Let's do an ikiwiki security analysis.
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.
- Probable holes
- Potential gotchas
- Hopefully non-holes
- Fixed holes
- destination directory file replacement
- symlink attacks
- symlink + cgi attacks
- underlaydir override attacks
- multiple page source issues
- XSS attacks in page content
- svn commit logs
- include loops
- Online editing of existing css and images
- html insertion via title
- insufficient checking for symlinks in srcdir path
- Cross Site Request Forging
- Cleartext passwords
- Empty password security hole
- Malformed UTF-8 DOS
- Insufficient blacklisting in teximg plugin
- tty hijacking via ikiwiki-mass-rebuild
- XSS via openid selector
- XSS via error messages
- ImageMagick CVE-2016–3714 ("ImageTragick")
(The list of things to fix.)
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.
I have been meaning to see if any CRLF injection type things can be done in the CGI code.
(Things not to do.)
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
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
not many browsers are that broken.
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 are not safe to keep in the same revision control repository with the rest of the wiki. Just don't do it.
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.
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.
(AKA, the assumptions that will be the root of most security holes...)
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.
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.
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.
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.
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.
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.
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.
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.
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.)
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.
(Unless otherwise noted, these were discovered and immediately fixed by the ikiwiki developers.)
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.
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.
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.
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.
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.
ikiwiki supports protecting users from their own broken browsers via the htmlscrubber plugin, which is enabled by default.
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 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.
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.
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.
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.
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.
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
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
foowith a symlink to a directory containing a
docdirectory (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.
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 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.
Until version 2.48, ikiwiki stored passwords in cleartext in the
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.
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.
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.
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)
Ivan Shmakov pointed out that the htmlscrubber allowed
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.
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
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)
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)
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)
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
installed suid (not the default), and whose admins run
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.
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.
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)
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.