ikiwiki/ security

If you are using ikiwiki to render pages that only you can edit, do not generate any wrappers, and do not use the cgi, then there are no more security issues with this program than with cat(1). If, however, you let others edit pages in your wiki, then some possible security issues do need to be kept in mind.

If you find a new security vulnerability, please email the maintainers privately instead of listing it in a public bug tracker, so that we can arrange for coordinated disclosure when a fix is available. The maintainers are Joey Hess (joey@kitenet.net), Amitai Schleier (schmonz-web-ikiwiki@schmonz.com) and Jonathan Dowland (jmtd@debian.org).

# Probable holes

(The list of things to fix.)

## commit spoofing

Anyone with direct commit access can forge "web commit from foo" and make it appear on RecentChanges like foo committed. One way to avoid this would be to limit web commits to those done by a certain user.

## other stuff to look at

I have been meaning to see if any CRLF injection type things can be done in the CGI code.

# Potential gotchas

(Things not to do.)

## image file etc attacks

If it enounters a file type it does not understand, ikiwiki just copies it into place. So if you let users add any kind of file they like, they can upload images, movies, windows executables, css files, etc (though not html files). If these files exploit security holes in the browser of someone who's viewing the wiki, that can be a security problem.

Of course nobody else seems to worry about this in other wikis, so should we?

People with direct commit access can upload such files (and if you wanted to you could block that with a pre-commit hook).

The attachments plugin is not enabled by default. If you choose to enable it, you should make use of its powerful abilities to filter allowed types of attachments, and only let trusted users upload.

It is possible to embed an image in a page edited over the web, by using `img src="data:image/png;"`. Ikiwiki's htmlscrubber only allows `data:` urls to be used for `image/*` mime types. It's possible that some broken browser might ignore the mime type and if the data provided is not an image, instead run it as javascript, or something evil like that. Hopefully not many browsers are that broken.

## multiple accessors of wiki directory

If multiple people can directly write to the source directory ikiwiki is using, or to the destination directory it writes files to, then one can cause trouble for the other when they run ikiwiki through symlink attacks.

So it's best if only one person can ever directly write to those directories.

## setup files

Setup files are not safe to keep in the same revision control repository with the rest of the wiki. Just don't do it.

## page locking can be bypassed via direct commits

A locked page can only be edited on the web by an admin, but anyone who is allowed to commit directly to the repository can bypass this. This is by design, although a pre-commit hook could be used to prevent editing of locked pages, if you really need to.

## web server attacks

If your web server does any parsing of special sorts of files (for example, server parsed html files), then if you let anyone else add files to the wiki, they can try to use this to exploit your web server.

# Hopefully non-holes

(AKA, the assumptions that will be the root of most security holes...)

## exploiting ikiwiki with bad content

Someone could add bad content to the wiki and hope to exploit ikiwiki. Note that ikiwiki runs with perl taint checks on, so this is unlikely.

One fun thing in ikiwiki is its handling of a PageSpec, which involves translating it into perl and running the perl. Of course, this is done very carefully to guard against injecting arbitrary perl code.

## publishing cgi scripts

ikiwiki does not allow cgi scripts to be published as part of the wiki. Or rather, the script is published, but it's not marked executable (except in the case of "destination directory file replacement" below), so hopefully your web server will not run it.

## suid wrappers

`ikiwiki --wrapper` is intended to generate a wrapper program that runs ikiwiki to update a given wiki. The wrapper can in turn be made suid, for example to be used in a post-commit hook by people who cannot write to the html pages, etc.

If the wrapper program is made suid, then any bugs in this wrapper would be security holes. The wrapper is written as securely as I know how, is based on code that has a history of security use long before ikiwiki, and there's been no problem yet.

## shell exploits

ikiwiki does not expose untrusted data to the shell. In fact it doesn't use `system(3)` at all, and the only use of backticks is on data supplied by the wiki admin and untainted filenames.

Ikiwiki was developed and used for a long time with perl's taint checking turned on as a second layer of defense against shell and other exploits. Due to a strange bug in perl, taint checking is currently disabled for production builds of ikiwiki.

## cgi data security

When ikiwiki runs as a cgi to edit a page, it is passed the name of the page to edit. It has to make sure to sanitise this page, to prevent eg, editing of ../../../foo, or editing of files that are not part of the wiki, such as subversion dotfiles. This is done by sanitising the filename removing unallowed characters, then making sure it doesn't start with "/" or contain ".." or "/.svn/", etc. Annoyingly ad-hoc, this kind of code is where security holes breed. It needs a test suite at the very least.

## CGI::Session security

I've audited this module and it is massively insecure by default. ikiwiki uses it in one of the few secure ways; by forcing it to write to a directory it controls (and not /tmp) and by setting a umask that makes the file not be world readable.

## cgi password security

Login to the wiki using passwordauth involves sending a password in cleartext over the net. Cracking the password only allows editing the wiki as that user though. If you care, you can use https, I suppose. If you do use https either for all of the wiki, or just the cgi access, then consider using the sslcookie option. Using openid is a potentially better option.

## XSS holes in CGI output

ikiwiki has been audited to ensure that all cgi script input/output is sanitised to prevent XSS attacks. For example, a user can't register with a username containing html code (anymore).

It's difficult to know for sure if all such avenues have really been closed though.

## HTML::Template security

If the template plugin is enabled, all users can modify templates like any other part of the wiki. Some trusted users can modify templates without it too. This assumes that HTML::Template is secure when used with untrusted/malicious templates. (Note that includes are not allowed.)

# Plugins

The security of plugins depends on how well they're written and what external tools they use. The plugins included in ikiwiki are all held to the same standards as the rest of ikiwiki, but with that said, here are some security notes for them.

- The img plugin assumes that imagemagick/perlmagick are secure from malformed image attacks for at least the formats listed in `img_allowed_formats`. Imagemagick has had security holes in the past. To be able to exploit such a hole, a user would need to be able to upload images to the wiki.

# Fixed holes

(Unless otherwise noted, these were discovered and immediately fixed by the ikiwiki developers.)

## destination directory file replacement

Any file in the destination directory that is a valid page filename can be replaced, even if it was not originally rendered from a page. For example, ikiwiki.cgi could be edited in the wiki, and it would write out a replacement. File permission is preseved. Yipes!

This was fixed by making ikiwiki check if the file it's writing to exists; if it does then it has to be a file that it's aware of creating before, or it will refuse to create it.

Still, this sort of attack is something to keep in mind.

## symlink attacks

Could a committer trick ikiwiki into following a symlink and operating on some other tree that it shouldn't? svn supports symlinks, so one can get into the repo. ikiwiki uses File::Find to traverse the repo, and does not tell it to follow symlinks, but it might be possible to race replacing a directory with a symlink and trick it into following the link.

Also, if someone checks in a symlink to /etc/passwd, ikiwiki would read and publish that, which could be used to expose files a committer otherwise wouldn't see.

To avoid this, ikiwiki will skip over symlinks when scanning for pages, and uses locking to prevent more than one instance running at a time. The lock prevents one ikiwiki from running a svn up/git pull/etc at the wrong time to race another ikiwiki. So only attackers who can write to the working copy on their own can race it.

## symlink + cgi attacks

Similarly, a commit of a symlink could be made, ikiwiki ignores it because of the above, but the symlink is still there, and then you edit the page from the web, which follows the symlink when reading the page (exposing the content), and again when saving the changed page (changing the content).

This was fixed for page saving by making ikiwiki refuse to write to files that are symlinks, or that are in subdirectories that are symlinks, combined with the above locking.

For page editing, it's fixed by ikiwiki checking to make sure that it already has found a page by scanning the tree, before loading it for editing, which as described above, also is done in a way that avoids symlink attacks.

## underlaydir override attacks

ikiwiki also scans an underlaydir for pages, this is used to provide stock pages to all wikis w/o needing to copy them into the wiki. Since ikiwiki internally stores only the base filename from the underlaydir or srcdir, and searches for a file in either directory when reading a page source, there is the potential for ikiwiki's scanner to reject a file from the srcdir for some reason (such as it being contained in a directory that is symlinked in), find a valid copy of the file in the underlaydir, and then when loading the file, mistakenly load the bad file from the srcdir.

This attack is avoided by making ikiwiki refuse to add any files from the underlaydir if a file also exists in the srcdir with the same name.

## multiple page source issues

Note that I previously worried that underlay override attacks could also be accomplished if ikiwiki were extended to support other page markup languages besides markdown. However, a closer look indicates that this is not a problem: ikiwiki does preserve the file extension when storing the source filename of a page, so a file with another extension that renders to the same page name can't bypass the check. Ie, ikiwiki won't skip foo.rst in the srcdir, find foo.mdwn in the underlay, decide to render page foo and then read the bad foo.mdwn. Instead it will remember the .rst extension and only render a file with that extension.

## XSS attacks in page content

ikiwiki supports protecting users from their own broken browsers via the htmlscrubber plugin, which is enabled by default.

## svn commit logs

It's was possible to force a whole series of svn commits to appear to have come just before yours, by forging svn log output. This was guarded against by using svn log --xml.

ikiwiki escapes any html in svn commit logs to prevent other mischief.

## XML::Parser

XML::Parser is used by the aggregation plugin, and has some security holes. Bug #378411 does not seem to affect our use, since the data is not encoded as utf-8 at that point. #378412 could affect us, although it doesn't seem very exploitable. It has a simple fix, and has been fixed in Debian unstable.

## include loops

Various directives that cause one page to be included into another could be exploited to DOS the wiki, by causing a loop. Ikiwiki has always guarded against this one way or another; the current solution should detect all types of loops involving preprocessor directives.

## Online editing of existing css and images

A bug in ikiwiki allowed the web-based editor to edit any file that was in the wiki, not just files that are page sources. So an attacker (or a genuinely helpful user, which is how the hole came to light) could edit files like style.css. It is also theoretically possible that an attacker could have used this hole to edit images or other files in the wiki, with some difficulty, since all editing would happen in a textarea.

This hole was discovered on 10 Feb 2007 and fixed the same day with the release of ikiwiki 1.42. A fix was also backported to Debian etch, as version 1.33.1. I recommend upgrading to one of these versions if your wiki allows web editing.

## html insertion via title

Missing html escaping of the title contents allowed a web-based editor to insert arbitrary html inside the title tag of a page. Since that part of the page is not processed by the htmlscrubber, evil html could be injected.

This hole was discovered on 21 March 2007 and fixed the same day (er, hour) with the release of ikiwiki 1.46. A fix was also backported to Debian etch, as version 1.33.2. I recommend upgrading to one of these versions if your wiki allows web editing or aggregates feeds.

## javascript insertion via meta tags

It was possible to use the meta plugin's meta tags to insert arbitrary url contents, which could be used to insert stylesheet information containing javascript. This was fixed by sanitising meta tags.

This hole was discovered on 21 March 2007 and fixed the same day with the release of ikiwiki 1.47. A fix was also backported to Debian etch, as version 1.33.3. I recommend upgrading to one of these versions if your wiki can be edited by third parties.

## insufficient checking for symlinks in srcdir path

Ikiwiki did not check if path to the srcdir to contained a symlink. If an attacker had commit access to the directories in the path, they could change it to a symlink, causing ikiwiki to read and publish files that were not intended to be published. (But not write to them due to other checks.)

In most configurations, this is not exploitable, because the srcdir is checked out of revision control, but the directories leading up to it are not. Or, the srcdir is a single subdirectory of a project in revision control (ie, `ikiwiki/doc`), and if the subdirectory were a symlink, ikiwiki would still typically not follow it.

There are at least two configurations where this is exploitable:

- If the srcdir is a deeper subdirectory of a project. For example if it is `project/foo/doc`, an an attacker can replace `foo` with a symlink to a directory containing a `doc` directory (not a symlink), then ikiwiki would follow the symlink.
- If the path to the srcdir in ikiwiki's configuration ended in "/", and the srcdir is a single subdirectory of a project, (ie, `ikiwiki/doc/`), the srcdir could be a symlink and ikiwiki would not notice.

This security hole was discovered on 26 November 2007 and fixed the same day with the release of ikiwiki 2.14. I recommend upgrading to this version if your wiki can be committed to by third parties. Alternatively, don't use a trailing slash in the srcdir, and avoid the (unusual) configurations that allow the security hole to be exploited.

## javascript insertion via uris

The htmlscrubber did not block javascript in uris. This was fixed by adding a whitelist of valid uri types, which does not include javascript. (CVE-2008-0809) Some urls specifyable by the meta plugin could also theoretically have been used to inject javascript; this was also blocked (CVE-2008-0808).

This hole was discovered on 10 February 2008 and fixed the same day with the release of ikiwiki 2.31.1. (And a few subsequent versions..) A fix was also backported to Debian etch, as version 1.33.4. I recommend upgrading to one of these versions if your wiki can be edited by third parties.

## Cross Site Request Forging

Cross Site Request Forging could be used to constuct a link that would change a logged-in user's password or other preferences if they clicked on the link. It could also be used to construct a link that would cause a wiki page to be modified by a logged-in user. (CVE-2008-0165)

These holes were discovered on 10 April 2008 and fixed the same day with the release of ikiwiki 2.42. A fix was also backported to Debian etch, as version 1.33.5. I recommend upgrading to one of these versions.

## Cleartext passwords

Until version 2.48, ikiwiki stored passwords in cleartext in the `userdb`. That risks exposing all users' passwords if the file is somehow exposed. To pre-emtively guard against that, current versions of ikiwiki store password hashes (using Eksblowfish).

If you use the passwordauth plugin, I recommend upgrading to ikiwiki 2.48, installing the Authen::Passphrase perl module, and running `ikiwiki-transition hashpassword` to replace all existing cleartext passwords with strong blowfish hashes.

You might also consider changing to openid, which does not require ikiwiki deal with passwords at all, and does not involve users sending passwords in cleartext over the net to log in, either.

## Empty password security hole

This hole allowed ikiwiki to accept logins using empty passwords, to openid accounts that didn't use a password. It was introduced in version 1.34, and fixed in version 2.48. The bug was discovered on 30 May 2008 and fixed the same day. (CVE-2008-0169)

I recommend upgrading to 2.48 immediatly if your wiki allows both password and openid logins.

## Malformed UTF-8 DOS

Feeding ikiwiki page sources containing certian forms of malformed UTF-8 can cause it to crash. This can potentially be used for a denial of service attack.

intrigeri discovered this problem on 12 Nov 2008 and a patch put in place later that day, in version 2.70. The fix was backported to testing as version 2.53.3, and to stable as version 1.33.7.

## Insufficient blacklisting in teximg plugin

Josh Triplett discovered on 28 Aug 2009 that the teximg plugin's blacklisting of insecure TeX commands was insufficient; it could be bypassed and used to read arbitrary files. This was fixed by enabling TeX configuration options that disallow unsafe TeX commands. The fix was released on 30 Aug 2009 in version 3.1415926, and was backported to stable in version 2.53.4. If you use the teximg plugin, I recommend upgrading. (CVE-2009-2944)

## javascript insertion via svg uris

Ivan Shmakov pointed out that the htmlscrubber allowed `data:image/*` urls, including `data:image/svg+xml`. But svg can contain javascript, so that is unsafe.

This hole was discovered on 12 March 2010 and fixed the same day with the release of ikiwiki 3.20100312. A fix was also backported to Debian etch, as version 2.53.5. I recommend upgrading to one of these versions if your wiki can be edited by third parties.

## javascript insertion via insufficient htmlscrubbing of comments

Kevin Riggle noticed that it was not possible to configure `htmlscrubber_skip` to scrub comments while leaving unscubbed the text of eg, blog posts. Confusingly, setting it to " and !comment()" did not scrub comments.

Additionally, it was discovered that comments' html was never scrubbed during preview or moderation of comments with such a configuration.

These problems were discovered on 12 November 2010 and fixed the same hour with the release of ikiwiki 3.20101112. (CVE-2010-1673)

## javascript insertion via insufficient checking in comments

Dave B noticed that attempting to comment on an illegal page name could be used for an XSS attack.

This hole was discovered on 22 Jan 2011 and fixed the same day with the release of ikiwiki 3.20110122. A fix was backported to Debian squeeze, as version 3.20100815.5. An upgrade is recommended for sites with the comments plugin enabled. (CVE-2011-0428)

## possible javascript insertion via insufficient htmlscrubbing of alternate stylesheets

Giuseppe Bilotta noticed that 'meta stylesheet` directives allowed anyone who could upload a malicious stylesheet to a site to add it to a page as an alternate stylesheet, or replacing the default stylesheet.

This hole was discovered on 28 Mar 2011 and fixed the same hour with the release of ikiwiki 3.20110328. A fix was backported to Debian squeeze, as version 3.20100815.6. An upgrade is recommended for sites that have untrusted committers, or have the attachments plugin enabled. (CVE-2011-1401)

## tty hijacking via ikiwiki-mass-rebuild

Ludwig Nussel discovered a way for users to hijack root's tty when ikiwiki-mass-rebuild was run. Additionally, there was some potential for information disclosure via symlinks. (CVE-2011-1408)

This hole was discovered on 8 June 2011 and fixed the same day with the release of ikiwiki 3.20110608. Note that the fix is dependant on a version of su that has a similar hole fixed. Version 4.1.5 of the shadow package contains the fixed su; Debian bug #628843 tracks fixing the hole in Debian. An upgrade is a must for any sites that have `ikiwiki-update-wikilist` installed suid (not the default), and whose admins run `ikiwiki-mass-rebuild`.

## javascript insertion via meta tags

Raúl Benencia discovered an additional XSS exposure in the meta plugin. (CVE-2012-0220)

This hole was discovered on 16 May 2012 and fixed the same day with the release of ikiwiki 3.20120516. A fix was backported to Debian squeeze, as version 3.20100815.9. An upgrade is recommended for all sites.

## XSS via openid selector

Raghav Bisht discovered this XSS in the openid selector. (CVE-2015-2793)

The hole was reported on March 24th, a fix was developed on March 27th, and the fixed version 3.20150329 was released on the 29th. A fix was backported to Debian jessie as version 3.20141016.2 and to Debian wheezy as version 3.20120629.2. An upgrade is recommended for sites using CGI and openid.

## XSS via error messages

CGI error messages did not escape HTML meta-characters, potentially allowing an attacker to carry out cross-site scripting by directing a user to a URL that would result in a crafted ikiwiki error message. This was discovered on 4 May by the ikiwiki developers, and the fixed version 3.20160506 was released on 6 May. The same fixes were backported to Debian 8 "jessie" in version 3.20141016.3. A backport to Debian 7 "wheezy" is in progress.

An upgrade is recommended for sites using the CGI. (CVE-2016-4561, OVE-20160505-0012)

## ImageMagick CVE-2016-3714 ("ImageTragick")

ikiwiki 3.20160506 and 3.20141016.3 attempt to mitigate CVE-2016-3714, and any future ImageMagick vulnerabilities that resemble it, by restricting the image formats that the img directive is willing to resize. An upgrade is recommended for sites where an untrusted user is able to attach images. Upgrading ImageMagick to a version where CVE-2016-3714 has been fixed is also recommended, but at the time of writing no such version is available.

## Perl CVE-2016-1238 (current working directory in search path)

ikiwiki 3.20160728 attempts to mitigate CVE-2016-1238 by removing `'.'` from the Perl library search path. An attacker with write access to ikiwiki's current working directory could potentially use this vulnerability to execute arbitrary Perl code. An upgrade is recommended for sites where an untrusted user is able to attach files with arbitrary names and/or run a setuid ikiwiki wrapper with a working directory of their choice.

## Editing restriction bypass for git revert

intrigeri discovered that a web or git user could revert a change to a page they are not allowed to edit, if the change being reverted was made before the page was moved from a location where that user had permission to edit it. For example, if a file is moved from `drafts/policy.mdwn` (editable by less-trusted users) to `policy.mdwn` (only editable by more-trusted users), a less-trusted user could revert a change that was made to `drafts/policy.mdwn` prior to that move, and it would result in `policy.mdwn` being altered.

This affects sites with the `git` VCS and the `recentchanges` plugin, which are both used in most ikiwiki installations.

This bug was reported on 2016-12-17. A partially fixed version 3.20161219 was released on 2016-12-19, but the solution used in that version was not effective with git versions older than 2.8.0. A more complete fix was released on 2016-12-29 in version 3.20161229, with fixes backported to Debian 8 in version 3.20141016.4.

(CVE-2016-10026 represents the original vulnerability. CVE-2016-9645/OVE-20161226-0002 represents the vulnerability in 3.20161219 caused by the incomplete fix.)

## Commit metadata forgery via CGI::FormBuilder context-dependent APIs

When CGI::FormBuilder->field("foo") is called in list context (and in particular in the arguments to a subroutine that takes named arguments), it can return zero or more values for foo from the CGI request, rather than the expected single value. This breaks the usual Perl parsing convention for named arguments, similar to CVE-2014-1572 in Bugzilla (which was caused by a similar API design issue in CGI.pm).

In ikiwiki, this appears to have been exploitable in two places, both of them relatively minor:

- in the comments plugin, an attacker who was able to post a comment could give it a user-specified author and author-URL even if the wiki configuration did not allow for that, by crafting multiple values for other fields
- in the editpage plugin, an attacker who was able to edit a page could potentially forge commit authorship (attribute their edit to someone else) by crafting multiple values for the rcsinfo field

This was fixed in ikiwiki 3.20161229, with fixes backported to Debian 8 in version 3.20141016.4.

(CVE-2016-9646/OVE-20161226-0001)

## Authentication bypass via repeated parameters

The ikiwiki maintainers discovered further flaws similar to CVE-2016-9646 in the passwordauth plugin's use of CGI::FormBuilder, with a more serious impact:

- An attacker who can log in to a site with a password can log in as a different and potentially more privileged user.
- An attacker who can create a new account can set arbitrary fields in the user database for that account.

This was fixed in ikiwiki 3.20170111, with fixes backported to Debian 8 in version 3.20141016.4.

(CVE-2017-0356/OVE-20170111-0001)

## Server-side request forgery via aggregate plugin

The ikiwiki maintainers discovered that the aggregate plugin did not use LWPx::ParanoidAgent. On sites where the aggregate plugin is enabled, authorized wiki editors could tell ikiwiki to fetch potentially undesired URIs even if LWPx::ParanoidAgent was installed:

- local files via `file:` URIs
- other URI schemes that might be misused by attackers, such as `gopher:`
- hosts that resolve to loopback IP addresses (127.x.x.x)
- hosts that resolve to RFC 1918 IP addresses (192.168.x.x etc.)

This could be used by an attacker to publish information that should not have been accessible, cause denial of service by requesting "tarpit" URIs that are slow to respond, or cause undesired side-effects if local web servers implement "unsafe" GET requests. (CVE-2019-9187)

Additionally, if the LWPx::ParanoidAgent module was not installed, the blogspam, openid and pinger plugins would fall back to LWP, which is susceptible to similar attacks. This is unlikely to be a practical problem for the blogspam plugin because the URL it requests is under the control of the wiki administrator, but the openid plugin can request URLs controlled by unauthenticated remote users, and the pinger plugin can request URLs controlled by authorized wiki editors.

This is addressed in ikiwiki 3.20190228 as follows, with the same fixes backported to Debian 9 in version 3.20170111.1:

- URI schemes other than `http:` and `https:` are not accepted, preventing access to `file:`, `gopher:`, etc.

- If a proxy is configured in the ikiwiki setup file, it is used for all outgoing `http:` and `https:` requests. In this case the proxy is responsible for blocking any requests that are undesired, including loopback or RFC 1918 addresses.

- If a proxy is not configured, and LWPx::ParanoidAgent is installed, it will be used. This prevents loopback and RFC 1918 IP addresses, and sets a timeout to avoid denial of service via "tarpit" URIs.

- Otherwise, the ordinary LWP user-agent will be used. This allows requests to loopback and RFC 1918 IP addresses, and has less robust timeout behaviour. We are not treating this as a vulnerability: if this behaviour is not acceptable for your site, please make sure to install LWPx::ParanoidAgent or disable the affected plugins.