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 People with direct commit access can upload such files
45 (and if you wanted to you could block that with a pre-commit hook).
47 The attachments plugin is not enabled by default. If you choose to
48 enable it, you should make use of its powerful abilities to filter allowed
49 types of attachments, and only let trusted users upload.
51 It is possible to embed an image in a page edited over the web, by using
52 `img src="data:image/png;"`. Ikiwiki's htmlscrubber only allows `data:`
53 urls to be used for `image/*` mime types. It's possible that some broken
54 browser might ignore the mime type and if the data provided is not an
55 image, instead run it as javascript, or something evil like that. Hopefully
56 not many browsers are that broken.
58 ## multiple accessors of wiki directory
60 If multiple people can directly write to the source directory ikiwiki is
61 using, or to the destination directory it writes files to, then one can
62 cause trouble for the other when they run ikiwiki through symlink attacks.
64 So it's best if only one person can ever directly write to those directories.
68 Setup files are not safe to keep in the same revision control repository
69 with the rest of the wiki. Just don't do it.
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(3)` at all, and the only use of backticks is on data supplied by the
122 wiki admin and untainted filenames.
124 Ikiwiki was developed and used for a long time with perl's taint checking
125 turned on as a second layer of defense against shell and other exploits. Due
126 to a strange [bug](http://bugs.debian.org/411786) in perl, taint checking
127 is currently disabled for production builds of ikiwiki.
131 When ikiwiki runs as a cgi to edit a page, it is passed the name of the
132 page to edit. It has to make sure to sanitise this page, to prevent eg,
133 editing of ../../../foo, or editing of files that are not part of the wiki,
134 such as subversion dotfiles. This is done by sanitising the filename
135 removing unallowed characters, then making sure it doesn't start with "/"
136 or contain ".." or "/.svn/", etc. Annoyingly ad-hoc, this kind of code is
137 where security holes breed. It needs a test suite at the very least.
139 ## CGI::Session security
141 I've audited this module and it is massively insecure by default. ikiwiki
142 uses it in one of the few secure ways; by forcing it to write to a
143 directory it controls (and not /tmp) and by setting a umask that makes the
144 file not be world readable.
146 ## cgi password security
148 Login to the wiki using [[plugins/passwordauth]] involves sending a password
149 in cleartext over the net. Cracking the password only allows editing the wiki
150 as that user though. If you care, you can use https, I suppose. If you do use
151 https either for all of the wiki, or just the cgi access, then consider using
152 the sslcookie option. Using [[plugins/openid]] is a potentially better option.
154 ## XSS holes in CGI output
156 ikiwiki has been audited to ensure that all cgi script input/output
157 is sanitised to prevent XSS attacks. For example, a user can't register
158 with a username containing html code (anymore).
160 It's difficult to know for sure if all such avenues have really been
163 ## HTML::Template security
165 If the [[plugins/template]] plugin is enabled, all users can modify templates
166 like any other part of the wiki. Some trusted users can modify templates
167 without it too. This assumes that HTML::Template is secure
168 when used with untrusted/malicious templates. (Note that includes are not
175 The security of [[plugins]] depends on how well they're written and what
176 external tools they use. The plugins included in ikiwiki are all held to
177 the same standards as the rest of ikiwiki, but with that said, here are
178 some security notes for them.
180 * The [[plugins/img]] plugin assumes that imagemagick/perlmagick are secure
181 from malformed image attacks. Imagemagick has had security holes in the
182 past. To be able to exploit such a hole, a user would need to be able to
183 upload images to the wiki.
189 _(Unless otherwise noted, these were discovered and immediately fixed by the
190 ikiwiki developers.)_
192 ## destination directory file replacement
194 Any file in the destination directory that is a valid page filename can be
195 replaced, even if it was not originally rendered from a page. For example,
196 ikiwiki.cgi could be edited in the wiki, and it would write out a
197 replacement. File permission is preseved. Yipes!
199 This was fixed by making ikiwiki check if the file it's writing to exists;
200 if it does then it has to be a file that it's aware of creating before, or
201 it will refuse to create it.
203 Still, this sort of attack is something to keep in mind.
207 Could a committer trick ikiwiki into following a symlink and operating on
208 some other tree that it shouldn't? svn supports symlinks, so one can get
209 into the repo. ikiwiki uses File::Find to traverse the repo, and does not
210 tell it to follow symlinks, but it might be possible to race replacing a
211 directory with a symlink and trick it into following the link.
213 Also, if someone checks in a symlink to /etc/passwd, ikiwiki would read and
214 publish that, which could be used to expose files a committer otherwise
217 To avoid this, ikiwiki will skip over symlinks when scanning for pages, and
218 uses locking to prevent more than one instance running at a time. The lock
219 prevents one ikiwiki from running a svn up/git pull/etc at the wrong time
220 to race another ikiwiki. So only attackers who can write to the working
221 copy on their own can race it.
223 ## symlink + cgi attacks
225 Similarly, a commit of a symlink could be made, ikiwiki ignores it
226 because of the above, but the symlink is still there, and then you edit the
227 page from the web, which follows the symlink when reading the page
228 (exposing the content), and again when saving the changed page (changing
231 This was fixed for page saving by making ikiwiki refuse to write to files
232 that are symlinks, or that are in subdirectories that are symlinks,
233 combined with the above locking.
235 For page editing, it's fixed by ikiwiki checking to make sure that it
236 already has found a page by scanning the tree, before loading it for
237 editing, which as described above, also is done in a way that avoids
240 ## underlaydir override attacks
242 ikiwiki also scans an underlaydir for pages, this is used to provide stock
243 pages to all wikis w/o needing to copy them into the wiki. Since ikiwiki
244 internally stores only the base filename from the underlaydir or srcdir,
245 and searches for a file in either directory when reading a page source,
246 there is the potential for ikiwiki's scanner to reject a file from the
247 srcdir for some reason (such as it being contained in a directory that is
248 symlinked in), find a valid copy of the file in the underlaydir, and then
249 when loading the file, mistakenly load the bad file from the srcdir.
251 This attack is avoided by making ikiwiki refuse to add any files from the
252 underlaydir if a file also exists in the srcdir with the same name.
254 ## multiple page source issues
256 Note that I previously worried that underlay override attacks could also be
257 accomplished if ikiwiki were extended to support other page markup
258 languages besides markdown. However, a closer look indicates that this is
259 not a problem: ikiwiki does preserve the file extension when storing the
260 source filename of a page, so a file with another extension that renders to
261 the same page name can't bypass the check. Ie, ikiwiki won't skip foo.rst
262 in the srcdir, find foo.mdwn in the underlay, decide to render page foo and
263 then read the bad foo.mdwn. Instead it will remember the .rst extension and
264 only render a file with that extension.
266 ## XSS attacks in page content
268 ikiwiki supports protecting users from their own broken browsers via the
269 [[plugins/htmlscrubber]] plugin, which is enabled by default.
273 It's was possible to force a whole series of svn commits to appear to
274 have come just before yours, by forging svn log output. This was
275 guarded against by using svn log --xml.
277 ikiwiki escapes any html in svn commit logs to prevent other mischief.
281 XML::Parser is used by the aggregation plugin, and has some security holes.
282 Bug #[378411](http://bugs.debian.org/378411) does not
283 seem to affect our use, since the data is not encoded as utf-8 at that
284 point. #[378412](http://bugs.debian.org/378412) could affect us, although it
285 doesn't seem very exploitable. It has a simple fix, and has been fixed in
290 Various directives that cause one page to be included into another could
291 be exploited to DOS the wiki, by causing a loop. Ikiwiki has always guarded
292 against this one way or another; the current solution should detect all
293 types of loops involving preprocessor directives.
295 ## Online editing of existing css and images
297 A bug in ikiwiki allowed the web-based editor to edit any file that was in
298 the wiki, not just files that are page sources. So an attacker (or a
299 genuinely helpful user, which is how the hole came to light) could edit
300 files like style.css. It is also theoretically possible that an attacker
301 could have used this hole to edit images or other files in the wiki, with
302 some difficulty, since all editing would happen in a textarea.
304 This hole was discovered on 10 Feb 2007 and fixed the same day with the
305 release of ikiwiki 1.42. A fix was also backported to Debian etch, as
306 version 1.33.1. I recommend upgrading to one of these versions if your wiki
309 ## html insertion via title
311 Missing html escaping of the title contents allowed a web-based editor to
312 insert arbitrary html inside the title tag of a page. Since that part of
313 the page is not processed by the htmlscrubber, evil html could be injected.
315 This hole was discovered on 21 March 2007 and fixed the same day (er, hour)
316 with the release of ikiwiki 1.46. A fix was also backported to Debian etch,
317 as version 1.33.2. I recommend upgrading to one of these versions if your
318 wiki allows web editing or aggregates feeds.
320 ## javascript insertion via meta tags
322 It was possible to use the meta plugin's meta tags to insert arbitrary
323 url contents, which could be used to insert stylesheet information
324 containing javascript. This was fixed by sanitising meta tags.
326 This hole was discovered on 21 March 2007 and fixed the same day
327 with the release of ikiwiki 1.47. A fix was also backported to Debian etch,
328 as version 1.33.3. I recommend upgrading to one of these versions if your
329 wiki can be edited by third parties.
331 ## insufficient checking for symlinks in srcdir path
333 Ikiwiki did not check if path to the srcdir to contained a symlink. If an
334 attacker had commit access to the directories in the path, they could
335 change it to a symlink, causing ikiwiki to read and publish files that were
336 not intended to be published. (But not write to them due to other checks.)
338 In most configurations, this is not exploitable, because the srcdir is
339 checked out of revision control, but the directories leading up to it are
340 not. Or, the srcdir is a single subdirectory of a project in revision
341 control (ie, `ikiwiki/doc`), and if the subdirectory were a symlink,
342 ikiwiki would still typically not follow it.
344 There are at least two configurations where this is exploitable:
346 * If the srcdir is a deeper subdirectory of a project. For example if it is
347 `project/foo/doc`, an an attacker can replace `foo` with a symlink to a
348 directory containing a `doc` directory (not a symlink), then ikiwiki
349 would follow the symlink.
350 * If the path to the srcdir in ikiwiki's configuration ended in "/",
351 and the srcdir is a single subdirectory of a project, (ie,
352 `ikiwiki/doc/`), the srcdir could be a symlink and ikiwiki would not
355 This security hole was discovered on 26 November 2007 and fixed the same
356 day with the release of ikiwiki 2.14. I recommend upgrading to this version
357 if your wiki can be committed to by third parties. Alternatively, don't use
358 a trailing slash in the srcdir, and avoid the (unusual) configurations that
359 allow the security hole to be exploited.
361 ## javascript insertion via uris
363 The htmlscrubber did not block javascript in uris. This was fixed by adding
364 a whitelist of valid uri types, which does not include javascript.
365 ([[!cve CVE-2008-0809]]) Some urls specifyable by the meta plugin could also
366 theoretically have been used to inject javascript; this was also blocked
367 ([[!cve CVE-2008-0808]]).
369 This hole was discovered on 10 February 2008 and fixed the same day
370 with the release of ikiwiki 2.31.1. (And a few subsequent versions..)
371 A fix was also backported to Debian etch, as version 1.33.4. I recommend
372 upgrading to one of these versions if your wiki can be edited by third
375 ## Cross Site Request Forging
377 Cross Site Request Forging could be used to constuct a link that would
378 change a logged-in user's password or other preferences if they clicked on
379 the link. It could also be used to construct a link that would cause a wiki
380 page to be modified by a logged-in user. ([[!cve CVE-2008-0165]])
382 These holes were discovered on 10 April 2008 and fixed the same day with
383 the release of ikiwiki 2.42. A fix was also backported to Debian etch, as
384 version 1.33.5. I recommend upgrading to one of these versions.
386 ## Cleartext passwords
388 Until version 2.48, ikiwiki stored passwords in cleartext in the `userdb`.
389 That risks exposing all users' passwords if the file is somehow exposed. To
390 pre-emtively guard against that, current versions of ikiwiki store password
391 hashes (using Eksblowfish).
393 If you use the [[plugins/passwordauth]] plugin, I recommend upgrading to
394 ikiwiki 2.48, installing the [[!cpan Authen::Passphrase]] perl module, and running
395 `ikiwiki-transition hashpassword` to replace all existing cleartext passwords
396 with strong blowfish hashes.
398 You might also consider changing to [[plugins/openid]], which does not
399 require ikiwiki deal with passwords at all, and does not involve users sending
400 passwords in cleartext over the net to log in, either.
402 ## Empty password security hole
404 This hole allowed ikiwiki to accept logins using empty passwords, to openid
405 accounts that didn't use a password. It was introduced in version 1.34, and
406 fixed in version 2.48. The [bug](http://bugs.debian.org/483770) was
407 discovered on 30 May 2008 and fixed the same day. ([[!cve CVE-2008-0169]])
409 I recommend upgrading to 2.48 immediatly if your wiki allows both password
412 ## Malformed UTF-8 DOS
414 Feeding ikiwiki page sources containing certian forms of malformed UTF-8
415 can cause it to crash. This can potentially be used for a denial of service
418 intrigeri discovered this problem on 12 Nov 2008 and a patch put in place
419 later that day, in version 2.70. The fix was backported to testing as version
420 2.53.3, and to stable as version 1.33.7.
422 ## Insufficient blacklisting in teximg plugin
424 Josh Triplett discovered on 28 Aug 2009 that the teximg plugin's
425 blacklisting of insecure TeX commands was insufficient; it could be
426 bypassed and used to read arbitrary files. This was fixed by
427 enabling TeX configuration options that disallow unsafe TeX commands.
428 The fix was released on 30 Aug 2009 in version 3.1415926, and was
429 backported to stable in version 2.53.4. If you use the teximg plugin,
430 I recommend upgrading. ([[!cve CVE-2009-2944]])
432 ## javascript insertion via svg uris
434 Ivan Shmakov pointed out that the htmlscrubber allowed `data:image/*` urls,
435 including `data:image/svg+xml`. But svg can contain javascript, so that is
438 This hole was discovered on 12 March 2010 and fixed the same day
439 with the release of ikiwiki 3.20100312.
440 A fix was also backported to Debian etch, as version 2.53.5. I recommend
441 upgrading to one of these versions if your wiki can be edited by third
444 ## javascript insertation via insufficient htmlscrubbing of comments
446 Kevin Riggle noticed that it was not possible to configure
447 `htmlscrubber_skip` to scrub comments while leaving unscubbed the text
448 of eg, blog posts. Confusingly, setting it to "* and !comment(*)" did not
451 Additionally, it was discovered that comments' html was never scrubbed during
452 preview or moderation of comments with such a configuration.
454 These problems were discovered on 12 November 2010 and fixed the same
455 hour with the release of ikiwiki 3.20101112. ([[!cve CVE-2010-1673]])
457 ## javascript insertation via insufficient checking in comments
459 Dave B noticed that attempting to comment on an illegal page name could be
460 used for an XSS attack.
462 This hole was discovered on 22 Jan 2011 and fixed the same day with
463 the release of ikiwiki 3.20110122. An upgrade is recommended for sites
464 with the comments plugin enabled. ([[!cve CVE-2011-0428]])