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 svn commit access can upload such files
45 (and if you wanted to you could block that with a svn 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 ## multiple accessors of wiki directory
52 If multiple people can write to the source directory ikiwiki is using, or
53 to the destination directory it writes files to, then one can cause trouble
54 for the other when they run ikiwiki through symlink attacks.
56 So it's best if only one person can ever write to those directories.
60 Setup files are not safe to keep in subversion with the rest of the wiki.
61 Just don't do it. [[ikiwiki.setup]] is *not* used as the setup file for
64 ## page locking can be bypassed via direct svn commits
66 A locked page can only be edited on the web by an admin, but
67 anyone who is allowed to commit direct to svn can bypass this. This is by
68 design, although a subversion pre-commit hook could be used to prevent
69 editing of locked pages when using subversion, if you really need to.
73 If your web server does any parsing of special sorts of files (for example,
74 server parsed html files), then if you let anyone else add files to the wiki,
75 they can try to use this to exploit your web server.
81 _(AKA, the assumptions that will be the root of most security holes...)_
83 ## exploiting ikiwiki with bad content
85 Someone could add bad content to the wiki and hope to exploit ikiwiki.
86 Note that ikiwiki runs with perl taint checks on, so this is unlikely.
88 One fun thing in ikiwiki is its handling of a PageSpec, which involves
89 translating it into perl and running the perl. Of course, this is done
90 *very* carefully to guard against injecting arbitrary perl code.
92 ## publishing cgi scripts
94 ikiwiki does not allow cgi scripts to be published as part of the wiki. Or
95 rather, the script is published, but it's not marked executable (except in
96 the case of "destination directory file replacement" below), so hopefully
97 your web server will not run it.
101 ikiwiki --wrapper is intended to generate a wrapper program that
102 runs ikiwiki to update a given wiki. The wrapper can in turn be made suid,
103 for example to be used in a [[post-commit]] hook by people who cannot write
104 to the html pages, etc.
106 If the wrapper script is made suid, then any bugs in this wrapper would be
107 security holes. The wrapper is written as securely as I know how, is based
108 on code that has a history of security use long before ikiwiki, and there's
113 ikiwiki does not expose untrusted data to the shell. In fact it doesn't use
114 system() at all, and the only use of backticks is on data supplied by the
115 wiki admin and untainted filenames. And it runs with taint checks on of
120 When ikiwiki runs as a cgi to edit a page, it is passed the name of the
121 page to edit. It has to make sure to sanitise this page, to prevent eg,
122 editing of ../../../foo, or editing of files that are not part of the wiki,
123 such as subversion dotfiles. This is done by sanitising the filename
124 removing unallowed characters, then making sure it doesn't start with "/"
125 or contain ".." or "/.svn/". Annoyingly ad-hoc, this kind of code is where
126 security holes breed. It needs a test suite at the very least.
128 ## CGI::Session security
130 I've audited this module and it is massively insecure by default. ikiwiki
131 uses it in one of the few secure ways; by forcing it to write to a
132 directory it controls (and not /tmp) and by setting a umask that makes the
133 file not be world readable.
135 ## cgi password security
137 Login to the wiki involves sending a password in cleartext over the net.
138 Cracking the password only allows editing the wiki as that user though.
139 If you care, you can use https, I suppose. If you do use https either for
140 all of the wiki, or just the cgi access, then consider using the sslcookie
143 ## XSS holes in CGI output
145 ikiwiki has not yet been audited to ensure that all cgi script input/output
146 is sanitised to prevent XSS attacks. For example, a user can't register
147 with a username containing html code (anymore).
149 It's difficult to know for sure if all such avenues have really been
152 ## HTML::Template security
154 If the [[plugins/template]] plugin is enabled, users can modify templates
155 like any other part of the wiki. This assumes that HTML::Template is secure
156 when used with untrusted/malicious templates. (Note that includes are not
157 allowed, so that's not a problem.)
163 The security of [[plugins]] depends on how well they're written and what
164 external tools they use. The plugins included in ikiwiki are all held to
165 the same standards as the rest of ikiwiki, but with that said, here are
166 some security notes for them.
168 * The [[plugins/img]] plugin assumes that imagemagick/perlmagick are secure
169 from malformed image attacks. Imagemagick has had security holes in the
170 past. To be able to exploit such a hole, a user would need to be able to
171 upload images to the wiki.
177 _(Unless otherwise noted, these were discovered and immediately fixed by the
178 ikiwiki developers.)_
180 ## destination directory file replacement
182 Any file in the destination directory that is a valid page filename can be
183 replaced, even if it was not originally rendered from a page. For example,
184 ikiwiki.cgi could be edited in the wiki, and it would write out a
185 replacement. File permission is preseved. Yipes!
187 This was fixed by making ikiwiki check if the file it's writing to exists;
188 if it does then it has to be a file that it's aware of creating before, or
189 it will refuse to create it.
191 Still, this sort of attack is something to keep in mind.
195 Could a committer trick ikiwiki into following a symlink and operating on
196 some other tree that it shouldn't? svn supports symlinks, so one can get
197 into the repo. ikiwiki uses File::Find to traverse the repo, and does not
198 tell it to follow symlinks, but it might be possible to race replacing a
199 directory with a symlink and trick it into following the link.
201 Also, if someone checks in a symlink to /etc/passwd, ikiwiki would read and
202 publish that, which could be used to expose files a committer otherwise
205 To avoid this, ikiwiki will skip over symlinks when scanning for pages, and
206 uses locking to prevent more than one instance running at a time. The lock
207 prevents one ikiwiki from running a svn up at the wrong time to race
208 another ikiwiki. So only attackers who can write to the working copy on
209 their own can race it.
211 ## symlink + cgi attacks
213 Similarly, a svn commit of a symlink could be made, ikiwiki ignores it
214 because of the above, but the symlink is still there, and then you edit the
215 page from the web, which follows the symlink when reading the page
216 (exposing the content), and again when saving the changed page (changing
219 This was fixed for page saving by making ikiwiki refuse to write to files
220 that are symlinks, or that are in subdirectories that are symlinks,
221 combined with the above locking.
223 For page editing, it's fixed by ikiwiki checking to make sure that it
224 already has found a page by scanning the tree, before loading it for
225 editing, which as described above, also is done in a way that avoids
228 ## underlaydir override attacks
230 ikiwiki also scans an underlaydir for pages, this is used to provide stock
231 pages to all wikis w/o needing to copy them into the wiki. Since ikiwiki
232 internally stores only the base filename from the underlaydir or srcdir,
233 and searches for a file in either directory when reading a page source,
234 there is the potential for ikiwiki's scanner to reject a file from the
235 srcdir for some reason (such as it being contained in a directory that is
236 symlinked in), find a valid copy of the file in the underlaydir, and then
237 when loading the file, mistakenly load the bad file from the srcdir.
239 This attack is avoided by making ikiwiki refuse to add any files from the
240 underlaydir if a file also exists in the srcdir with the same name.
242 ## multiple page source issues
244 Note that I previously worried that underlay override attacks could also be
245 accomplished if ikiwiki were extended to support other page markup
246 languages besides markdown. However, a closer look indicates that this is
247 not a problem: ikiwiki does preserve the file extension when storing the
248 source filename of a page, so a file with another extension that renders to
249 the same page name can't bypass the check. Ie, ikiwiki won't skip foo.rst
250 in the srcdir, find foo.mdwn in the underlay, decide to render page foo and
251 then read the bad foo.mdwn. Instead it will remember the .rst extension and
252 only render a file with that extension.
254 ## XSS attacks in page content
256 ikiwiki supports protecting users from their own broken browsers via the
257 [[plugins/htmlscrubber]] plugin, which is enabled by default.
261 It's was possible to force a whole series of svn commits to appear to
262 have come just before yours, by forging svn log output. This was
263 guarded against by using svn log --xml.
265 ikiwiki escapes any html in svn commit logs to prevent other mischief.
269 XML::Parser is used by the aggregation plugin, and has some security holes.
270 Bug #[378411](http://bugs.debian.org/378411) does not
271 seem to affect our use, since the data is not encoded as utf-8 at that
272 point. #[378412](http://bugs.debian.org/378412) could affect us, although it
273 doesn't seem very exploitable. It has a simple fix, and has been fixed in
278 Various directives that cause one page to be included into another could
279 be exploited to DOS the wiki, by causing a loop. Ikiwiki has always guarded
280 against this one way or another; the current solution should detect all
281 types of loops involving preprocessor directives.
283 ## Online editing of existing css and images
285 A bug in ikiwiki allowed the web-based editor to edit any file that was in
286 the wiki, not just files that are page sources. So an attacker (or a
287 genuinely helpful user, which is how the hole came to light) could edit
288 files like style.css. It is also theoretically possible that an attacker
289 could have used this hole to edit images or other files in the wiki, with
290 some difficulty, since all editing would happen in a textarea.
292 This hole was discovered on 10 Feb 2007 and fixed the same day with the
293 release of ikiwiki 1.42. A fix was also backported to Debian etch, as
294 version 1.33.1. I recommend upgrading to one of these versions if your wiki
297 ## html insertion via title
299 Missing html escaping of the title contents allowed a web-based editor to
300 insert arbitrary html inside the title tag of a page. Since that part of
301 the page is not processed by the htmlscrubber, evil html could be injected.
303 This hole was discovered on 21 March 2007 and fixed the same day (er, hour)
304 with the release of ikiwiki 1.46. A fix was also backported to Debian etch,
305 as version 1.33.2. I recommend upgrading to one of these versions if your
306 wiki allows web editing or aggregates feeds.
308 ## javascript insertion via meta tags
310 It was possible to use the meta plugin's meta tags to insert arbitrary
311 url contents, which could be used to insert stylesheet information
312 containing javascript. This was fixed by sanitising meta tags.
314 This hole was discovered on 21 March 2007 and fixed the same day
315 with the release of ikiwiki 1.47. A fix was also backported to Debian etch,
316 as version 1.33.3. I recommend upgrading to one of these versions if your
317 wiki can be edited by third parties.