1 Let's do an ikiwiki security analysis.
3 If you are using ikiwiki to render pages that only you can edit, do not
4 generate any wrappers, and do not use the cgi, then there are no more
5 security issues with this program than with cat(1). If, however, you let
6 others edit pages in your wiki, then some possible security issues do need
15 _(The list of things to fix.)_
19 Anyone with direct commit access can forge "web commit from foo" and
20 make it appear on [[RecentChanges]] like foo committed. One way to avoid
21 this would be to limit web commits to those done by a certain user.
23 ## other stuff to look at
25 I need to audit the git backend a bit, and have been meaning to
26 see if any CRLF injection type things can be done in the CGI code.
34 ## image file etc attacks
36 If it enounters a file type it does not understand, ikiwiki just copies it
37 into place. So if you let users add any kind of file they like, they can
38 upload images, movies, windows executables, css files, etc (though not html
39 files). If these files exploit security holes in the browser of someone
40 who's viewing the wiki, that can be a security problem.
42 Of course nobody else seems to worry about this in other wikis, so should we?
44 Currently only people with direct commit access can upload such files
45 (and if you wanted to you could block that with a pre-commit hook).
46 Users with only web commit access are limited to editing pages as ikiwiki
47 doesn't support file uploads from browsers (yet), so they can't exploit
50 It is possible to embed an image in a page edited over the web, by using
51 `img src="data:image/png;"`. Ikiwiki's htmlscrubber only allows `data:`
52 urls to be used for `image/*` mime types. It's possible that some broken
53 browser might ignore the mime type and if the data provided is not an
54 image, instead run it as javascript, or something evil like that. Hopefully
55 not many browsers are that broken.
57 ## multiple accessors of wiki directory
59 If multiple people can directly write to the source directory ikiwiki is
60 using, or to the destination directory it writes files to, then one can
61 cause trouble for the other when they run ikiwiki through symlink attacks.
63 So it's best if only one person can ever directly write to those directories.
67 Setup files are not safe to keep in the same revision control repository
68 with the rest of the wiki. Just don't do it. [[ikiwiki.setup]] is *not*
69 used as the setup file for this wiki, BTW.
71 ## page locking can be bypassed via direct commits
73 A locked page can only be edited on the web by an admin, but anyone who is
74 allowed to commit directly to the repository can bypass this. This is by
75 design, although a pre-commit hook could be used to prevent editing of
76 locked pages, if you really need to.
80 If your web server does any parsing of special sorts of files (for example,
81 server parsed html files), then if you let anyone else add files to the wiki,
82 they can try to use this to exploit your web server.
88 _(AKA, the assumptions that will be the root of most security holes...)_
90 ## exploiting ikiwiki with bad content
92 Someone could add bad content to the wiki and hope to exploit ikiwiki.
93 Note that ikiwiki runs with perl taint checks on, so this is unlikely.
95 One fun thing in ikiwiki is its handling of a PageSpec, which involves
96 translating it into perl and running the perl. Of course, this is done
97 *very* carefully to guard against injecting arbitrary perl code.
99 ## publishing cgi scripts
101 ikiwiki does not allow cgi scripts to be published as part of the wiki. Or
102 rather, the script is published, but it's not marked executable (except in
103 the case of "destination directory file replacement" below), so hopefully
104 your web server will not run it.
108 ikiwiki --wrapper is intended to generate a wrapper program that
109 runs ikiwiki to update a given wiki. The wrapper can in turn be made suid,
110 for example to be used in a [[post-commit]] hook by people who cannot write
111 to the html pages, etc.
113 If the wrapper script is made suid, then any bugs in this wrapper would be
114 security holes. The wrapper is written as securely as I know how, is based
115 on code that has a history of security use long before ikiwiki, and there's
120 ikiwiki does not expose untrusted data to the shell. In fact it doesn't use
121 system() at all, and the only use of backticks is on data supplied by the
122 wiki admin and untainted filenames. And it runs with taint checks on of
127 When ikiwiki runs as a cgi to edit a page, it is passed the name of the
128 page to edit. It has to make sure to sanitise this page, to prevent eg,
129 editing of ../../../foo, or editing of files that are not part of the wiki,
130 such as subversion dotfiles. This is done by sanitising the filename
131 removing unallowed characters, then making sure it doesn't start with "/"
132 or contain ".." or "/.svn/", etc. Annoyingly ad-hoc, this kind of code is
133 where security holes breed. It needs a test suite at the very least.
135 ## CGI::Session security
137 I've audited this module and it is massively insecure by default. ikiwiki
138 uses it in one of the few secure ways; by forcing it to write to a
139 directory it controls (and not /tmp) and by setting a umask that makes the
140 file not be world readable.
142 ## cgi password security
144 Login to the wiki involves sending a password in cleartext over the net.
145 Cracking the password only allows editing the wiki as that user though.
146 If you care, you can use https, I suppose. If you do use https either for
147 all of the wiki, or just the cgi access, then consider using the sslcookie
150 ## XSS holes in CGI output
152 ikiwiki has not yet been audited to ensure that all cgi script input/output
153 is sanitised to prevent XSS attacks. For example, a user can't register
154 with a username containing html code (anymore).
156 It's difficult to know for sure if all such avenues have really been
159 ## HTML::Template security
161 If the [[plugins/template]] plugin is enabled, users can modify templates
162 like any other part of the wiki. This assumes that HTML::Template is secure
163 when used with untrusted/malicious templates. (Note that includes are not
164 allowed, so that's not a problem.)
170 The security of [[plugins]] depends on how well they're written and what
171 external tools they use. The plugins included in ikiwiki are all held to
172 the same standards as the rest of ikiwiki, but with that said, here are
173 some security notes for them.
175 * The [[plugins/img]] plugin assumes that imagemagick/perlmagick are secure
176 from malformed image attacks. Imagemagick has had security holes in the
177 past. To be able to exploit such a hole, a user would need to be able to
178 upload images to the wiki.
184 _(Unless otherwise noted, these were discovered and immediately fixed by the
185 ikiwiki developers.)_
187 ## destination directory file replacement
189 Any file in the destination directory that is a valid page filename can be
190 replaced, even if it was not originally rendered from a page. For example,
191 ikiwiki.cgi could be edited in the wiki, and it would write out a
192 replacement. File permission is preseved. Yipes!
194 This was fixed by making ikiwiki check if the file it's writing to exists;
195 if it does then it has to be a file that it's aware of creating before, or
196 it will refuse to create it.
198 Still, this sort of attack is something to keep in mind.
202 Could a committer trick ikiwiki into following a symlink and operating on
203 some other tree that it shouldn't? svn supports symlinks, so one can get
204 into the repo. ikiwiki uses File::Find to traverse the repo, and does not
205 tell it to follow symlinks, but it might be possible to race replacing a
206 directory with a symlink and trick it into following the link.
208 Also, if someone checks in a symlink to /etc/passwd, ikiwiki would read and
209 publish that, which could be used to expose files a committer otherwise
212 To avoid this, ikiwiki will skip over symlinks when scanning for pages, and
213 uses locking to prevent more than one instance running at a time. The lock
214 prevents one ikiwiki from running a svn up/git pull/etc at the wrong time
215 to race another ikiwiki. So only attackers who can write to the working
216 copy on their own can race it.
218 ## symlink + cgi attacks
220 Similarly, a commit of a symlink could be made, ikiwiki ignores it
221 because of the above, but the symlink is still there, and then you edit the
222 page from the web, which follows the symlink when reading the page
223 (exposing the content), and again when saving the changed page (changing
226 This was fixed for page saving by making ikiwiki refuse to write to files
227 that are symlinks, or that are in subdirectories that are symlinks,
228 combined with the above locking.
230 For page editing, it's fixed by ikiwiki checking to make sure that it
231 already has found a page by scanning the tree, before loading it for
232 editing, which as described above, also is done in a way that avoids
235 ## underlaydir override attacks
237 ikiwiki also scans an underlaydir for pages, this is used to provide stock
238 pages to all wikis w/o needing to copy them into the wiki. Since ikiwiki
239 internally stores only the base filename from the underlaydir or srcdir,
240 and searches for a file in either directory when reading a page source,
241 there is the potential for ikiwiki's scanner to reject a file from the
242 srcdir for some reason (such as it being contained in a directory that is
243 symlinked in), find a valid copy of the file in the underlaydir, and then
244 when loading the file, mistakenly load the bad file from the srcdir.
246 This attack is avoided by making ikiwiki refuse to add any files from the
247 underlaydir if a file also exists in the srcdir with the same name.
249 ## multiple page source issues
251 Note that I previously worried that underlay override attacks could also be
252 accomplished if ikiwiki were extended to support other page markup
253 languages besides markdown. However, a closer look indicates that this is
254 not a problem: ikiwiki does preserve the file extension when storing the
255 source filename of a page, so a file with another extension that renders to
256 the same page name can't bypass the check. Ie, ikiwiki won't skip foo.rst
257 in the srcdir, find foo.mdwn in the underlay, decide to render page foo and
258 then read the bad foo.mdwn. Instead it will remember the .rst extension and
259 only render a file with that extension.
261 ## XSS attacks in page content
263 ikiwiki supports protecting users from their own broken browsers via the
264 [[plugins/htmlscrubber]] plugin, which is enabled by default.
268 It's was possible to force a whole series of svn commits to appear to
269 have come just before yours, by forging svn log output. This was
270 guarded against by using svn log --xml.
272 ikiwiki escapes any html in svn commit logs to prevent other mischief.
276 XML::Parser is used by the aggregation plugin, and has some security holes.
277 Bug #[378411](http://bugs.debian.org/378411) does not
278 seem to affect our use, since the data is not encoded as utf-8 at that
279 point. #[378412](http://bugs.debian.org/378412) could affect us, although it
280 doesn't seem very exploitable. It has a simple fix, and has been fixed in
285 Various directives that cause one page to be included into another could
286 be exploited to DOS the wiki, by causing a loop. Ikiwiki has always guarded
287 against this one way or another; the current solution should detect all
288 types of loops involving preprocessor directives.
290 ## Online editing of existing css and images
292 A bug in ikiwiki allowed the web-based editor to edit any file that was in
293 the wiki, not just files that are page sources. So an attacker (or a
294 genuinely helpful user, which is how the hole came to light) could edit
295 files like style.css. It is also theoretically possible that an attacker
296 could have used this hole to edit images or other files in the wiki, with
297 some difficulty, since all editing would happen in a textarea.
299 This hole was discovered on 10 Feb 2007 and fixed the same day with the
300 release of ikiwiki 1.42. A fix was also backported to Debian etch, as
301 version 1.33.1. I recommend upgrading to one of these versions if your wiki
304 ## html insertion via title
306 Missing html escaping of the title contents allowed a web-based editor to
307 insert arbitrary html inside the title tag of a page. Since that part of
308 the page is not processed by the htmlscrubber, evil html could be injected.
310 This hole was discovered on 21 March 2007 and fixed the same day (er, hour)
311 with the release of ikiwiki 1.46. A fix was also backported to Debian etch,
312 as version 1.33.2. I recommend upgrading to one of these versions if your
313 wiki allows web editing or aggregates feeds.
315 ## javascript insertion via meta tags
317 It was possible to use the meta plugin's meta tags to insert arbitrary
318 url contents, which could be used to insert stylesheet information
319 containing javascript. This was fixed by sanitising meta tags.
321 This hole was discovered on 21 March 2007 and fixed the same day
322 with the release of ikiwiki 1.47. A fix was also backported to Debian etch,
323 as version 1.33.3. I recommend upgrading to one of these versions if your
324 wiki can be edited by third parties.
326 ## insufficient checking for symlinks in srcdir path
328 Ikiwiki did not check if path to the srcdir to contained a symlink. If an
329 attacker had commit access to the directories in the path, they could
330 change it to a symlink, causing ikiwiki to read and publish files that were
331 not intended to be published. (But not write to them due to other checks.)
333 In most configurations, this is not exploitable, because the srcdir is
334 checked out of revision control, but the directories leading up to it are
335 not. Or, the srcdir is a single subdirectory of a project in revision
336 control (ie, `ikiwiki/doc`), and if the subdirectory were a symlink,
337 ikiwiki would still typically not follow it.
339 There are at least two configurations where this is exploitable:
341 * If the srcdir is a deeper subdirectory of a project. For example if it is
342 `project/foo/doc`, an an attacker can replace `foo` with a symlink to a
343 directory containing a `doc` directory (not a symlink), then ikiwiki
344 would follow the symlink.
345 * If the path to the srcdir in ikiwiki's configuration ended in "/",
346 and the srcdir is a single subdirectory of a project, (ie,
347 `ikiwiki/doc/`), the srcdir could be a symlink and ikiwiki would not
350 This security hole was discovered on 26 November 2007 and fixed the same
351 day with the release of ikiwiki 2.14. I recommend upgrading to this version
352 if your wiki can be committed to by third parties. Alternatively, don't use
353 a trailing slash in the srcdir, and avoid the (unusual) configurations that
354 allow the security hole to be exploited.
356 ## javascript insertion via uris
358 The htmlscrubber did not block javascript in uris. This was fixed by adding
359 a whitelist of valid uri types, which does not include javascript.
360 ([[cve CVE-2008-0809]]) Some urls specifyable by the meta plugin could also
361 theoretically have been used to inject javascript; this was also blocked
362 ([[cve CVE-2008-0808]]).
364 This hole was discovered on 10 February 2008 and fixed the same day
365 with the release of ikiwiki 2.31.1. (And a few subsequent versions..)
366 A fix was also backported to Debian etch, as version 1.33.4. I recommend
367 upgrading to one of these versions if your wiki can be edited by third