3.20161229.1~bpo8+1

[git.ikiwiki.info.git] / doc / security.mdwn

diff --git a/doc/security.mdwn b/doc/security.mdwn
index 9d7702dde3a09053fb09c27a9553a8829f4068e6..823f5ef88297fcea7b706a74cd8f6639c8ac7e6b 100644 (file)
--- a/doc/security.mdwn
+++ b/doc/security.mdwn
@@ -1,11 +1,18 @@
-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.
 
 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]] (<joey@kitenet.net>),
+[[Simon McVittie|smcv]] (<smcv@debian.org>)
+and [[Amitai Schleier|schmonz]] (<schmonz-web-ikiwiki@schmonz.com>).
+
+[[!toc levels=2]]
+

 ----
 
 # Probable holes
 ----
 
 # Probable holes


@@ -16,12 +23,12 @@ _(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
 
 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 certian user.
+this would be to limit web commits to those done by a certain user.

 
 ## other stuff to look at
 
 
 ## other stuff to look at
 

-I need to audit the git backend a bit, and have been meaning to
-see if any CRLF injection type things can be done in the CGI code.
+I have been meaning to see if any CRLF injection type things can be
+done in the CGI code.

 
 ----
 
 
 ----
 


@@ -39,32 +46,39 @@ 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?
 
 
 Of course nobody else seems to worry about this in other wikis, so should we?
 

-Currently only people with direct svn commit access can upload such files
-(and if you wanted to you could block that with a svn pre-commit hook).
-Users with only web commit access are limited to editing pages as ikiwiki
-doesn't support file uploads from browsers (yet), so they can't exploit
-this.
+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
 
 
 ## multiple accessors of wiki directory
 

-If multiple people can 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.
+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 write to those directories.
+So it's best if only one person can ever directly write to those directories.

 
 ## setup files
 
 
 ## setup files
 

-Setup files are not safe to keep in subversion with the rest of the wiki.
-Just don't do it. [[ikiwiki.setup]] is *not* used as the setup file for
-this wiki, BTW.
+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 svn commits
+## 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 direct to svn can bypass this. This is by
-design, although a subversion pre-commit hook could be used to prevent
-editing of locked pages when using subversion, if you really need to.
+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
 
 
 ## web server attacks
 


@@ -78,7 +92,7 @@ they can try to use this to exploit your web server.
 
 _(AKA, the assumptions that will be the root of most security holes...)_
 
 
 _(AKA, the assumptions that will be the root of most security holes...)_
 

-## exploting ikiwiki with bad content
+## 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.
 
 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.


@@ -96,12 +110,12 @@ your web server will not run it.
 
 ## suid wrappers
 
 
 ## suid wrappers
 

-ikiwiki --wrapper is intended to generate a wrapper program that
+`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.
 
 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 script is made suid, then any bugs in this wrapper would be
+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.
 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.


@@ -109,9 +123,13 @@ been no problem yet.
 ## shell exploits
 
 ikiwiki does not expose untrusted data to the shell. In fact it doesn't use
 ## shell exploits
 
 ikiwiki does not expose untrusted data to the shell. In fact it doesn't use

-system() at all, and the only use of backticks is on data supplied by the
-wiki admin and untainted filenames. And it runs with taint checks on of
-course..
+`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](http://bugs.debian.org/411786) in perl, taint checking
+is currently disabled for production builds of ikiwiki.

 
 ## cgi data security
 
 
 ## cgi data security
 


@@ -120,8 +138,8 @@ 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 "/"
 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/". Annoyingly ad-hoc, this kind of code is where
-security holes breed. It needs a test suite at the very least.
+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
 
 
 ## CGI::Session security
 


@@ -132,15 +150,15 @@ file not be world readable.
 
 ## cgi password security
 
 
 ## cgi password security
 

-Login to the wiki 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.
+Login to the wiki using [[plugins/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 [[plugins/openid]] is a potentially better option.

 
 ## XSS holes in CGI output
 
 
 ## XSS holes in CGI output
 

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


@@ -149,10 +167,26 @@ closed though.
 
 ## HTML::Template security
 
 
 ## HTML::Template security
 

-If the [[plugins/template]] plugin is enabled, users can modify templates
-like any other part of the wiki. This assumes that HTML::Template is secure
+If the [[plugins/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
 when used with untrusted/malicious templates. (Note that includes are not

-allowed, so that's not a problem.)
+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 [[plugins/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.

 
 ----
 
 
 ----
 


@@ -188,13 +222,13 @@ 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
 
 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 at the wrong time to race
-another ikiwiki. So only attackers who can write to the working copy on
-their own can race it.
+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
 
 
 ## symlink + cgi attacks
 

-Similarly, a svn commit of a symlink could be made, ikiwiki ignores 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
 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


@@ -256,3 +290,308 @@ seem to affect our use, since the data is not encoded as utf-8 at that
 point. #[378412](http://bugs.debian.org/378412) could affect us, although it
 doesn't seem very exploitable. It has a simple fix, and has been fixed in
 Debian unstable.
 point. #[378412](http://bugs.debian.org/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 CVE-2008-0809]]) Some urls specifyable by the meta plugin could also
+theoretically have been used to inject javascript; this was also blocked
+([[!cve 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 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 [[plugins/passwordauth]] plugin, I recommend upgrading to
+ikiwiki 2.48, installing the [[!cpan 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 [[plugins/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](http://bugs.debian.org/483770) was
+discovered on 30 May 2008 and fixed the same day. ([[!cve 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 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 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 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 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 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; [[!debbug 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 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 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 CVE-2016-4561]], OVE-20160505-0012)
+
+## ImageMagick CVE-2016–3714 ("ImageTragick")
+
+ikiwiki 3.20160506 and 3.20141016.3 attempt to mitigate
+[[!cve CVE-2016-3714]], and any
+future ImageMagick vulnerabilities that resemble it, by restricting the
+image formats that the [[ikiwiki/directive/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 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.
+A backport to Debian 8 'jessie' is in progress.
+
+([[!cve CVE-2016-10026]] represents the original vulnerability.
+[[!cve 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. A backport to Debian 8
+'jessie' is in progress.
+
+([[!cve CVE-2016-9646]]/OVE-20161226-0001)