directory may remove any file in the directory. Setting the sticky bit prevents users from removing each other's files. In cases where there is no reason for a directory to be world-writable, a better solution is to remove that permission rather than to set the sticky bit. However, if a directory is used by a particular application, consult that application's documentation instead of blindly changing modes.
To set the sticky bit on a world-writable directory DIR, run the following command:

    $ sudo chmod +t DIR

Rationale:

Failing to set the sticky bit on public directories allows unauthorized users to delete files in the directory structure.
The only authorized public directories are those temporary directories supplied with the system, or those designed to be temporary file repositories. The setting is normally reserved for directories used by the system, by users for temporary file storage (such as `/tmp`), and for directories requiring global read/write access.

Severity: low

References: AC-6

#### Ensure No World-Writable Files Exist [ref]rule

It is generally a good idea to remove global (other) write access to a file when it is discovered. However, check with documentation for specific applications before making changes. Also, monitor for recurring world-writable files, as these may be symptoms of a misconfigured application or user account.

Rationale:

Data in world-writable files can be modified by any user on the system. In almost all circumstances, files can be configured using a combination of user and group permissions to support whatever legitimate access is needed without the risk caused by world-writable files.

Severity: medium

References: AC-6

#### 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: low

References: AC-6, 224

#### 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: low

References: AC-6, 224

#### 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

References: AC-6

### 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 3 rules

### Daemon Umask [ref]group

The umask is a per-process setting which limits the default permissions for creation of new files and directories. The system includes initialization scripts which set the default umask for system daemons.

contains 1 rule

#### Set Daemon Umask [ref]rule

The file `/etc/init.d/functions` includes initialization parameters for most or all daemons started at boot time. The default umask of 022 prevents creation of group- or world-writable files. To set the default umask for daemons, edit the following line, inserting 022 or 027 for umask appropriately:

    umask 022

Setting the umask to too restrictive a setting can cause serious errors at runtime. Many daemons on the system already individually restrict themselves to a umask of 077 in their own init scripts. Rationale:

The umask influences the permissions assigned to files created by a process at run time. An unnecessarily permissive umask could result in files being created with insecure permissions.

Severity: low

References: AC-6

Remediation Shell script: (show)

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

    var_umask_for_daemons="022"

    grep -q ^umask /etc/init.d/functions && \
      sed -i "s/umask.*/umask $var_umask_for_daemons/g" /etc/init.d/functions
    if ! [ $? -eq 0 ]; then
        echo "umask $var_umask_for_daemons" >> /etc/init.d/functions
    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 and controlled through `sysctl` variables `kernel.exec-shield` and `kernel.randomize_va_space`.

contains 2 rules

#### Enable ExecShield [ref]rule

To set the runtime status of the `kernel.exec-shield` kernel parameter, run the following command:

    $ sudo sysctl -w kernel.exec-shield=1

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

    kernel.exec-shield = 1

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.

Severity: medium

References: SC-39, 2530

Remediation Shell script: (show)

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

    #
    # Set runtime for kernel.exec-shield
    #
    /sbin/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.conf
    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

References: SC-30(2)

Remediation Shell script: (show)

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

    #
    # Set runtime for kernel.randomize_va_space
    #
    /sbin/sysctl -q -n -w kernel.randomize_va_space=2

    #
    # If kernel.randomize_va_space present in /etc/sysctl.conf, change value to "2"
    #	else, add "kernel.randomize_va_space = 2" to /etc/sysctl.conf
    #
    if grep --silent ^kernel.randomize_va_space /etc/sysctl.conf ; then
    	sed -i 's/^kernel.randomize_va_space.*/kernel.randomize_va_space = 2/g' /etc/sysctl.conf
    else
    	echo -e "\n# Set kernel.randomize_va_space to 2 per security requirements" >> /etc/sysctl.conf
    	echo "kernel.randomize_va_space = 2" >> /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 6, 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.

contains 6 rules

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

SELinux can be disabled at boot time by an argument in `/etc/grub.conf`. 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

References: AC-3, AC-3(3), AC-6, AU-9, 22, 32

Remediation Shell script: (show)

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

    sed -i --follow-symlinks "s/selinux=0//gI" /etc/grub.conf
    sed -i --follow-symlinks "s/enforcing=0//gI" /etc/grub.conf

#### 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: medium

References: AC-3, AC-3(3), AC-4, AC-6, AU-9, 22, 32, 26

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-26969-6' '%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: low

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

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-26875-5' '%s=%s'

#### Enable the SELinux Context Restoration Service (restorecond) [ref]rule

The `restorecond` service utilizes `inotify` to look for the creation of new files listed in the `/etc/selinux/restorecond.conf` configuration file. When a file is created, `restorecond` ensures the file receives the proper SELinux security context. The `restorecond` service can be enabled with the following command:

    $ sudo chkconfig --level 2345 restorecond on

Rationale:

The `restorecond` service helps ensure that the default SELinux file context is applied to files. This allows automatic correction of file contexts created by some programs.

Severity: low

References: AC-3, AC-3(3), AC-4, AC-6, AU-9

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 restorecond

Remediation Ansible snippet: (show)

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

    - name: Enable service restorecond
      service:
        name="{{item}}"
        enabled="yes"
        state="started"
      with_items:
        - restorecond

#### 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

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

#### Ensure No Device Files are Unknown to 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 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: low

References: AC-6, AU-9, CM-7, 22, 32

### 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 6.

contains 36 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 12 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

#### 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

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

References: AC-6(2), 770

Remediation Shell script: (show)

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

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

#### Ensure that System Accounts Do Not Run a Shell Upon Login [ref]rule

Some accounts are not associated with a human user of the system, and exist to perform some administrative function. Should an attacker be able to log into these accounts, they should not be granted access to a shell.
The login shell for each local account is stored in the last field of each line in `/etc/passwd`. System accounts are those user accounts with a user ID less than UID_MIN, where value of the UID_MIN directive is set in /etc/login.defs configuration file. In the default configuration UID_MIN is set to 500, thus system accounts are those user accounts with a user ID less than 500. The user ID is stored in the third field. If any system account SYSACCT (other than root) has a login shell, disable it with the command:

    $ sudo usermod -s /sbin/nologin SYSACCT

Warning: Do not perform the steps in this section on the root account. Doing so might cause the system to become inaccessible.
Rationale:

Ensuring shells are not given to system accounts upon login makes it more difficult for attackers to make use of system accounts.

Severity: medium

References: AC-2, 178

#### 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.

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: medium

References: AC-6, IA-2(1), 366

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 2 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 onto 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

References: IA-5(b), IA-5(c), IA-5(1)(a)

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

References: IA-5(h), 201

### 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 4 rules

#### Set Password Minimum Length in login.defs [ref]rule

To specify password length requirements for new accounts, edit the file `/etc/login.defs` and add or correct the following lines:

    PASS_MIN_LEN

As of the DISA Red Hat 6 STIG - Ver 1, Rel 13 (28-OCT-2016), the DoD requirement is now `15`. The FISMA requirement is `12`. If a program consults `/etc/login.defs` and also another PAM module (such as `pam_cracklib`) during a password change operation, then the most restrictive must be satisfied. See PAM section for more information about enforcing password quality requirements. Rationale:

Requiring a minimum password length makes password cracking attacks more difficult by ensuring a larger search space. However, any security benefit from an onerous requirement must be carefully weighed against usability problems, support costs, or counterproductive behavior that may result.

Severity: medium

References: IA-5(f), IA-5(1)(a), 205

Remediation Shell script: (show)

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

    var_accounts_password_minlen_login_defs=""

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

#### 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:

    PASS_MIN_DAYS 7

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

Setting the minimum password age protects against users cycling back to a favorite password after satisfying the password reuse requirement.

Severity: medium

References: IA-5(f), IA-5(1)(d), 198

Remediation Shell script: (show)

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

    var_accounts_minimum_age_login_defs="7"

    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:

    PASS_MAX_DAYS 90

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

Setting the password maximum age ensures users are required to periodically change their passwords. This could possibly decrease the utility of a stolen password. Requiring shorter password lifetimes increases the risk of users writing down the password in a convenient location subject to physical compromise.

Severity: medium

References: IA-5(f), IA-5(g), IA-5(1)(d), 180, 199, 76

Remediation Shell script: (show)

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

    var_accounts_maximum_age_login_defs="90"

    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 Password Warning Age [ref]rule

To specify how many days prior to password expiration that a warning will be issued to users, edit the file `/etc/login.defs` and add or correct the following line:

    PASS_WARN_AGE 7

The DoD requirement is 7. Rationale:

Setting the password warning age enables users to make the change at a practical time.

Severity: low

References: AC-2(2), IA-5(f)

Remediation Shell script: (show)

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

    var_accounts_password_warn_age_login_defs="7"

    grep -q ^PASS_WARN_AGE /etc/login.defs && \
      sed -i "s/PASS_WARN_AGE.*/PASS_WARN_AGE     $var_accounts_password_warn_age_login_defs/g" /etc/login.defs
    if ! [ $? -eq 0 ]; then
        echo "PASS_WARN_AGE      $var_accounts_password_warn_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: low

References: AC-2(2), AC-2(3), 16, 17, 795

Remediation Shell script: (show)

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

    var_account_disable_post_pw_expiration="40"

    grep -q ^INACTIVE /etc/default/useradd && \
      sed -i "s/INACTIVE.*/INACTIVE=$var_account_disable_post_pw_expiration/g" /etc/default/useradd
    if ! [ $? -eq 0 ]; then
        echo "INACTIVE=$var_account_disable_post_pw_expiration" >> /etc/default/useradd
    fi

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

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. Rationale:

When temporary and emergency accounts are created, there is a risk they may remain in place and active after the need for them no longer exists. Account expiration greatly reduces the risk of accounts being misused or hijacked.

Severity: low

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

### 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 13 rules

### Set Password Quality Requirements [ref]group

The default `pam_cracklib` 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 man page `pam_cracklib(8)` provides information on the capabilities and configuration of each.

contains 6 rules

### Set Password Quality Requirements, if using pam_cracklib [ref]group

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

    password requisite pam_cracklib.so try_first_pass retry=3

and then alter it to read:

    password required pam_cracklib.so try_first_pass retry=3 maxrepeat=3 minlen=14 dcredit=-1 ucredit=-1 ocredit=-1 lcredit=-1 difok=4

If no such line exists, add one as the first line of the password section in `/etc/pam.d/system-auth`. 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 6 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_cracklib.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

References: IA-5(c), 1092

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

The pam_cracklib 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_cracklib will grant +1 additional length credit for each digit. Add `dcredit=-1` after pam_cracklib.so to require use of a digit in passwords.

Rationale:

Requiring digits makes password guessing attacks more difficult by ensuring a larger search space.

Severity: low

References: IA-5(b), IA-5(c), 194

Remediation Shell script: (show)

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

    var_password_pam_dcredit="-1"

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

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

The pam_cracklib 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_cracklib will grant +1 additional length credit for each uppercase character. Add `ucredit=-1` after pam_cracklib.so to require use of an upper case character in passwords.

Rationale:

Requiring a minimum number of uppercase characters makes password guessing attacks more difficult by ensuring a larger search space.

Severity: low

References: IA-5(b), IA-5(c), IA-5(1)(a), 192

Remediation Shell script: (show)

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

    var_password_pam_ucredit="-2"

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

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

The pam_cracklib 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_cracklib will grant +1 additional length credit for each special character. Add `ocredit=-2` after pam_cracklib.so to require use of a special character in passwords.

Rationale:

Requiring a minimum number of special characters makes password guessing attacks more difficult by ensuring a larger search space.

Severity: low

References: IA-5(b), IA-5(c), IA-5(1)(a), 1619, 266

Remediation Shell script: (show)

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

    var_password_pam_ocredit="-2"

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

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

The pam_cracklib 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_cracklib will grant +1 additional length credit for each lowercase character. Add `lcredit=-1` after pam_cracklib.so to require use of a lowercase character in passwords.

Rationale:

Requiring a minimum number of lowercase characters makes password guessing attacks more difficult by ensuring a larger search space.

Severity: low

References: IA-5(b), IA-5(c), IA-5(1)(a), 193

Remediation Shell script: (show)

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

    var_password_pam_lcredit="-2"

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

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

The pam_cracklib module's `difok` parameter controls requirements for usage of different characters during a password change. Add `difok=3` after pam_cracklib.so to require differing characters when changing passwords. The DoD requirement is `4`.

Rationale:

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: low

References: IA-5(b), IA-5(c), IA-5(1)(b), 195

Remediation Shell script: (show)

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

    var_password_pam_difok="3"

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

### 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 4 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=900 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=900 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

References: AC-7(a), 44

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=900 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=900 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

References: AC-7(b), 47

Remediation Shell script: (show)

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

    var_accounts_passwords_pam_faillock_unlock_time="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, 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

#### Set Interval For Counting Failed Password Attempts [ref]rule

Utilizing `pam_faillock.so`, the `fail_interval` directive configures the system to lock out accounts after a number of incorrect login attempts. 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=900 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=900 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 within a specific period of time prevents direct password guessing attacks.

Severity: medium

References: AC-7(a), 1452

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

References: IA-5(f), IA-5(1)(e), 200

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 Password Hashing Algorithm in /etc/pam.d/system-auth [ref]rule

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:

Using a stronger hashing algorithm makes password cracking attacks more difficult.

Severity: medium

References: IA-5(b), IA-5(c), IA-5(1)(c), IA-7, 803

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:

Using a stronger hashing algorithm makes password cracking attacks more difficult.

Severity: medium

References: IA-5(b), IA-5(c), IA-5(1)(c), IA-7, 803

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:

Using a stronger hashing algorithm makes password cracking attacks more difficult.

Severity: medium

References: IA-5(b), IA-5(c), IA-5(1)(c), IA-7, 803

### 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 1 rule

#### Set Interactive Session Timeout [ref]rule

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.

Rationale:

Severity: low

### 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 7 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 GRUB. 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 4 rules

#### Verify /etc/grub.conf User Ownership [ref]rule

The file `/etc/grub.conf` should be owned by the `root` user to prevent destruction or modification of the file. To properly set the owner of `/etc/grub.conf`, run the command:

    $ sudo chown root /etc/grub.conf

Rationale:

Only root should be able to modify important boot parameters.

Severity: medium

References: AC-6(7), 225

Remediation Shell script: (show)

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

    chown root /etc/grub.conf

#### Verify /etc/grub.conf Group Ownership [ref]rule

The file `/etc/grub.conf` should be group-owned by the `root` group to prevent destruction or modification of the file. To properly set the group owner of `/etc/grub.conf`, run the command:

    $ sudo chgrp root /etc/grub.conf

Rationale:

The `root` group is a highly-privileged group. Furthermore, the group-owner of this file should not have any access privileges anyway.

Severity: medium

References: AC-6(7), 225

Remediation Shell script: (show)

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

    chgrp root /etc/grub.conf

#### Verify /boot/grub/grub.conf Permissions [ref]rule

File permissions for `/boot/grub/grub.conf` should be set to 600, which is the default. To properly set the permissions of `/boot/grub/grub.conf`, run the command:

    $ sudo chmod 600 /boot/grub/grub.conf

Rationale:

Proper permissions ensure that only the root user can modify important boot parameters.

Severity: medium

References: AC-6(7), 225

Remediation Shell script: (show)

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

    chmod 600 /boot/grub/grub.conf

#### Set Boot Loader Password [ref]rule

The grub boot loader should have password protection enabled to protect boot-time settings. To do so, select a password and then generate a hash from it by running the following command:

    $ grub-crypt --sha-512

When prompted to enter a password, insert the following line into `/etc/grub.conf` immediately after the header comments. (Use the output from `grub-crypt` as the value of password-hash):

    password --encrypted password-hash

NOTE: To meet FISMA Moderate, the bootloader password MUST differ from the root password. 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.

Severity: medium

References: IA-2(1), IA-5(e) AC-3, 213

### 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 1 rule

### 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:

Installing `screen` ensures a console locking capability is available for users who may need to suspend console logins.

Severity: low

References: 58

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

#### 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.
To require entry of the root password even if the system is started in single-user mode, add or correct the following line in the file `/etc/sysconfig/init`:

    SINGLE=/sbin/sulogin

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

References: IA-2(1), AC-3, 213

Remediation Shell script: (show)

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

    grep -q ^SINGLE /etc/sysconfig/init && \
      sed -i "s/SINGLE.*/SINGLE=\/sbin\/sulogin/g" /etc/sysconfig/init
    if ! [ $? -eq 0 ]; then
        echo "SINGLE=/sbin/sulogin" >> /etc/sysconfig/init
    fi

#### Disable Interactive Boot [ref]rule

To disable the ability for users to perform interactive startups, perform both of the following:

1. Edit the file `/etc/sysconfig/init`. Add or correct the line:

       PROMPT=no

2. Inspect the kernel boot arguments (which follow the word `kernel`) in `/etc/grub.conf` and ensure the `confirm` argument is not present.

Both the `PROMPT` option of the `/etc/sysconfig/init` file and the `confirm` kernel boot argument of the `/etc/grub.conf` file allow the console user to perform an interactive system startup, in which it is possible to select the set of services which are started on boot. Rationale:

Using interactive boot, the console user could disable auditing, firewalls, or other services, weakening system security.

Severity: medium

References: SC-2, AC-3, 213

Remediation Shell script: (show)

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

    # Ensure value of PROMPT key in /etc/sysconfig/init is set to 'no'
    grep -q ^PROMPT /etc/sysconfig/init && \
      sed -i "s/PROMPT.*/PROMPT=no/g" /etc/sysconfig/init
    if ! [ $? -eq 0 ]; then
        echo "PROMPT=no" >> /etc/sysconfig/init
    fi

    # Ensure 'confirm' kernel boot argument is not present in some of
    # kernel lines in /etc/grub.conf
    sed -i --follow-symlinks "s/confirm//gI" /etc/grub.conf

### 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 GNOME 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 GUI Warning Banner [ref]rule

To enable displaying a login warning banner in the GNOME Display Manager's login screen, run the following command:

    $ sudo gconftool-2 --direct \
      --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \
      --type bool \
      --set /apps/gdm/simple-greeter/banner_message_enable true

To display a banner, this setting must be enabled and then banner text must also be set. Rationale:

An appropriate warning message reinforces policy awareness during the login process and facilitates possible legal action against attackers.

Severity: medium

References: AC-8(a), AC-8(b), AC-8(c), 48, 50

Remediation Shell script: (show)

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

    # Install GConf2 package if not installed
    if ! rpm -q GConf2; then
      yum -y install GConf2
    fi

    # Enable displaying of a login warning banner in the GNOME Display Manager's
    # login screen
    gconftool-2 --direct \
                --config-source "xml:readwrite:/etc/gconf/gconf.xml.mandatory" \
                --type bool \
                --set /apps/gdm/simple-greeter/banner_message_enable true

#### Set GUI Warning Banner Text [ref]rule

To set the text shown by the GNOME Display Manager in the login screen, run the following command:

    $ sudo gconftool-2 --direct \
      --config-source xml:readwrite:/etc/gconf/gconf.xml.mandatory \
      --type string \
      --set /apps/gdm/simple-greeter/banner_message_text \
      "Text of the warning banner here"

When entering a warning banner that spans several lines, remember to begin and end the string with `"`. This command writes directly either to the `/etc/gconf/gconf.xml.mandatory/%gconf-tree.xml` if it exists or to the file `/etc/gconf/gconf.xml.mandatory/apps/gdm/simple-greeter/%gconf.xml`. Either of these files can later be edited directly if necessary. Rationale:

An appropriate warning message reinforces policy awareness during the login process and facilitates possible legal action against attackers.

Severity: medium

References: AC-8(a), AC-8(b), AC-8(c), 48, 1384, 1385, 1386, 1387, 1388

Remediation Shell script: (show)

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

    login_banner_text="--[\s\n]+WARNING[\s\n]+--[\s\n]*This[\s\n]+system[\s\n]+is[\s\n]+for[\s\n]+the[\s\n]+use[\s\n]+of[\s\n]+authorized[\s\n]+users[\s\n]+only.[\s\n]+Individuals[\s\n]*using[\s\n]+this[\s\n]+computer[\s\n]+system[\s\n]+without[\s\n]+authority[\s\n]+or[\s\n]+in[\s\n]+excess[\s\n]+of[\s\n]+their[\s\n]*authority[\s\n]+are[\s\n]+subject[\s\n]+to[\s\n]+having[\s\n]+all[\s\n]+their[\s\n]+activities[\s\n]+on[\s\n]+this[\s\n]+system[\s\n]*monitored[\s\n]+and[\s\n]+recorded[\s\n]+by[\s\n]+system[\s\n]+personnel.[\s\n]+Anyone[\s\n]+using[\s\n]+this[\s\n]*system[\s\n]+expressly[\s\n]+consents[\s\n]+to[\s\n]+such[\s\n]+monitoring[\s\n]+and[\s\n]+is[\s\n]+advised[\s\n]+that[\s\n]*if[\s\n]+such[\s\n]+monitoring[\s\n]+reveals[\s\n]+possible[\s\n]+evidence[\s\n]+of[\s\n]+criminal[\s\n]+activity[\s\n]*system[\s\n]+personal[\s\n]+may[\s\n]+provide[\s\n]+the[\s\n]+evidence[\s\n]+of[\s\n]+such[\s\n]+monitoring[\s\n]+to[\s\n]+law[\s\n]*enforcement[\s\n]+officials."

    # Install GConf2 package if not installed
    if ! rpm -q GConf2; then
      yum -y install GConf2
    fi

    # Expand the login_banner_text value - there was a regular-expression
    # matching various banners, needs to be expanded
    banner_expanded=$(echo "$login_banner_text" | sed 's/\[\\s\\n\][*+]/ /g;s/\\//g;')

    # Set the text shown by the GNOME Display Manager in the login screen
    gconftool-2 --direct \
                --config-source "xml:readwrite:/etc/gconf/gconf.xml.mandatory" \
                --type string \
                --set /apps/gdm/simple-greeter/banner_message_text "${banner_expanded}"

#### 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:
`Use of this or any other DoD interest computer system constitutes consent to monitoring at all times.
This is a DoD interest computer system. All DoD interest computer systems and related equipment are intended for the communication, transmission, processing, and storage of official U.S. Government or other authorized information only. All DoD interest computer systems are subject to monitoring at all times to ensure proper functioning of equipment and systems including security devices and systems, to prevent unauthorized use and violations of statutes and security regulations, to deter criminal activity, and for other similar purposes. Any user of a DoD interest computer system should be aware that any information placed in the system is subject to monitoring and is not subject to any expectation of privacy.
If monitoring of this or any other DoD interest computer system reveals possible evidence of violation of criminal statutes, this evidence and any other related information, including identification information about the user, may be provided to law enforcement officials. If monitoring of this or any other DoD interest computer systems reveals violations of security regulations or unauthorized use, employees who violate security regulations or make unauthorized use of DoD interest computer systems are subject to appropriate disciplinary action.
Use of this or any other DoD interest computer system constitutes consent to monitoring at all times.`
OR:
`I've read & consent to terms in IS user agreem't.`

Rationale:

An appropriate warning message reinforces policy awareness during the login process and facilitates possible legal action against attackers.

Severity: medium

References: AC-8(a), AC-8(b), AC-8(c), 48, 1384, 1385, 1386, 1387, 1388

Remediation Shell script: (show)

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

    login_banner_text="--[\s\n]+WARNING[\s\n]+--[\s\n]*This[\s\n]+system[\s\n]+is[\s\n]+for[\s\n]+the[\s\n]+use[\s\n]+of[\s\n]+authorized[\s\n]+users[\s\n]+only.[\s\n]+Individuals[\s\n]*using[\s\n]+this[\s\n]+computer[\s\n]+system[\s\n]+without[\s\n]+authority[\s\n]+or[\s\n]+in[\s\n]+excess[\s\n]+of[\s\n]+their[\s\n]*authority[\s\n]+are[\s\n]+subject[\s\n]+to[\s\n]+having[\s\n]+all[\s\n]+their[\s\n]+activities[\s\n]+on[\s\n]+this[\s\n]+system[\s\n]*monitored[\s\n]+and[\s\n]+recorded[\s\n]+by[\s\n]+system[\s\n]+personnel.[\s\n]+Anyone[\s\n]+using[\s\n]+this[\s\n]*system[\s\n]+expressly[\s\n]+consents[\s\n]+to[\s\n]+such[\s\n]+monitoring[\s\n]+and[\s\n]+is[\s\n]+advised[\s\n]+that[\s\n]*if[\s\n]+such[\s\n]+monitoring[\s\n]+reveals[\s\n]+possible[\s\n]+evidence[\s\n]+of[\s\n]+criminal[\s\n]+activity[\s\n]*system[\s\n]+personal[\s\n]+may[\s\n]+provide[\s\n]+the[\s\n]+evidence[\s\n]+of[\s\n]+such[\s\n]+monitoring[\s\n]+to[\s\n]+law[\s\n]*enforcement[\s\n]+officials."

    # 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 34 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 15 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:

Sending ICMP redirects permits the system to instruct other systems to update their routing information. The ability to send ICMP redirects is only appropriate for systems acting as routers.

Severity: medium

References: AC-4, CM-7, SC-5, SC-7, 1551

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:

Sending ICMP redirects permits the system to instruct other systems to update their routing information. The ability to send ICMP redirects is only appropriate for systems acting as routers.

Severity: medium

References: CM-7, SC-5(1), 1551

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:

IP forwarding permits the kernel to forward packets from one network interface to another. The ability to forward packets between two networks is only appropriate for systems acting as routers.

Severity: medium

References: CM-7, SC-5, 366

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 12 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:

Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required.

Severity: medium

References: CM-7, SC-5, 1551

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:

Accepting ICMP redirects has few legitimate uses. It should be disabled unless it is absolutely required.

Severity: medium

References: CM-7, SC-5, 1503, 1551

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 Secure Redirects for All Interfaces [ref]rule

To set the runtime status of the `net.ipv4.conf.all.secure_redirects` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.conf.all.secure_redirects=0

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

    net.ipv4.conf.all.secure_redirects = 0

Rationale:

Accepting "secure" ICMP redirects (from those gateways listed as default gateways) has few legitimate uses. It should be disabled unless it is absolutely required.

Severity: medium

References: AC-4, CM-7, SC-5, 1503, 1551

Remediation Shell script: (show)

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

    sysctl_net_ipv4_conf_all_secure_redirects_value="1"

    #
    # Set runtime for net.ipv4.conf.all.secure_redirects
    #
    /sbin/sysctl -q -n -w net.ipv4.conf.all.secure_redirects=$sysctl_net_ipv4_conf_all_secure_redirects_value

    #
    # If net.ipv4.conf.all.secure_redirects present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.conf.all.secure_redirects = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.conf.all.secure_redirects /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.conf.all.secure_redirects.*/net.ipv4.conf.all.secure_redirects = $sysctl_net_ipv4_conf_all_secure_redirects_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.conf.all.secure_redirects to $sysctl_net_ipv4_conf_all_secure_redirects_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.conf.all.secure_redirects = $sysctl_net_ipv4_conf_all_secure_redirects_value" >> /etc/sysctl.conf
    fi

#### Configure Kernel Parameter to Log Martian Packets [ref]rule

To set the runtime status of the `net.ipv4.conf.all.log_martians` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.conf.all.log_martians=1

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

    net.ipv4.conf.all.log_martians = 1

Rationale:

The presence of "martian" packets (which have impossible addresses) as well as spoofed packets, source-routed packets, and redirects could be a sign of nefarious network activity. Logging these packets enables this activity to be detected.

Severity: low

References: AC-3(10), CM-7, SC-5(3), 126

Remediation Shell script: (show)

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

    sysctl_net_ipv4_conf_all_log_martians_value="1"

    #
    # Set runtime for net.ipv4.conf.all.log_martians
    #
    /sbin/sysctl -q -n -w net.ipv4.conf.all.log_martians=$sysctl_net_ipv4_conf_all_log_martians_value

    #
    # If net.ipv4.conf.all.log_martians present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.conf.all.log_martians = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.conf.all.log_martians /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.conf.all.log_martians.*/net.ipv4.conf.all.log_martians = $sysctl_net_ipv4_conf_all_log_martians_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.conf.all.log_martians to $sysctl_net_ipv4_conf_all_log_martians_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.conf.all.log_martians = $sysctl_net_ipv4_conf_all_log_martians_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:

Accepting source-routed packets in the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required.

Severity: medium

References: AC-4, CM-7, SC-5, SC-7, 1551

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:

This feature of the IPv4 protocol has few legitimate uses. It should be disabled unless it is absolutely required.

Severity: low

References: AC-4, CM-7, SC-5, SC-7, 1551

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 for Accepting Secure Redirects By Default [ref]rule

To set the runtime status of the `net.ipv4.conf.default.secure_redirects` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.conf.default.secure_redirects=0

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

    net.ipv4.conf.default.secure_redirects = 0

Rationale:

Accepting "secure" ICMP redirects (from those gateways listed as default gateways) has few legitimate uses. It should be disabled unless it is absolutely required.

Severity: medium

References: AC-4, CM-7, SC-5, SC-7, 1551

Remediation Shell script: (show)

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

    sysctl_net_ipv4_conf_default_secure_redirects_value="1"

    #
    # Set runtime for net.ipv4.conf.default.secure_redirects
    #
    /sbin/sysctl -q -n -w net.ipv4.conf.default.secure_redirects=$sysctl_net_ipv4_conf_default_secure_redirects_value

    #
    # If net.ipv4.conf.default.secure_redirects present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.conf.default.secure_redirects = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.conf.default.secure_redirects /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.conf.default.secure_redirects.*/net.ipv4.conf.default.secure_redirects = $sysctl_net_ipv4_conf_default_secure_redirects_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.conf.default.secure_redirects to $sysctl_net_ipv4_conf_default_secure_redirects_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.conf.default.secure_redirects = $sysctl_net_ipv4_conf_default_secure_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:

Ignoring ICMP echo requests (pings) sent to broadcast or multicast addresses makes the system slightly more difficult to enumerate on the network.

Severity: low

References: CM-7, SC-5, 1551

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 Ignore Bogus ICMP Error Responses [ref]rule

To set the runtime status of the `net.ipv4.icmp_ignore_bogus_error_responses` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.icmp_ignore_bogus_error_responses=1

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

    net.ipv4.icmp_ignore_bogus_error_responses = 1

Rationale:

Ignoring bogus ICMP error responses reduces log size, although some activity would not be logged.

Severity: low

References: CM-7, SC-5

Remediation Shell script: (show)

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

    sysctl_net_ipv4_icmp_ignore_bogus_error_responses_value="1"

    #
    # Set runtime for net.ipv4.icmp_ignore_bogus_error_responses
    #
    /sbin/sysctl -q -n -w net.ipv4.icmp_ignore_bogus_error_responses=$sysctl_net_ipv4_icmp_ignore_bogus_error_responses_value

    #
    # If net.ipv4.icmp_ignore_bogus_error_responses present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.icmp_ignore_bogus_error_responses = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.icmp_ignore_bogus_error_responses /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.icmp_ignore_bogus_error_responses.*/net.ipv4.icmp_ignore_bogus_error_responses = $sysctl_net_ipv4_icmp_ignore_bogus_error_responses_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.icmp_ignore_bogus_error_responses to $sysctl_net_ipv4_icmp_ignore_bogus_error_responses_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.icmp_ignore_bogus_error_responses = $sysctl_net_ipv4_icmp_ignore_bogus_error_responses_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

References: AC-4, SC-5(2), SC-5(3), 1092, 1095

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

#### Configure Kernel Parameter to Use Reverse Path Filtering for All Interfaces [ref]rule

To set the runtime status of the `net.ipv4.conf.all.rp_filter` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.conf.all.rp_filter=1

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

    net.ipv4.conf.all.rp_filter = 1

Rationale:

Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks.

Severity: medium

References: AC-4, SC-5, SC-7, 1551

Remediation Shell script: (show)

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

    sysctl_net_ipv4_conf_all_rp_filter_value="1"

    #
    # Set runtime for net.ipv4.conf.all.rp_filter
    #
    /sbin/sysctl -q -n -w net.ipv4.conf.all.rp_filter=$sysctl_net_ipv4_conf_all_rp_filter_value

    #
    # If net.ipv4.conf.all.rp_filter present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.conf.all.rp_filter = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.conf.all.rp_filter /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.conf.all.rp_filter.*/net.ipv4.conf.all.rp_filter = $sysctl_net_ipv4_conf_all_rp_filter_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.conf.all.rp_filter to $sysctl_net_ipv4_conf_all_rp_filter_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.conf.all.rp_filter = $sysctl_net_ipv4_conf_all_rp_filter_value" >> /etc/sysctl.conf
    fi

#### Configure Kernel Parameter to Use Reverse Path Filtering by Default [ref]rule

To set the runtime status of the `net.ipv4.conf.default.rp_filter` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv4.conf.default.rp_filter=1

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

    net.ipv4.conf.default.rp_filter = 1

Rationale:

Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface they were received on. It should not be used on systems which are routers for complicated networks, but is helpful for end hosts and routers serving small networks.

Severity: medium

References: AC-4, SC-5, SC-7

Remediation Shell script: (show)

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

    sysctl_net_ipv4_conf_default_rp_filter_value="1"

    #
    # Set runtime for net.ipv4.conf.default.rp_filter
    #
    /sbin/sysctl -q -n -w net.ipv4.conf.default.rp_filter=$sysctl_net_ipv4_conf_default_rp_filter_value

    #
    # If net.ipv4.conf.default.rp_filter present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv4.conf.default.rp_filter = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv4.conf.default.rp_filter /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv4.conf.default.rp_filter.*/net.ipv4.conf.default.rp_filter = $sysctl_net_ipv4_conf_default_rp_filter_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv4.conf.default.rp_filter to $sysctl_net_ipv4_conf_default_rp_filter_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv4.conf.default.rp_filter = $sysctl_net_ipv4_conf_default_rp_filter_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

References: 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

References: AC-18(a), AC-18(d), AC-18(3), CM-7, 85

#### Disable Bluetooth Service [ref]rule

The `bluetooth` service can be disabled with the following command:

    $ sudo chkconfig bluetooth off

    $ 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

References: 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

    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 bluetooth

Remediation Ansible snippet: (show)

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

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

#### 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

References: 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 4 rules

### Disable Support for IPv6 Unless Needed [ref]group

Despite configuration that suggests support for IPv6 has been disabled, link-local IPv6 address auto-configuration occurs even when only an IPv4 address is assigned. The only way to effectively prevent execution of the IPv6 networking stack is to instruct the system not to activate the IPv6 kernel module.

contains 2 rules

#### Disable IPv6 Networking Support Automatic Loading [ref]rule

To prevent the IPv6 kernel module (`ipv6`) from binding to the IPv6 networking stack, add the following line to `/etc/modprobe.d/disabled.conf` (or another file in `/etc/modprobe.d`):

    options ipv6 disable=1

This permits the IPv6 module to be loaded (and thus satisfy other modules that depend on it), while disabling support for the IPv6 protocol. Rationale:

Any unnecessary network stacks - including IPv6 - should be disabled, to reduce the vulnerability to exploitation.

Severity: medium

References: CM-7, 1551

Remediation Shell script: (show)

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

    # Prevent the IPv6 kernel module (ipv6) from loading the IPv6 networking stack
    echo "options ipv6 disable=1" > /etc/modprobe.d/ipv6.conf

    # Since according to: https://access.redhat.com/solutions/72733
    # "ipv6 disable=1" options doesn't always disable the IPv6 networking stack from
    # loading, instruct also sysctl configuration to disable IPv6 according to:
    # https://access.redhat.com/solutions/8709#rhel6disable

    declare -a IPV6_SETTINGS=("net.ipv6.conf.all.disable_ipv6" "net.ipv6.conf.default.disable_ipv6")

    for setting in ${IPV6_SETTINGS[@]}
    do
    	# Set runtime =1 for setting
    	/sbin/sysctl -q -n -w "$setting=1"

    	# If setting is present in /etc/sysctl.conf, change value to "1"
    	# else, add "$setting = 1" to /etc/sysctl.conf
    	if grep -q ^"$setting" /etc/sysctl.conf ; then
    		sed -i "s/^$setting.*/$setting = 1/g" /etc/sysctl.conf
    	else
    		echo "" >> /etc/sysctl.conf
    		echo "# Set $setting = 1 per security requirements" >> /etc/sysctl.conf
    		echo "$setting = 1" >> /etc/sysctl.conf
    	fi
    done

#### Disable Support for RPC IPv6 [ref]rule

RPC services for NFSv4 try to load transport modules for `udp6` and `tcp6` by default, even if IPv6 has been disabled in `/etc/modprobe.d`. To prevent RPC services such as `rpc.mountd` from attempting to start IPv6 network listeners, remove or comment out the following two lines in `/etc/netconfig`:

    udp6       tpi_clts      v     inet6    udp     -       -
    tcp6       tpi_cots_ord  v     inet6    tcp     -       -

Severity: low

References: CM-7

Remediation Shell script: (show)

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

    # Drop 'tcp6' and 'udp6' entries from /etc/netconfig to prevent RPC
    # services for NFSv4 from attempting to start IPv6 network listeners
    declare -a IPV6_RPC_ENTRIES=("tcp6" "udp6")

    for rpc_entry in ${IPV6_RPC_ENTRIES[@]}
    do
    	sed -i "/^$rpc_entry[[:space:]]\+tpi\_.*inet6.*/d" /etc/netconfig
    done

### 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 2 rules

### 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 2 rules

#### Configure Accepting IPv6 Router Advertisements [ref]rule

To set the runtime status of the `net.ipv6.conf.default.accept_ra` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv6.conf.default.accept_ra=0

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

    net.ipv6.conf.default.accept_ra = 0

Rationale:

An illicit router advertisement message could result in a man-in-the-middle attack.

Severity: low

References: CM-7, 4.4.1.1

Remediation Shell script: (show)

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

    sysctl_net_ipv6_conf_default_accept_ra_value="0"

    #
    # Set runtime for net.ipv6.conf.default.accept_ra
    #
    /sbin/sysctl -q -n -w net.ipv6.conf.default.accept_ra=$sysctl_net_ipv6_conf_default_accept_ra_value

    #
    # If net.ipv6.conf.default.accept_ra present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv6.conf.default.accept_ra = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv6.conf.default.accept_ra /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv6.conf.default.accept_ra.*/net.ipv6.conf.default.accept_ra = $sysctl_net_ipv6_conf_default_accept_ra_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv6.conf.default.accept_ra to $sysctl_net_ipv6_conf_default_accept_ra_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv6.conf.default.accept_ra = $sysctl_net_ipv6_conf_default_accept_ra_value" >> /etc/sysctl.conf
    fi

#### Configure Accepting IPv6 Redirects By Default [ref]rule

To set the runtime status of the `net.ipv6.conf.default.accept_redirects` kernel parameter, run the following command:

    $ sudo sysctl -w net.ipv6.conf.default.accept_redirects=0

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

    net.ipv6.conf.default.accept_redirects = 0

Rationale:

An illicit ICMP redirect message could result in a man-in-the-middle attack.

Severity: medium

References: CM-7, 1551, 4.4.1.2

Remediation Shell script: (show)

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

    sysctl_net_ipv6_conf_default_accept_redirects_value="0"

    #
    # Set runtime for net.ipv6.conf.default.accept_redirects
    #
    /sbin/sysctl -q -n -w net.ipv6.conf.default.accept_redirects=$sysctl_net_ipv6_conf_default_accept_redirects_value

    #
    # If net.ipv6.conf.default.accept_redirects present in /etc/sysctl.conf, change value to appropriate value
    #	else, add "net.ipv6.conf.default.accept_redirects = value" to /etc/sysctl.conf
    #
    if grep --silent ^net.ipv6.conf.default.accept_redirects /etc/sysctl.conf ; then
    	sed -i "s/^net.ipv6.conf.default.accept_redirects.*/net.ipv6.conf.default.accept_redirects = $sysctl_net_ipv6_conf_default_accept_redirects_value/g" /etc/sysctl.conf
    else
    	echo -e "\n# Set net.ipv6.conf.default.accept_redirects to $sysctl_net_ipv6_conf_default_accept_redirects_value per security requirements" >> /etc/sysctl.conf
    	echo "net.ipv6.conf.default.accept_redirects = $sysctl_net_ipv6_conf_default_accept_redirects_value" >> /etc/sysctl.conf
    fi

### iptables and ip6tables [ref]group

A host-based firewall called `netfilter` is included as part of the Linux kernel distributed with the system. It is activated by default. This firewall is controlled by the program `iptables`, and the entire capability is frequently referred to by this name. An analogous program called `ip6tables` handles filtering for IPv6.
Unlike TCP Wrappers, which depends on the network server program to support and respect the rules written, `netfilter` filtering occurs at the kernel level, before a program can even process the data from the network packet. As such, any program on the system is affected by the rules written.
This section provides basic information about strengthening the `iptables` and `ip6tables` configurations included with the system. For more complete information that may allow the construction of a sophisticated ruleset tailored to your environment, please consult the references at the end of this section.

contains 5 rules

### Inspect and Activate Default Rules [ref]group

View the currently-enforced `iptables` rules by running the command:

    $ sudo iptables -nL --line-numbers

The command is analogous for `ip6tables`.
If the firewall does not appear to be active (i.e., no rules appear), activate it and ensure that it starts at boot by issuing the following commands (and analogously for `ip6tables`):

    $ sudo service iptables restart

The default iptables rules are:

    Chain INPUT (policy ACCEPT)
    num  target     prot opt source       destination
    1    ACCEPT     all  --  0.0.0.0/0    0.0.0.0/0    state RELATED,ESTABLISHED
    2    ACCEPT     icmp --  0.0.0.0/0    0.0.0.0/0
    3    ACCEPT     all  --  0.0.0.0/0    0.0.0.0/0
    4    ACCEPT     tcp  --  0.0.0.0/0    0.0.0.0/0    state NEW tcp dpt:22
    5    REJECT     all  --  0.0.0.0/0    0.0.0.0/0    reject-with icmp-host-prohibited

    Chain FORWARD (policy ACCEPT)
    num  target     prot opt source       destination
    1    REJECT     all  --  0.0.0.0/0    0.0.0.0/0    reject-with icmp-host-prohibited

    Chain OUTPUT (policy ACCEPT)
    num  target     prot opt source       destination

The `ip6tables` default rules are essentially the same.

contains 3 rules

#### Verify ip6tables Enabled if Using IPv6 [ref]rule

The `ip6tables` service can be enabled with the following command:

    $ sudo chkconfig --level 2345 ip6tables on

Rationale:

The `ip6tables` service provides the system's host-based firewalling capability for IPv6 and ICMPv6.

Severity: medium

References: AC-4, CA-3(c), CM-7, 32, 66, 1115, 1118, 1092, 1117, 1098, 1100, 1097, 1414

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 ip6tables

Remediation Ansible snippet: (show)

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

    - name: Enable service ip6tables
      service:
        name="{{item}}"
        enabled="yes"
        state="started"
      with_items:
        - ip6tables

#### Set Default ip6tables Policy for Incoming Packets [ref]rule

To set the default policy to DROP (instead of ACCEPT) for the built-in INPUT chain which processes incoming packets, add or correct the following line in `/etc/sysconfig/ip6tables`:

    :INPUT DROP [0:0]

If changes were required, reload the ip6tables rules:

    $ sudo service ip6tables reload

Rationale:

In `ip6tables`, the default policy is applied only after all the applicable rules in the table are examined for a match. Setting the default policy to `DROP` implements proper design for a firewall, i.e. any packets which are not explicitly permitted should not be accepted.

Severity: medium

References: CM-7, 66

Remediation Shell script: (show)

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

    sed -i 's/^:INPUT ACCEPT.*/:INPUT DROP [0:0]/g' /etc/sysconfig/ip6tables

#### Verify iptables Enabled [ref]rule

The `iptables` service can be enabled with the following command:

    $ sudo chkconfig --level 2345 iptables on

Rationale:

The `iptables` service provides the system's host-based firewalling capability for IPv4 and ICMP.

Severity: medium

References: AC-4, CA-3(c), CM-7, 32, 66, 1115, 1118, 1092, 1117, 1098, 1100, 1097, 1414

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 iptables

Remediation Ansible snippet: (show)

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

    - name: Enable service iptables
      service:
        name="{{item}}"
        enabled="yes"
        state="started"
      with_items:
        - iptables

### 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 the configuration files `iptables` and `ip6tables` in the directory `/etc/sysconfig`. Many of the lines in these files are similar to the command line arguments that would be provided to the programs `/sbin/iptables` or `/sbin/ip6tables` - but some are quite different.
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 iptables program to load in rules, and then invokes service iptables save to write those loaded rules to `/etc/sysconfig/iptables.`
The following alterations can be made directly to `/etc/sysconfig/iptables` and `/etc/sysconfig/ip6tables`. Instructions apply to both unless otherwise noted. Language and address conventions for regular iptables are used throughout this section; configuration for ip6tables will be either analogous or explicitly covered.

Warning: The program `system-config-securitylevel` allows additional services to penetrate the default firewall rules and automatically adjusts `/etc/sysconfig/iptables`. This program is only useful if the default ruleset meets your security requirements. Otherwise, this program should not be used to make changes to the firewall configuration because it re-writes the saved configuration file.

contains 2 rules

#### Set Default iptables Policy for Incoming Packets [ref]rule

To set the default policy to DROP (instead of ACCEPT) for the built-in INPUT chain which processes incoming packets, add or correct the following line in `/etc/sysconfig/iptables`:

    :INPUT DROP [0:0]

Rationale:

In `iptables` the default policy is applied only after all the applicable rules in the table are examined for a match. Setting the default policy to `DROP` implements proper design for a firewall, i.e. any packets which are not explicitly permitted should not be accepted.

Severity: medium

References: CM-7, 66, 1109, 1154, 1414

Remediation Shell script: (show)

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

    sed -i 's/^:INPUT ACCEPT.*/:INPUT DROP [0:0]/g' /etc/sysconfig/iptables

#### Set Default iptables Policy for Forwarded Packets [ref]rule

To set the default policy to DROP (instead of ACCEPT) for the built-in FORWARD chain which processes packets that will be forwarded from one interface to another, add or correct the following line in `/etc/sysconfig/iptables`:

    :FORWARD DROP [0:0]

Rationale:

In `iptables`, the default policy is applied only after all the applicable rules in the table are examined for a match. Setting the default policy to `DROP` implements proper design for a firewall, i.e. any packets which are not explicitly permitted should not be accepted.

Severity: medium

References: CM-7, 1109

Remediation Shell script: (show)

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

    sed -i 's/^:FORWARD ACCEPT.*/:FORWARD DROP [0:0]/g' /etc/sysconfig/iptables

### Uncommon Network Protocols [ref]group

The system includes support for several network protocols which are not commonly used. Although security vulnerabilities in kernel networking code are not frequently discovered, the consequences can be dramatic. Ensuring uncommon network protocols are disabled reduces the system's risk to attacks targeted at its implementation of those protocols.

Warning: Although these protocols are not commonly used, avoid disruption in your network environment by ensuring they are not needed prior to disabling them.

contains 4 rules

#### Disable DCCP Support [ref]rule

The Datagram Congestion Control Protocol (DCCP) is a relatively new transport layer protocol, designed to support streaming media and telephony. To configure the system to prevent the `dccp` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install dccp /bin/true

Rationale:

Disabling DCCP protects the system against exploitation of any flaws in its implementation.

Severity: medium

References: CM-7, 382

Remediation Shell script: (show)

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

    echo "install dccp /bin/true" > /etc/modprobe.d/dccp.conf

Remediation Ansible snippet: (show)

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

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

#### Disable SCTP Support [ref]rule

The Stream Control Transmission Protocol (SCTP) is a transport layer protocol, designed to support the idea of message-oriented communication, with several streams of messages within one connection. To configure the system to prevent the `sctp` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install sctp /bin/true

Rationale:

Disabling SCTP protects the system against exploitation of any flaws in its implementation.

Severity: medium

References: CM-7, 382

Remediation Shell script: (show)

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

    echo "install sctp /bin/true" > /etc/modprobe.d/sctp.conf

Remediation Ansible snippet: (show)

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

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

#### Disable RDS Support [ref]rule

The Reliable Datagram Sockets (RDS) protocol is a transport layer protocol designed to provide reliable high- bandwidth, low-latency communications between nodes in a cluster. To configure the system to prevent the `rds` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install rds /bin/true

Rationale:

Disabling RDS protects the system against exploitation of any flaws in its implementation.

Severity: low

References: CM-7, 382

Remediation Shell script: (show)

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

    echo "install rds /bin/true" > /etc/modprobe.d/rds.conf

Remediation Ansible snippet: (show)

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

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

#### Disable TIPC Support [ref]rule

The Transparent Inter-Process Communication (TIPC) protocol is designed to provide communications between nodes in a cluster. To configure the system to prevent the `tipc` kernel module from being loaded, add the following line to a file in the directory `/etc/modprobe.d`:

    install tipc /bin/true

Rationale:

Disabling TIPC protects the system against exploitation of any flaws in its implementation.

Severity: medium

References: CM-7, 382

Remediation Shell script: (show)

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

    echo "install tipc /bin/true" > /etc/modprobe.d/tipc.conf

Remediation Ansible snippet: (show)

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

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

#### Disable Zeroconf Networking [ref]rule

Zeroconf networking allows the system to assign itself an IP address and engage in IP communication without a statically-assigned address or even a DHCP server. Automatic address assignment via Zeroconf (or DHCP) is not recommended. To disable Zeroconf automatic route assignment in the 169.254.0.0 subnet, add or correct the following line in `/etc/sysconfig/network`:

    NOZEROCONF=yes

Rationale:

Zeroconf addresses are in the network 169.254.0.0. The networking scripts add entries to the system's routing table for these addresses. Zeroconf address assignment commonly occurs when the system is configured to use DHCP but fails to receive an address assignment from the DHCP server.

Severity: low

References: CM-7

Remediation Shell script: (show)

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

    echo "NOZEROCONF=yes" >> /etc/sysconfig/network

#### 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:

If any results are returned, then a sniffing process (such as tcpdump or Wireshark) is likely to be using the interface and this should be investigated.

Severity: low

References: CM-7, MA-3

### 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 6, 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 7 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 6 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 3 rules

#### Ensure Log Files Are Owned By Appropriate User [ref]rule

The owner of all log files written by `rsyslog` should be root. These log files are determined by the second part of each Rule line in `/etc/rsyslog.conf` and typically all appear in `/var/log`. For each log file LOGFILE referenced in `/etc/rsyslog.conf`, run the following command to inspect the file's owner:

    $ ls -l LOGFILE

If the owner is not `root`, run the following command to correct this:

    $ sudo chown root LOGFILE

Rationale:

The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.

Severity: medium

References: AC-6, SI-11, 1314

#### Ensure Log Files Are Owned By Appropriate Group [ref]rule

The group-owner of all log files written by `rsyslog` should be root. These log files are determined by the second part of each Rule line in `/etc/rsyslog.conf` and typically all appear in `/var/log`. For each log file LOGFILE referenced in `/etc/rsyslog.conf`, run the following command to inspect the file's group owner:

    $ ls -l LOGFILE

If the owner is not `root`, run the following command to correct this:

    $ sudo chgrp root LOGFILE

Rationale:

The log files generated by rsyslog contain valuable information regarding system configuration, user authentication, and other such information. Log files should be protected from unauthorized access.

Severity: medium

References: AC-6, SI-11, 1314

#### Ensure System Log Files Have Correct Permissions [ref]rule

The file permissions for all log files written by `rsyslog` should be set to 600, or more restrictive. These log files are determined by the second part of each Rule line in `/etc/rsyslog.conf` and typically all appear in `/var/log`. For each log file LOGFILE referenced in `/etc/rsyslog.conf`, run the following command to inspect the file's permissions:

    $ ls -l LOGFILE

If the permissions are not 600 or more restrictive, run the following command to correct this:

    $ sudo chmod 0600 LOGFILE

Rationale:

Log files can contain valuable information regarding system configuration. If the system log files are not protected unauthorized users could change the logged data, eliminating their forensic value.

Severity: medium

References: SI-11, 1314

Remediation Shell script: (show)

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

    # List of log file paths to be inspected for correct permissions
    # * Primarily inspect log file paths listed in /etc/rsyslog.conf
    RSYSLOG_ETC_CONFIG="/etc/rsyslog.conf"
    # * And also the log file paths listed after rsyslog's $IncludeConfig directive
    #   (store the result into array for the case there's shell glob used as value of IncludeConfig)
    RSYSLOG_INCLUDE_CONFIG=($(grep -e "\$IncludeConfig[[:space:]]\+[^[:space:];]\+" /etc/rsyslog.conf | cut -d ' ' -f 2))
    # Declare an array to hold the final list of different log file paths
    declare -a LOG_FILE_PATHS

    # Browse each file selected above as containing paths of log files
    # ('/etc/rsyslog.conf' and '/etc/rsyslog.d/*.conf' in the default configuration)
    for LOG_FILE in "${RSYSLOG_ETC_CONFIG}" "${RSYSLOG_INCLUDE_CONFIG[@]}"
    do
    	# From each of these files extract just particular log file path(s), thus:
    	# * Ignore lines starting with space (' '), comment ('#"), or variable syntax ('$') characters,
    	# * Ignore empty lines,
    	# * From the remaining valid rows select only fields constituting a log file path
    	# Text file column is understood to represent a log file path if and only if all of the following are met:
    	# * it contains at least one slash '/' character,
    	# * it doesn't contain space (' '), colon (':'), and semicolon (';') characters
    	# Search log file for path(s) only in case it exists!
    	if [[ -f "${LOG_FILE}" ]]
    	then
    		MATCHED_ITEMS=$(sed -e "/^[[:space:]|#|$]/d ; s/[^\/]*[[:space:]]*\([^:;[:space:]]*\)/\1/g ; /^$/d" "${LOG_FILE}")
    		# Since above sed command might return more than one item (delimited by newline), split the particular
    		# matches entries into new array specific for this log file
    		readarray -t ARRAY_FOR_LOG_FILE <<< "$MATCHED_ITEMS"
    		# Concatenate the two arrays - previous content of $LOG_FILE_PATHS array with
    		# items from newly created array for this log file
    		LOG_FILE_PATHS=("${LOG_FILE_PATHS[@]}" "${ARRAY_FOR_LOG_FILE[@]}")
    		# Delete the temporary array
    		unset ARRAY_FOR_LOG_FILE
    	fi
    done

    for PATH in "${LOG_FILE_PATHS[@]}"
    do
    	# Sanity check - if particular $PATH is empty string, skip it from further processing
    	if [ -z "$PATH" ]
    	then
    		continue
    	fi
    	# Per https://access.redhat.com/solutions/66805 '/var/log/boot.log' log file needs special care => perform it
    	if [ "$PATH" == "/var/log/boot.log" ]
    	then
    		# Ensure permissions of /var/log/boot.log are configured to be updated in /etc/rc.local
    		if ! /bin/grep -q "boot.log" "/etc/rc.local"
    		then
    			echo "/bin/chmod 600 /var/log/boot.log" >> /etc/rc.local
    		fi
    		# Ensure /etc/rc.d/rc.local has user-executable permission
    		# (in order to be actually executed during boot)
    		if [ "$(/usr/bin/stat -c %a /etc/rc.d/rc.local)" -ne 744 ]
    		then
    			/bin/chmod u+x /etc/rc.d/rc.local
    		fi
    	fi
    	# Also for each log file check if its permissions differ from 600. If so, correct them
    	if [ "$(/usr/bin/stat -c %a "$PATH")" -ne 600 ]
    	then
    		/bin/chmod 600 "$PATH"
    	fi
    done

### 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

References: AU-3(2), AU-9, 1348, 136

### Ensure All Logs are Rotated by logrotate [ref]group

Edit the file `/etc/logrotate.d/syslog`. Find the first line, which should look like this (wrapped for clarity):

    /var/log/messages /var/log/secure /var/log/maillog /var/log/spooler \
      /var/log/boot.log /var/log/cron {

Edit this line so that it contains a one-space-separated listing of each log file referenced in `/etc/rsyslog.conf`.
All logs in use on a system must be rotated regularly, or the log files will consume disk space over time, eventually interfering with system operation. The file `/etc/logrotate.d/syslog` is the configuration file used by the `logrotate` program to maintain all log files written by `syslog`. By default, it rotates logs weekly and stores four archival copies of each log. These settings can be modified by editing `/etc/logrotate.conf`, but the defaults are sufficient for purposes of this guide.
Note that `logrotate` is run nightly by the cron job `/etc/cron.daily/logrotate`. If particularly active logs need to be rotated more often than once a day, some other mechanism must be used.

contains 1 rule

#### Ensure Logrotate Runs Periodically [ref]rule

The `logrotate` utility allows for the automatic rotation of log files. The frequency of rotation is specified in `/etc/logrotate.conf`, which triggers a cron task. To configure logrotate to run daily, add or correct the following line in `/etc/logrotate.conf`:

    # rotate log files frequency
    daily

Rationale:

Log files that are not properly rotated run the risk of growing so large that they fill up the /var/log partition. Valuable logging information could be lost if the /var/log partition becomes full.

Severity: low

References: AU-9, 366

#### Ensure rsyslog is Installed [ref]rule

Rsyslog is installed by default. The `rsyslog` package can be installed with the following command:

    $ sudo yum install rsyslog

Rationale:

The rsyslog package provides the rsyslog daemon, which provides system logging services.

Severity: medium

References: AU-9(2), 1311, 1312

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 rsyslog

Remediation Ansible snippet: (show)

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

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

Remediation Puppet snippet: (show)

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

    include install_rsyslog

    class install_rsyslog {
      package { 'rsyslog':
        ensure => 'installed',
      }
    }

Remediation Anaconda snippet: (show)

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

    package --add=rsyslog

#### Enable rsyslog Service [ref]rule

The `rsyslog` service provides syslog-style logging by default on Red Hat Enterprise Linux 6. The `rsyslog` service can be enabled with the following command:

    $ sudo chkconfig --level 2345 rsyslog on

Rationale:

The `rsyslog` service must be running in order to provide logging services, which are essential to system administration.

Severity: medium

References: AU-12, 1557, 1312, 1311

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 rsyslog

Remediation Ansible snippet: (show)

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

    - name: Enable service rsyslog
      service:
        name="{{item}}"
        enabled="yes"
        state="started"
      with_items:
        - rsyslog

### 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.
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 `http://docs.fedoraproject.org/en-US/Fedora/13/html/Security-Enhanced_Linux/sect-Security-Enhanced_Linux-Fixing_Problems-Raw_Audit_Messages.html` 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 7 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

References: AU-1(b), AU-11, IR-5

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

References: AU-1(b), AU-11, IR-5

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

References: AU-1(b), AU-4, AU-11, IR-5

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

References: AU-1(b), AU-4, AU-5(b), IR-5, 140, 143

Remediation Shell script: (show)

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

    var_auditd_space_left_action="email"

    #
    # If space_left_action present in /etc/audit/auditd.conf, change value
    # to var_auditd_space_left_action, else
    # add "space_left_action = $var_auditd_space_left_action" to /etc/audit/auditd.conf
    #

    if grep --silent ^space_left_action /etc/audit/auditd.conf ; then
            sed -i 's/^space_left_action.*/space_left_action = '"$var_auditd_space_left_action"'/g' /etc/audit/auditd.conf
    else
            echo -e "\n# Set space_left_action to $var_auditd_space_left_action per security requirements" >> /etc/audit/auditd.conf
            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

References: AU-1(b), AU-4, AU-5(b), IR-5, 140, 1343

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

References: AU-1(b), AU-4, AU-5(a), IR-5, 139, 144

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 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: low

References: AU-1(b), AU-3(2), IR-5, 136

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 32 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

On a 32-bit system, add the following to `/etc/audit/audit.rules`:

    # audit_time_rules
    -a always,exit -F arch=b32 -S adjtimex -k audit_time_rules

On a 64-bit system, add the following to `/etc/audit/audit.rules`:

    # audit_time_rules
    -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 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 rhel6_perform_audit_adjtimex_settimeofday_stime_remediation {

    # Perform the remediation for the 'adjtimex', 'settimeofday', and 'stime' audit
    # system calls on Red Hat Enterprise Linux 6 OS
    #
    # 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=${ARCH} -S adjtimex -S settimeofday -k audit_time_rules"
            fi
            # Perform the remediation itself
            fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

    }

    rhel6_perform_audit_adjtimex_settimeofday_stime_remediation

#### Record attempts to alter time through settimeofday [ref]rule

On a 32-bit system, add the following to `/etc/audit/audit.rules`:

    # audit_time_rules
    -a always,exit -F arch=b32 -S settimeofday -k audit_time_rules

On a 64-bit system, add the following to `/etc/audit/audit.rules`:

    # audit_time_rules
    -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 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 rhel6_perform_audit_adjtimex_settimeofday_stime_remediation {

    # Perform the remediation for the 'adjtimex', 'settimeofday', and 'stime' audit
    # system calls on Red Hat Enterprise Linux 6 OS
    #
    # 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=${ARCH} -S adjtimex -S settimeofday -k audit_time_rules"
            fi
            # Perform the remediation itself
            fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

    }

    rhel6_perform_audit_adjtimex_settimeofday_stime_remediation

#### Record Attempts to Alter Time Through stime [ref]rule

Add the following line to `/etc/audit/audit.rules` for both 32-bit and 64-bit systems:

    # audit_time_rules
    -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 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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 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 rhel6_perform_audit_adjtimex_settimeofday_stime_remediation {

    # Perform the remediation for the 'adjtimex', 'settimeofday', and 'stime' audit
    # system calls on Red Hat Enterprise Linux 6 OS
    #
    # 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=${ARCH} -S adjtimex -S settimeofday -k audit_time_rules"
            fi
            # Perform the remediation itself
            fix_audit_syscall_rule "auditctl" "$PATTERN" "$GROUP" "$ARCH" "$FULL_RULE"
    done

    }

    rhel6_perform_audit_adjtimex_settimeofday_stime_remediation

#### Record Attempts to Alter Time Through clock_settime [ref]rule

On a 32-bit system, add the following to `/etc/audit/audit.rules`:

    # time-change
    -a always,exit -F arch=b32 -S clock_settime -F a0=0x0 -F key=time-change

On a 64-bit system, add the following to `/etc/audit/audit.rules`:

    # time-change
    -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 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"

    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"
    done

#### Record Attempts to Alter the localtime File [ref]rule

Add the following to `/etc/audit/audit.rules`:

    -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 1487, 169

Remediation Shell script: (show)

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

    # Perform the remediation

    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"

### 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>=500 -F auid!=4294967295 -k perm_mod
        -a always,exit -F arch=b32 -S chown -S fchown -S fchownat -S lchown -F auid>=500 -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>=500 -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>=500 -F auid!=4294967295 -k perm_mod
        -a always,exit -F arch=b64 -S chown -S fchown -S fchownat -S lchown -F auid>=500 -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>=500 -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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S chmod -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S chmod  -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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>=500 -F auid!=4294967295 -k *"
    	GROUP="chmod"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S chmod -S fchmod -S fchmodat -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S chown -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S chown -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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>=500 -F auid!=4294967295 -k *"
    	GROUP="chown"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S chown -S fchown -S fchownat -S lchown -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S fchmod -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S fchmod -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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>=500 -F auid!=4294967295 -k *"
    	GROUP="chmod"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S chmod -S fchmod -S fchmodat -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S fchmodat -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S fchmodat -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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>=500 -F auid!=4294967295 -k *"
    	GROUP="chmod"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S chmod -S fchmod -S fchmodat -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S fchown -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S fchown -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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>=500 -F auid!=4294967295 -k *"
    	GROUP="chown"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S chown -S fchown -S fchownat -S lchown -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S fchownat -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S fchownat -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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>=500 -F auid!=4294967295 -k *"
    	GROUP="chown"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S chown -S fchown -S fchownat -S lchown -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S fremovexattr -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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 "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=500 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S fsetxattr -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S fsetxattr -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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 "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=500 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S lchown -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S lchown -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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>=500 -F auid!=4294967295 -k *"
    	GROUP="chown"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S chown -S fchown -S fchownat -S lchown -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S lremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S lremovexattr -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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 "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=500 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S lsetxattr -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S lsetxattr -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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 "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=500 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S removexattr -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S removexattr -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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 "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=500 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    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. Add the following to `/etc/audit/audit.rules`:

    -a always,exit -F arch=b32 -S setxattr -F auid>=500 -F auid!=4294967295 -k perm_mod

If the system is 64 bit then also add the following:

    -a always,exit -F arch=b64 -S setxattr -F auid>=500 -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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 "${RULE_ARCHS[@]}"
    do
    	PATTERN="-a always,exit .* -F auid>=500 -F auid!=4294967295 -k *"
    	GROUP="xattr"
    	FULL_RULE="-a always,exit -F arch=${ARCH} -S setxattr -S lsetxattr -S fsetxattr -S removexattr -S lremovexattr -S fremovexattr -F auid>=500 -F auid!=4294967295 -k perm_mod"

    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"
    done

#### Record Events that Modify User/Group Information [ref]rule

Add the following to `/etc/audit/audit.rules`, in order to capture events that modify account changes:

    # audit_rules_usergroup_modification
    -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

References: AC-2(4), AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 18, 1403, 1404, 1405, 1684, 1683, 1685, 1686

Remediation Shell script: (show)

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

    # Perform the remediation

    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 "auditctl" "/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 "auditctl" "/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"

#### Record Events that Modify the System's Network Environment [ref]rule

Add the following to `/etc/audit/audit.rules`, setting ARCH to either b32 or b64 as appropriate for your system:

    # audit_rules_networkconfig_modification
    -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5

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"

    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"
    done

    # Then perform the remediations for the watch rules

    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 "auditctl" "/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 "auditctl" "/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: low

References: AC-6, AU-1(b), AU-9, IR-5, 166

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

#### System Audit Logs Must Be Owned By Root [ref]rule

To properly set the owner of `/var/log`, run the command:

    $ sudo chown root /var/log

Rationale:

Failure to give ownership of the audit log files to root allows the designated owner, and unauthorized users, potential access to sensitive information.

Severity: low

References: AC-6, AU-1(b), AU-9, IR-5, 166

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
        chown root.${GROUP} /var/log/audit
        chown root.${GROUP} /var/log/audit/audit.log*
      else
        chown root.root /var/log/audit
        chown root.root /var/log/audit/audit.log*
      fi
    else
      chown root.root /var/log/audit
      chown root.root /var/log/audit/audit.log*
    fi

#### Record Events that Modify the System's Mandatory Access Controls [ref]rule

Add the following to `/etc/audit/audit.rules`:

    -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5

Remediation Shell script: (show)

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

    # Perform the remediation

    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"

#### Record Attempts to Alter Login and Logout Events [ref]rule

The audit system already collects login info for all users and root. To watch for attempted manual edits of files involved in storing login events, add the following to `/etc/audit/audit.rules`:

    -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: low

References: AC-3(10), AU-1(b), AU-12(a), AU-12(c), IR-5

Remediation Shell script: (show)

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

    # Perform the remediation

    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 "auditctl" "/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"

#### Record Attempts to Alter Process and Session Initiation Information [ref]rule

The audit system already collects process information for all users and root. To watch for attempted manual edits of files involved in storing such process information, add the following to `/etc/audit/audit.rules`:

    -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

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5

Remediation Shell script: (show)

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

    # Perform the remediation

    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 "auditctl" "/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"

#### 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. Add the following to `/etc/audit/audit.rules`:

    -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>=500 -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>=500 -F auid!=4294967295 -k access

If the system is 64 bit then also add the following:

    -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>=500 -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>=500 -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: low

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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>=500 -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>=500 -F auid!=4294967295 -k access"

    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"

    	# Then fix the -EPERM requirement
    	PATTERN="-a always,exit -F arch=$ARCH -S .* -F exit=-EPERM -F auid>=500 -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>=500 -F auid!=4294967295 -k access"

    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"

    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

Then, for each setuid / setgid program on the system, add a line of the following form to `/etc/audit/audit.rules`, where SETUID_PROG_PATH is the full path to each setuid / setgid program in the list:

    -a always,exit -F path=SETUID_PROG_PATH -F perm=x -F auid>=500 -F auid!=4294967295 -k privileged

Rationale:

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: low

References: AC-3(10)), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AC-6(9), AU-12(a), AU-12(c), IR-5, 40

Remediation Shell script: (show)

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

    # Perform the remediation

    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" "500"

#### 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. Add the following to `/etc/audit/audit.rules`, setting ARCH to either b32 or b64 as appropriate for your system:

    -a always,exit -F arch=ARCH -S mount -F auid>=500 -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: low

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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>=500 -F auid!=4294967295 -k *"
    	GROUP="mount"
    	FULL_RULE="-a always,exit -F arch=$ARCH -S mount -F auid>=500 -F auid!=4294967295 -k export"

    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"
    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. Add the following to `/etc/audit/audit.rules`, 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>=500 -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: low

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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>=500 -F auid!=4294967295 -k delete"
    	# 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>=500 -F auid!=4294967295 -k delete"

    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"
    done

#### Ensure auditd Collects System Administrator Actions [ref]rule

At a minimum the audit system should collect administrator actions for all users and root. Add the following to `/etc/audit/audit.rules`:

    -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

References: AC-2(7)(b), AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

Remediation Shell script: (show)

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

    # Perform the remediation

    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"

#### Ensure auditd Collects Information on Kernel Module Loading and Unloading [ref]rule

Add the following to `/etc/audit/audit.rules` in order to capture kernel module loading and unloading events, setting ARCH to either b32 or b64 as appropriate for your system:

    -w /sbin/insmod -p x -k modules
    -w /sbin/rmmod -p x -k modules
    -w /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: low

References: AC-3(10), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-12(a), AU-12(c), IR-5, 126

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"

    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"
    done

    # Then perform the remediations for the watch rules

    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" "/sbin/insmod" "x" "modules"
    fix_audit_watch_rule "auditctl" "/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" "/sbin/modprobe" "x" "modules"

#### Make the auditd Configuration Immutable [ref]rule

Add the following to `/etc/audit/audit.rules` in order to make the 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

References: AC-6, AU-1(b), AU-2(a), AU-2(c), AU-2(d), IR-5

Remediation Shell script: (show)

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

    readonly AUDIT_RULES='/etc/audit/audit.rules'

    # If '-e .*' setting present in audit.rules already, delete it since the
    # auditctl(8) manual page instructs it should be the last rule in configuration
    sed -i '/-e[[:space:]]\+.*/d' $AUDIT_RULES

    # Append '-e 2' requirement at the end of audit.rules
    echo '' >> $AUDIT_RULES
    echo '# Set the audit.rules configuration immutable per security requirements' >> $AUDIT_RULES
    echo '# Reboot is required to change audit rules once this setting is applied' >> $AUDIT_RULES
    echo '-e 2' >> $AUDIT_RULES

#### 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 chkconfig --level 2345 auditd on

Rationale:

Ensuring the `auditd` service is active ensures audit records generated by the kernel can be written to disk, or that appropriate actions will be taken if other obstacles exist.

Severity: medium

References: AC-17(1), AU-1(b), AU-10, AU-12(a), AU-12(c), IR-5, 347, 157, 172, 880, 1353, 1462, 1487, 1115, 1454, 067, 158, 831, 1190, 1312, 1263, 130, 120, 1589

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 kernel line in `/etc/grub.conf`, in the manner below:

    kernel /vmlinuz-version ro vga=ext root=/dev/VolGroup00/LogVol00 rhgb quiet audit=1

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: low

References: AC-17(1), AU-14(1), AU-1(b), AU-2(a), AU-2(c), AU-2(d), AU-10, IR-5, 169

Remediation Shell script: (show)

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

    /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 6 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 6 system and provides guidance about which ones can be safely disabled.
Red Hat Enterprise Linux 6 provides a convenient minimal install option that essentially installs the bare necessities for a functional system. When building Red Hat Enterprise Linux 6 systems, it is highly recommended to select the minimal packages and then build up the system from there.

contains 76 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 6 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 `iptables` to restrict access to the vulnerable service to only those remote hosts which have a known need to use it.

contains 16 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 6.

contains 2 rules

#### Disable xinetd Service [ref]rule

The `xinetd` service can be disabled with the following command:

    $ sudo chkconfig xinetd off

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

References: 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

References: CM-7, 305

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 2 rules

#### Disable telnet Service [ref]rule

The `telnet` service can be disabled with the following command:

    $ sudo chkconfig telnet off

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

References: CM-7, IA-5(1)(c), 68, 1436, 197, 877, 888

#### Uninstall telnet-server Package [ref]rule

The `telnet-server` package can be uninstalled with the following command:

    $ sudo yum erase telnet-server

Rationale:

Removing the `telnet-server` package decreases the risk of the telnet service's accidental (or intentional) activation.

Severity: high

References: CM-7, 305, 381

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

### 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` package provides several obsolete and insecure network services. Removing it decreases the risk of those services' accidental (or intentional) activation.

Severity: high

References: CM-7, 305, 381

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, should be disabled. The `rexec` service can be disabled with the following command:

    $ sudo chkconfig rexec off

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

References: CM-7, 68, 1436

#### Disable rsh Service [ref]rule

The `rsh` service, which is available with the `rsh-server` package and runs as a service through xinetd, should be disabled. The `rsh` service can be disabled with the following command:

    $ sudo chkconfig rsh off

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

References: CM-7, IA-5(1)(c), 68, 1436

#### Uninstal 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

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, should be disabled. The `rlogin` service can be disabled with the following command:

    $ sudo chkconfig rlogin off

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

References: CM-7, IA-5(1)(c), 1436

#### 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

References: 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 2 rules

#### Uninstall ypserv Package [ref]rule

The `ypserv` package can be uninstalled with the following command:

    $ sudo yum erase ypserv

Rationale:

Removing the `ypserv` package decreases the risk of the accidental (or intentional) activation of NIS or NIS+ services.

Severity: medium

References: CM-7, 305, 381

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 chkconfig ypbind off

Rationale:

Disabling the `ypbind` service ensures the system is not acting as a client in a NIS or NIS+ domain.

Severity: medium

References: 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

### 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 4 rules

#### Disable tftp Service [ref]rule

The `tftp` service should be disabled. The `tftp` service can be disabled with the following command:

    $ sudo chkconfig tftp off

Rationale:

Disabling the `tftp` service ensures the system is not acting as a TFTP server, which does not provide encryption or authentication.

Severity: medium

References: CM-7, 1436

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 tftp

Remediation Ansible snippet: (show)

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

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

#### 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.

Severity: medium

References: CM-7, 305

#### Remove tftp [ref]rule

Trivial File Transfer Protocol (TFTP) is a simple file transfer protocol, typically used to automatically transfer configuration or boot files between machines. TFTP does not support authentication and can be easily hacked. The package `tftp` is a client program that allows for connections to a `tftp` server.

Rationale:

It is recommended that TFTP be remvoed, unless there is a specific need for TFTP (such as a boot server). In that case, use extreme caution when configuring the services.

Severity: low

#### 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: high

References: CM-7, 366

### Base Services [ref]group

This section addresses the base services that are installed on a Red Hat Enterprise Linux 6 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 24 rules

#### Disable Automatic Bug Reporting Tool (abrtd) [ref]rule

The Automatic Bug Reporting Tool (`abrtd`) daemon collects and reports crash data when an application crash is detected. Using a variety of plugins, abrtd can email crash reports to system administrators, log crash reports to files, or forward crash reports to a centralized issue tracking system such as RHTSupport. The `abrtd` service can be disabled with the following command:

    $ sudo chkconfig abrtd off

Rationale:

Mishandling crash data could expose sensitive information about vulnerabilities in software executing on the local machine, as well as sensitive information from within a process's address space or registers.

Severity: low

References: CM-7, 381

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 abrtd

Remediation Ansible snippet: (show)

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

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

#### Disable Advanced Configuration and Power Interface (acpid) [ref]rule

The Advanced Configuration and Power Interface Daemon (`acpid`) dispatches ACPI events (such as power/reset button depressed) to userspace programs. The `acpid` service can be disabled with the following command:

    $ sudo chkconfig acpid off

Rationale:

ACPI support is highly desirable for systems in some network roles, such as laptops or desktops. For other systems, such as servers, it may permit accidental or trivially achievable denial of service situations and disabling it is appropriate.

Severity: low

References: CM-7

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 acpid

Remediation Ansible snippet: (show)

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

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

#### Disable Certmonger Service (certmonger) [ref]rule

Certmonger is a D-Bus based service that attempts to simplify interaction with certifying authorities on networks which use public-key infrastructure. It is often combined with Red Hat's IPA (Identity Policy Audit) security information management solution to aid in the management of certificates. The `certmonger` service can be disabled with the following command:

    $ sudo chkconfig certmonger off

Rationale:

The services provided by certmonger may be essential for systems fulfilling some roles a PKI infrastructure, but its functionality is not necessary for many other use cases.

Severity: low

References: CM-7

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 certmonger

Remediation Ansible snippet: (show)

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

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

#### Disable Control Group Config (cgconfig) [ref]rule

Control groups allow an administrator to allocate system resources (such as CPU, memory, network bandwidth, etc) among a defined group (or groups) of processes executing on a system. The `cgconfig` daemon starts at boot and establishes the predefined control groups. The `cgconfig` service can be disabled with the following command:

    $ sudo chkconfig cgconfig off

Rationale:

Unless control groups are used to manage system resources, running the cgconfig service is not necessary.

Severity: low

References: CM-7

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 cgconfig

Remediation Ansible snippet: (show)

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

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

#### Disable Control Group Rules Engine (cgred) [ref]rule

The `cgred` service moves tasks into control groups according to parameters set in the `/etc/cgrules.conf` configuration file. The `cgred` service can be disabled with the following command:

    $ sudo chkconfig cgred off

Rationale:

Unless control groups are used to manage system resources, running the cgred service service is not necessary.

Severity: low

References: CM-7

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 cgred

Remediation Ansible snippet: (show)

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

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

#### Disable CPU Speed (cpuspeed) [ref]rule

The `cpuspeed` service can adjust the clock speed of supported CPUs based upon the current processing load thereby conserving power and reducing heat. The `cpuspeed` service can be disabled with the following command:

    $ sudo chkconfig cpuspeed off

Rationale:

The `cpuspeed` service is only necessary if adjusting the CPU clock speed provides benefit. Traditionally this has included laptops (to enhance battery life), but may also apply to server or desktop environments where conserving power is highly desirable or necessary.

Severity: low

References: CM-7

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 cpuspeed

Remediation Ansible snippet: (show)

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

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

#### Disable Hardware Abstraction Layer Service (haldaemon) [ref]rule

The Hardware Abstraction Layer Daemon (`haldaemon`) collects and maintains information about the system's hardware configuration. This service is required on a workstation running a desktop environment, and may be necessary on any system which deals with removable media or devices. The `haldaemon` service can be disabled with the following command:

    $ sudo chkconfig haldaemon off

Rationale:

The haldaemon provides essential functionality on systems that use removable media or devices, but can be disabled for systems that do not require these.

Severity: low

References: CM-7

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 haldaemon

Remediation Ansible snippet: (show)

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

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

#### Enable IRQ Balance (irqbalance) [ref]rule

The `irqbalance` service optimizes the balance between power savings and performance through distribution of hardware interrupts across multiple processors. The `irqbalance` service can be enabled with the following command:

    $ sudo chkconfig --level 2345 irqbalance on

Rationale:

In an environment with multiple processors (now common), the irqbalance service provides potential speedups for handling interrupt requests.

Severity: low

References: CM-7

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 irqbalance

Remediation Ansible snippet: (show)

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

    - name: Enable service irqbalance
      service:
        name="{{item}}"
        enabled="yes"
        state="started"
      with_items:
        - irqbalance

#### 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 chkconfig kdump off

Rationale:

Unless the system is used for kernel development or testing, there is little need to run the kdump service.

Severity: low

References: CM-7

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

#### Disable Software RAID Monitor (mdmonitor) [ref]rule

The `mdmonitor` service is used for monitoring a software RAID array; hardware RAID setups do not use this service. The `mdmonitor` service can be disabled with the following command:

    $ sudo chkconfig mdmonitor off

Rationale:

If software RAID monitoring is not required, there is no need to run this service.

Severity: low

References: CM-7

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 mdmonitor

Remediation Ansible snippet: (show)

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

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

#### Disable D-Bus IPC Service (messagebus) [ref]rule

D-Bus provides an IPC mechanism used by a growing list of programs, such as those used for Gnome, Bluetooth, and Avahi. Due to these dependencies, disabling D-Bus may not be practical for many systems. The `messagebus` service can be disabled with the following command:

    $ sudo chkconfig messagebus off

Rationale:

If no services which require D-Bus are needed, then it can be disabled. As a broker for IPC between processes of different privilege levels, it could be a target for attack. However, disabling D-Bus is likely to be impractical for any system which needs to provide a graphical login session.

Severity: low

References: CM-7

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 messagebus

Remediation Ansible snippet: (show)

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

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

#### Disable Network Console (netconsole) [ref]rule

The `netconsole` service is responsible for loading the netconsole kernel module, which logs kernel printk messages over UDP to a syslog server. This allows debugging of problems where disk logging fails and serial consoles are impractical. The `netconsole` service can be disabled with the following command:

    $ sudo chkconfig netconsole off

Rationale:

The `netconsole` service is not necessary unless there is a need to debug kernel panics, which is not common.

Severity: low

References: CM-7, 381

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 netconsole

Remediation Ansible snippet: (show)

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

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

#### Disable ntpdate Service (ntpdate) [ref]rule

The `ntpdate` service sets the local hardware clock by polling NTP servers when the system boots. It synchronizes to the NTP servers listed in `/etc/ntp/step-tickers` or `/etc/ntp.conf` and then sets the local hardware clock to the newly synchronized system time. The `ntpdate` service can be disabled with the following command:

    $ sudo chkconfig ntpdate off

Rationale:

The `ntpdate` service may only be suitable for systems which are rebooted frequently enough that clock drift does not cause problems between reboots. In any event, the functionality of the ntpdate service is now available in the ntpd program and should be considered deprecated.

Severity: low

References: CM-7, 382

#### Disable Odd Job Daemon (oddjobd) [ref]rule

The `oddjobd` service exists to provide an interface and access control mechanism through which specified privileged tasks can run tasks for unprivileged client applications. Communication with `oddjobd` through the system message bus. The `oddjobd` service can be disabled with the following command:

    $ sudo chkconfig oddjobd off

Rationale:

The `oddjobd` service may provide necessary functionality in some environments, and can be disabled if it is not needed. Execution of tasks by privileged programs, on behalf of unprivileged ones, has traditionally been a source of privilege escalation security issues.

Severity: low

References: CM-7, 381

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 oddjobd

Remediation Ansible snippet: (show)

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

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

#### Disable Portreserve (portreserve) [ref]rule

The `portreserve` service is a TCP port reservation utility that can be used to prevent portmap from binding to well known TCP ports that are required for other services. The `portreserve` service can be disabled with the following command:

    $ sudo chkconfig portreserve off

Rationale:

The `portreserve` service provides helpful functionality by preventing conflicting usage of ports in the reserved port range, but it can be disabled if not needed.

Severity: low

References: CM-7

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 portreserve

Remediation Ansible snippet: (show)

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

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

#### Enable Process Accounting (psacct) [ref]rule

The process accounting service, `psacct`, works with programs including `acct` and `ac` to allow system administrators to view user activity, such as commands issued by users of the system. The `psacct` service can be enabled with the following command:

    $ sudo chkconfig --level 2345 psacct on

Rationale:

The `psacct` service can provide administrators a convenient view into some user activities. However, it should be noted that the auditing system and its audit records provide more authoritative and comprehensive records.

Severity: low

References: AU-12, CM-7

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 psacct

Remediation Ansible snippet: (show)

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

    - name: Enable service psacct
      service:
        name="{{item}}"
        enabled="yes"
        state="started"
      with_items:
        - psacct

#### Disable Apache Qpid (qpidd) [ref]rule

The `qpidd` service provides high speed, secure, guaranteed delivery services. It is an implementation of the Advanced Message Queuing Protocol. By default the qpidd service will bind to port 5672 and listen for connection attempts. The `qpidd` service can be disabled with the following command:

    $ sudo chkconfig qpidd off

Rationale:

The qpidd service is automatically installed when the "base" package selection is selected during installation. The qpidd service listens for network connections, which increases the attack surface of the system. If the system is not intended to receive AMQP traffic, then the `qpidd` service is not needed and should be disabled or removed.

Severity: low

References: CM-7, 382

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 qpidd

Remediation Ansible snippet: (show)

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

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

#### Disable Quota Netlink (quota_nld) [ref]rule

The `quota_nld` service provides notifications to users of disk space quota violations. It listens to the kernel via a netlink socket for disk quota violations and notifies the appropriate user of the violation using D-Bus or by sending a message to the terminal that the user has last accessed. The `quota_nld` service can be disabled with the following command:

    $ sudo chkconfig quota_nld off

Rationale:

If disk quotas are enforced on the local system, then the `quota_nld` service likely provides useful functionality and should remain enabled. However, if disk quotas are not used or user notification of disk quota violation is not desired then there is no need to run this service.

Severity: low

References: CM-7

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 quota_nld

Remediation Ansible snippet: (show)

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

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

#### Disable Network Router Discovery Daemon (rdisc) [ref]rule

The `rdisc` service implements the client side of the ICMP Internet Router Discovery Protocol (IRDP), which allows discovery of routers on the local subnet. If a router is discovered then the local routing table is updated with a corresponding default route. By default this daemon is disabled. The `rdisc` service can be disabled with the following command:

    $ sudo chkconfig rdisc off

Rationale:

General-purpose systems typically have their network and routing information configured statically by a system administrator. Workstations or some special-purpose systems often use DHCP (instead of IRDP) to retrieve dynamic network configuration information.

Severity: low

References: AC-4, CM-7, 382

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 rdisc

Remediation Ansible snippet: (show)

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

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

#### Disable Red Hat Network Service (rhnsd) [ref]rule

The Red Hat Network service automatically queries Red Hat Network servers to determine whether there are any actions that should be executed, such as package updates. This only occurs if the system was registered to an RHN server or satellite and managed as such. The `rhnsd` service can be disabled with the following command:

    $ sudo chkconfig rhnsd off

Rationale:

Although systems management and patching is extremely important to system security, management by a system outside the enterprise enclave is not desirable for some environments. However, if the system is being managed by RHN or RHN Satellite Server the `rhnsd` daemon can remain on.

Severity: low

References: CM-7, 382

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 rhnsd

Remediation Ansible snippet: (show)

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

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

#### Disable Red Hat Subscription Manager Daemon (rhsmcertd) [ref]rule

The Red Hat Subscription Manager (rhsmcertd) periodically checks for changes in the entitlement certificates for a registered system and updates it accordingly. The `rhsmcertd` service can be disabled with the following command:

    $ sudo chkconfig rhsmcertd off

Rationale:

The `rhsmcertd` service can provide administrators with some additional control over which of their systems are entitled to particular subscriptions. However, for systems that are managed locally or which are not expected to require remote changes to their subscription status, it is unnecessary and can be disabled.

Severity: low

References: CM-7

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 rhsmcertd

Remediation Ansible snippet: (show)

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

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

#### Disable Cyrus SASL Authentication Daemon (saslauthd) [ref]rule

The `saslauthd` service handles plaintext authentication requests on behalf of the SASL library. The service isolates all code requiring superuser privileges for SASL authentication into a single process, and can also be used to provide proxy authentication services to clients that do not understand SASL based authentication. The `saslauthd` service can be disabled with the following command:

    $ sudo chkconfig saslauthd off

Rationale:

The `saslauthd` service provides essential functionality for performing authentication in some directory environments, such as those which use Kerberos and LDAP. For others, however, in which only local files may be consulted, it is not necessary and should be disabled.

Severity: low

References: CM-7

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 saslauthd

Remediation Ansible snippet: (show)

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

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

#### Disable SMART Disk Monitoring Service (smartd) [ref]rule

SMART (Self-Monitoring, Analysis, and Reporting Technology) is a feature of hard drives that allows them to detect symptoms of disk failure and relay an appropriate warning. The `smartd` service can be disabled with the following command:

    $ sudo chkconfig smartd off

Rationale:

SMART can help protect against denial of service due to failing hardware. Nevertheless, if it is not needed or the system's drives are not SMART-capable (such as solid state drives), it can be disabled.

Severity: low

References: CM-7

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 smartd

Remediation Ansible snippet: (show)

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

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

#### Disable System Statistics Reset Service (sysstat) [ref]rule

The `sysstat` service resets various I/O and CPU performance statistics to zero in order to begin counting from a fresh state at boot time. The `sysstat` service can be disabled with the following command:

    $ sudo chkconfig sysstat off

Rationale:

By default the `sysstat` service merely runs a program at boot to reset the statistics, which can be retrieved using programs such as `sar` and `sadc`. These may provide useful insight into system operation, but unless used this service can be disabled.

Severity: low

References: CM-7

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 sysstat

Remediation Ansible snippet: (show)

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

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

### 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 2 rules

#### 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 chkconfig --level 2345 crond on

Rationale:

Due to its usage for maintenance and security-supporting tasks, enabling the cron daemon is essential.

Severity: medium

References: CM-7

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

#### Disable At Service (atd) [ref]rule

The `at` and `batch` commands can be used to schedule tasks that are meant to be executed only once. This allows delayed execution in a manner similar to cron, except that it is not recurring. The daemon `atd` keeps track of tasks scheduled via `at` and `batch`, and executes them at the specified time. The `atd` service can be disabled with the following command:

    $ sudo chkconfig atd off

Rationale:

The `atd` service could be used by an unsophisticated insider to carry out activities outside of a normal login session, which could complicate accountability. Furthermore, the need to schedule tasks with `at` or `batch` is not common.

Severity: low

References: CM-7, 381

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 atd

Remediation Ansible snippet: (show)

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

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

### 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 10 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 10 rules

#### 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 suffers from design flaws that result in security vulnerabilities and should not be used.

Severity: high

References: AC-3(10), IA-5(1)(c), 776, 774, 1436

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-27072-8' '%s %s'

#### 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 300

The timeout interval is given in seconds. To have a timeout of 15 minutes, set interval to 900.
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:

Causing idle users to be automatically logged out guards against compromises one system leading trivially to compromises on another.

Severity: low

References: AC-2(5), SA-8, 879, 1133

Remediation Shell script: (show)

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

    sshd_idle_timeout_value="300"

    grep -q ^ClientAliveInterval /etc/ssh/sshd_config && \
      sed -i "s/ClientAliveInterval.*/ClientAliveInterval $sshd_idle_timeout_value/g" /etc/ssh/sshd_config
    if ! [ $? -eq 0 ]; then
        echo "ClientAliveInterval $sshd_idle_timeout_value" >> /etc/ssh/sshd_config
    fi

#### 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: low

References: AC-2(5), SA-8, 879, 1133

Remediation Shell script: (show)

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

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

#### 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

References: AC-3, 765, 766

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-27124-7' '%s %s'

#### 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

References: AC-3, 765, 766

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

#### 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:

Permitting direct root login reduces auditable information about who ran privileged commands on the system and also allows direct attack attempts on root's password.

Severity: medium

References: AC-3, AC-6(2), IA-2(1), 770

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 remote 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

References: AC-3, 765, 766

Remediation Shell script: (show)

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

    grep -q ^PermitEmptyPasswords /etc/ssh/sshd_config && \
      sed -i "s/PermitEmptyPasswords.*/PermitEmptyPasswords no/g" /etc/ssh/sshd_config
    if ! [ $? -eq 0 ]; then
        echo "PermitEmptyPasswords no" >> /etc/ssh/sshd_config
    fi

#### 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 login 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

References: AC-8(a), 48

Remediation Shell script: (show)

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

    grep -q ^Banner /etc/ssh/sshd_config && \
      sed -i "s/Banner.*/Banner \/etc\/issue/g" /etc/ssh/sshd_config
    if ! [ $? -eq 0 ]; then
        echo "Banner /etc/issue" >> /etc/ssh/sshd_config
    fi

#### Do Not Allow SSH Environment Options [ref]rule

To ensure users are not able to present 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: low

References: 1414

Remediation Shell script: (show)

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

    grep -q ^PermitUserEnvironment /etc/ssh/sshd_config && \
      sed -i "s/PermitUserEnvironment.*/PermitUserEnvironment no/g" /etc/ssh/sshd_config
    if ! [ $? -eq 0 ]; then
        echo "PermitUserEnvironment no" >> /etc/ssh/sshd_config
    fi

#### 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,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc

The man page `sshd_config(5)` contains a list of supported ciphers. Rationale:

Approved algorithms should impart some level of confidence in their implementation. These are also required for compliance.

Severity: medium

References: AC-3, AC-17(2), SI-7, IA-5(1)(c), IA-7, 803, 1144, 1145, 1146

Remediation Shell script: (show)

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

    grep -q ^Ciphers /etc/ssh/sshd_config && \
      sed -i "s/Ciphers.*/Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc/g" /etc/ssh/sshd_config
    if ! [ $? -eq 0 ]; then
        echo "Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc" >> /etc/ssh/sshd_config
    fi

### Avahi Server [ref]group

The Avahi daemon implements the DNS Service Discovery and Multicast DNS protocols, which provide service and host discovery on a network. It allows a system to automatically identify resources on the network, such as printers or web servers. This capability is also known as mDNSresponder and is a major part of Zeroconf networking.

contains 1 rule

### Disable Avahi Server if Possible [ref]group

Because the Avahi daemon service keeps an open network port, it is subject to network attacks. Disabling it can reduce the system's vulnerability to such attacks.

contains 1 rule

#### Disable Avahi Server Software [ref]rule

The `avahi-daemon` service can be disabled with the following command:

    $ sudo chkconfig avahi-daemon off

Rationale:

Because the Avahi daemon service keeps an open network port, it is subject to network attacks. Its functionality is convenient but is only appropriate if the local network can be trusted.

Severity: low

References: CM-7, 366

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 avahi-daemon

Remediation Ansible snippet: (show)

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

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

### Print Support [ref]group

The Common Unix Printing System (CUPS) service provides both local and network printing support. A system running the CUPS service can accept print jobs from other systems, process them, and send them to the appropriate printer. It also provides an interface for remote administration through a web browser. The CUPS service is installed and activated by default. The project homepage and more detailed documentation are available at http://www.cups.org.

contains 3 rules

### Configure the CUPS Service if Necessary [ref]group

CUPS provides the ability to easily share local printers with other machines over the network. It does this by allowing machines to share lists of available printers. Additionally, each machine that runs the CUPS service can potentially act as a print server. Whenever possible, the printer sharing and print server capabilities of CUPS should be limited or disabled. The following recommendations should demonstrate how to do just that.

contains 2 rules

#### Disable Printer Browsing Entirely if Possible [ref]rule

By default, CUPS listens on the network for printer list broadcasts on UDP port 631. This functionality is called printer browsing. To disable printer browsing entirely, edit the CUPS configuration file, located at `/etc/cups/cupsd.conf`, to include the following:

    Browsing Off

Rationale:

The CUPS print service can be configured to broadcast a list of available printers to the network. Other machines on the network, also running the CUPS print service, can be configured to listen to these broadcasts and add and configure these printers for immediate use. By disabling this browsing capability, the machine will no longer generate or receive such broadcasts.

Severity: low

References: CM-7

#### Disable Print Server Capabilities [ref]rule

To prevent remote users from potentially connecting to and using locally configured printers, disable the CUPS print server sharing capabilities. To do so, limit how the server will listen for print jobs by removing the more generic port directive from /etc/cups/cupsd.conf:

    Port 631

and replacing it with the `Listen` directive:

    Listen localhost:631

This will prevent remote users from printing to locally configured printers while still allowing local users on the machine to print normally. Rationale:

By default, locally configured printers will not be shared over the network, but if this functionality has somehow been enabled, these recommendations will disable it again. Be sure to disable outgoing printer list broadcasts, or remote users will still be able to see the locally configured printers, even if they cannot actually print to them. To limit print serving to a particular set of users, use the Policy directive.

Severity: low

References: CM-7

#### Disable the CUPS Service [ref]rule

The `cups` service can be disabled with the following command:

    $ sudo chkconfig cups off

Rationale:

Turn off unneeded services to reduce attack surface.

Severity: low

References: CM-7

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 cups

Remediation Ansible snippet: (show)

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

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

### DHCP [ref]group

The Dynamic Host Configuration Protocol (DHCP) allows systems to request and obtain an IP address and other configuration parameters from a server.
This guide recommends configuring networking on clients by manually editing the appropriate files under `/etc/sysconfig`. Use of DHCP can make client systems vulnerable to compromise by rogue DHCP servers, and should be avoided unless necessary. If using DHCP is necessary, however, there are best practices that should be followed to minimize security risk.

contains 3 rules

### Disable DHCP Server [ref]group

The DHCP server `dhcpd` is not installed or activated by default. If the software was installed and activated, but the system does not need to act as a DHCP server, it should be disabled and removed.

contains 2 rules

#### Disable DHCP Service [ref]rule

The `dhcpd` service should be disabled on any system that does not need to act as a DHCP server. The `dhcpd` service can be disabled with the following command:

    $ sudo chkconfig dhcpd off

Rationale:

Unmanaged or unintentionally activated DHCP servers may provide faulty information to clients, interfering with the operation of a legitimate site DHCP server if there is one.

Severity: medium

References: CM-7, 366

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 dhcpd

Remediation Ansible snippet: (show)

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

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

#### Uninstall DHCP Server Package [ref]rule

If the system does not need to act as a DHCP server, the dhcp package can be uninstalled. The `dhcp` package can be removed with the following command:

    $ sudo yum erase dhcp

Rationale:

Removing the DHCP server ensures that it cannot be easily or accidentally reactivated and disrupt network operation.

Severity: medium

References: CM-7, 366

### Disable DHCP Client [ref]group

DHCP is the default network configuration method provided by the system installer, and common on many networks. Nevertheless, manual management of IP addresses for systems implies a greater degree of management and accountability for network activity.

contains 1 rule

#### Disable DHCP Client [ref]rule

For each interface on the system (e.g. eth0), edit `/etc/sysconfig/network-scripts/ifcfg-interface` and make the following changes:

- Correct the BOOTPROTO line to read:

      BOOTPROTO=none

- Add or correct the following lines, substituting the appropriate values based on your site's addressing scheme:

      NETMASK=255.255.255.0
      IPADDR=192.168.1.2
      GATEWAY=192.168.1.1

Rationale:

DHCP relies on trusting the local network. If the local network is not trusted, then it should not be used. However, the automatic configuration provided by DHCP is commonly used and the alternative, manual configuration, presents an unacceptable burden in many circumstances.

Severity: low

References: CM-7, 366

### 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.
More information on how to configure the NTP server software, including configuration of cryptographic authentication for time data, is available at http://www.ntp.org.

contains 3 rules

#### Enable the NTP Daemon [ref]rule

The `ntpd` service can be enabled with the following command:

    $ sudo chkconfig --level 2345 ntpd on

Rationale:

Enabling the `ntpd` service ensures that the `ntpd` service 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 NTP daemon offers 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

References: AU-8(1), 160

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 ntpd

Remediation Ansible snippet: (show)

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

    - name: Enable service ntpd
      service:
        name="{{item}}"
        enabled="yes"
        state="started"
      with_items:
        - ntpd

#### Specify a Remote NTP Server [ref]rule

To specify a remote NTP server for time synchronization, edit the file `/etc/ntp.conf`. 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

References: AU-8(1), 160

#### Specify Additional Remote NTP Servers [ref]rule

Additional NTP servers can be specified for time synchronization in the file `/etc/ntp.conf`. To do so, 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

References: AU-8(1)

### Mail Server Software [ref]group

Mail servers are used to send and receive email over the network. Mail is a very common service, and Mail Transfer Agents (MTAs) are obvious targets of network attack. Ensure that machines are not running MTAs unnecessarily, and configure needed MTAs as defensively as possible.
Very few systems at any site should be configured to directly receive email over the network. Users should instead use mail client programs to retrieve email from a central server that supports protocols such as IMAP or POP3. However, it is normal for most systems to be independently capable of sending email, for instance so that cron jobs can report output to an administrator. Most MTAs, including Postfix, support a submission-only mode in which mail can be sent from the local system to a central site MTA (or directly delivered to a local account), but the system still cannot receive mail directly over a network.
The `alternatives` program in Red Hat Enterprise Linux permits selection of other mail server software (such as Sendmail), but Postfix is the default and is preferred. Postfix was coded with security in mind and can also be more effectively contained by SELinux as its modular design has resulted in separate processes performing specific actions. More information is available on its website, http://www.postfix.org.

contains 2 rules

### Configure SMTP For Mail Clients [ref]group

This section discusses settings for Postfix in a submission-only e-mail configuration.

contains 1 rule

#### Disable Postfix Network Listening [ref]rule

Edit the file `/etc/postfix/main.cf` to ensure that only the following `inet_interfaces` line appears:

    inet_interfaces = localhost

Rationale:

This ensures `postfix` accepts mail messages (such as cron job reports) from the local system only, and not from the network, which protects it from network attack.

Severity: medium

References: CM-7, 382

#### Uninstall Sendmail Package [ref]rule

Sendmail is not the default mail transfer agent and is not installed by default. The `sendmail` package can be removed with the following command:

    $ sudo yum erase sendmail

Rationale:

The sendmail software was not developed with security in mind and its design prevents it from being effectively contained by SELinux. Postfix should be used instead.

Severity: medium

References: CM-7

### 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 6 includes software that enables a system to act as both an LDAP client and server.

contains 3 rules

### 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 6 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 6 is available at https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_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 2 rules

#### Configure LDAP Client to Use TLS For All Transactions [ref]rule

Configure LDAP to enforce TLS use. First, edit the file `/etc/pam_ldap.conf`, and add or correct the following lines:

    ssl start_tls

Then review the LDAP server and ensure TLS has been configured. Rationale:

The ssl directive specifies whether to use ssl 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

References: CM-7, 776, 778, 1453

#### Configure Certificate Directives for LDAP Use of TLS [ref]rule

Ensure a copy of a trusted CA certificate has been placed in the file `/etc/pki/tls/CA/cacert.pem`. Configure LDAP to enforce TLS use and to trust certificates signed by that CA. First, edit the file `/etc/pam_ldap.conf`, and add or correct either of the following lines:

    tls_cacertdir /etc/pki/tls/CA

or

    tls_cacertfile /etc/pki/tls/CA/cacert.pem

Then review the LDAP server and ensure TLS has been configured. Rationale:

The tls_cacertdir or tls_cacertfile directives are required when tls_checkpeer is configured (which is the default for openldap versions 2.1 and up). These directives define the path to the trust certificates signed by the site CA.

Severity: medium

References: CM-7, 776, 778, 1453

### Configure OpenLDAP Server [ref]group

This section details some security-relevant settings for an OpenLDAP server. Installation and configuration of OpenLDAP on Red Hat Enterprise Linux 6 is available at: https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/ch-Directory_Servers.html.

contains 1 rule

#### Uninstall openldap-servers Package [ref]rule

The `openldap-servers` package should be removed if not in use. Is this machine the OpenLDAP server? If not, remove the package.

    $ sudo yum erase openldap-servers

The openldap-servers RPM is not installed by default on Red Hat Enterprise Linux 6 machines. It is needed only by the OpenLDAP server, not by the clients which use LDAP for authentication. If the system is not intended for use as an LDAP Server it should be removed. Rationale:

The `openldap-servers` package is not installed by default on RHEL6 machines. It is needed only by the OpenLDAP server system, not clients which use LDAP for authentication. If the system is not intended for use as an LDAP server, `openldap-servers` should be removed.

Severity: low

References: CM-7, 366

### 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 2 rules

### Configure NFS Clients [ref]group

The steps in this section are appropriate for machines which operate as NFS clients.

contains 2 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 2 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

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

### DNS Server [ref]group

Most organizations have an operational need to run at least one nameserver. However, there are many common attacks involving DNS server software, and this server software should be disabled on any system on which it is not needed.

contains 2 rules

### Disable DNS Server [ref]group

DNS software should be disabled on any machine which does not need to be a nameserver. Note that the BIND DNS server software is not installed on Red Hat Enterprise Linux 6 by default. The remainder of this section discusses secure configuration of machines which must be nameservers.

contains 2 rules

#### Disable DNS Server [ref]rule

The `named` service can be disabled with the following command:

    $ sudo chkconfig named off

Rationale:

All network services involve some risk of compromise due to implementation flaws and should be disabled if possible.

Severity: low

References: CM-7, 366

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 named

Remediation Ansible snippet: (show)

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

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

#### Uninstall bind Package [ref]rule

To remove the `bind` package, which contains the `named` service, run the following command:

    $ sudo yum erase bind

Rationale:

If there is no need to make DNS server software available, removing it provides a safeguard against its activation.

Severity: low

References: CM-7, 366

### 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 1 rule

### 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: low

References: CM-7, 1436

### Web Server [ref]group

The web server is responsible for providing access to content via the HTTP protocol. Web servers represent a significant security risk because:

- The HTTP port is commonly probed by malicious sources
- Web server software is very complex, and includes a long history of vulnerabilities
- The HTTP protocol is unencrypted and vulnerable to passive monitoring

The system's default web server software is Apache 2 and is provided in the RPM package `httpd`.

contains 2 rules

### Disable Apache if Possible [ref]group

If Apache was installed and activated, but the system does not need to act as a web server, then it should be disabled and removed from the system.

contains 2 rules

#### Disable httpd Service [ref]rule

The `httpd` service can be disabled with the following command:

    $ sudo chkconfig httpd off

Rationale:

Running web server software provides a network-based avenue of attack, and should be disabled if not needed.

Severity: low

References: CM-7

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 httpd

Remediation Ansible snippet: (show)

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

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

#### Uninstall httpd Package [ref]rule

The `httpd` package can be removed with the following command:

    $ sudo yum erase httpd

Rationale:

If there is no need to make the web server software available, removing it provides a safeguard against its activation.

Severity: low

References: CM-7

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 httpd

Remediation Ansible snippet: (show)

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

    - name: Ensure httpd is removed
      package:
        name="{{item}}"
        state=absent
      with_items:
        - httpd

Remediation Puppet snippet: (show)

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

    include remove_httpd

    class remove_httpd {
      package { 'httpd':
        ensure => 'purged',
      }
    }

Remediation Anaconda snippet: (show)

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

    package -remove=httpd

### Samba(SMB) Microsoft Windows File Sharing Server [ref]group

When properly configured, the Samba service allows Linux machines to provide file and print sharing to Microsoft Windows machines. There are two software packages that provide Samba support. The first, `samba-client`, provides a series of command line tools that enable a client machine to access Samba shares. The second, simply labeled `samba`, provides the Samba service. It is this second package that allows a Linux machine to act as an Active Directory server, a domain controller, or as a domain member. Only the `samba-client` package is installed by default.

contains 2 rules

### Configure Samba if Necessary [ref]group

All settings for the Samba daemon can be found in `/etc/samba/smb.conf`. Settings are divided between a `[global]` configuration section and a series of user created share definition sections meant to describe file or print shares on the system. By default, Samba will operate in user mode and allow client machines to access local home directories and printers. It is recommended that these settings be changed or that additional limitations be set in place.

contains 2 rules

#### Require Client SMB Packet Signing, if using smbclient [ref]rule

To require samba clients running `smbclient` to use packet signing, add the following to the `[global]` section of the Samba configuration file, `/etc/samba/smb.conf`:

    client signing = mandatory

Requiring samba clients such as `smbclient` to use packet signing ensures they can only communicate with servers that support packet signing. Rationale:

Packet signing can prevent man-in-the-middle attacks which modify SMB packets in transit.

Severity: low

Remediation Shell script: (show)

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

    ######################################################################
    #By Luke "Brisk-OH" Brisk
    #luke.brisk@boeing.com or luke.brisk@gmail.com
    ######################################################################

    CLIENTSIGNING=$( grep -ic 'client signing' /etc/samba/smb.conf )

    if [ "$CLIENTSIGNING" -eq 0 ];  then
    	# Add to global section
    	sed -i 's/\[global\]/\[global\]\n\n\tclient signing = mandatory/g' /etc/samba/smb.conf
    else
    	sed -i 's/[[:blank:]]*client[[:blank:]]signing[[:blank:]]*=[[:blank:]]*no/        client signing = mandatory/g' /etc/samba/smb.conf
    fi

#### Require Client SMB Packet Signing, if using mount.cifs [ref]rule

Require packet signing of clients who mount Samba shares using the `mount.cifs` program (e.g., those who specify shares in `/etc/fstab`). To do so, ensure signing options (either `sec=krb5i` or `sec=ntlmv2i`) are used.
See the `mount.cifs(8)` man page for more information. A Samba client should only communicate with servers who can support SMB packet signing.

Rationale:

Packet signing can prevent man-in-the-middle attacks which modify SMB packets in transit.

Severity: low

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