-Let's do an ikiwiki security analysis..
+Let's do an ikiwiki security analysis.
-If you are using ikiwiki to render pages that only you can edit, 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 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.
-## html attacks
+[[toc levels=2]]
-ikiwiki does not attempt to do any santization of the html on the wiki.
-MarkDown allows embedding of arbitrary html into a markdown document. If
-you let anyone else edit files on the wiki, then anyone can have fun exploiting
-the web browser bug of the day. This type of attack is typically referred
-to as an XSS attack ([google](http://www.google.com/search?q=xss+attack)).
+----
-## image files etc attacks
+# 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 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.
+
+----
+
+# 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, etc. If these files exploit
-security holes in the browser of someone who's viewing the wiki, that can
-be a security problem.
+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.
-## exploting ikiwiki with bad content
+Of course nobody else seems to worry about this in other wikis, so should we?
-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;
-the only data that is not subject to full taint checking is the names of
-files, and filenames are sanitised.
+Currently only people with direct commit access can upload such files
+(and if you wanted to you could block that with a 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.
-## cgi scripts
+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.
-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, so
-hopefully your web server will not run it.
+## 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. [[ikiwiki.setup]] is *not*
+used as the setup file for this wiki, BTW.
+
+## 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
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.
-## --gen-wrapper might generate insecure wrappers
+----
+
+# 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.
-ikiwiki --gen-wrapper is intended to generate a wrapper program that
+## 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 script is made suid, then any bugs in this wrapper would be
-security holes. The wrapper is written as securely as I know how 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.
+
+## 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..
+
+## 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 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.
+
+## XSS holes in CGI output
+
+ikiwiki has not yet 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 [[plugins/template]] plugin is enabled, users can modify templates
+like any other part of the wiki. This assumes that HTML::Template is secure
+when used with untrusted/malicious templates. (Note that includes are not
+allowed, so that's not a problem.)
+
+----
+
+# 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. 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
+[[plugins/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](http://bugs.debian.org/378411) does not
+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.
+
+## 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. Some
+urls specifyable by the meta plugin could also theoretically have been used
+to inject javascript; this was also blocked.
+
+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.