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
13 _(The list of things to fix.)_
17 Anyone with direct commit access can forge "web commit from foo" and
18 make it appear on [[RecentChanges]] like foo committed. One way to avoid
19 this would be to limit web commits to those done by a certian user.
21 ## other stuff to look at
23 I need to audit the git backend a bit, and have been meaning to
24 see if any CRLF injection type things can be done in the CGI code.
32 ## image file etc attacks
34 If it enounters a file type it does not understand, ikiwiki just copies it
35 into place. So if you let users add any kind of file they like, they can
36 upload images, movies, windows executables, css files, etc (though not html
37 files). If these files exploit security holes in the browser of someone
38 who's viewing the wiki, that can be a security problem.
40 Of course nobody else seems to worry about this in other wikis, so should we?
42 Currently only people with direct svn commit access can upload such files
43 (and if you wanted to you could block that with a svn pre-commit hook).
44 Users with only web commit access are limited to editing pages as ikiwiki
45 doesn't support file uploads from browsers (yet), so they can't exploit
48 ## multiple accessors of wiki directory
50 If multiple people can write to the source directory ikiwiki is using, or
51 to the destination directory it writes files to, then one can cause trouble
52 for the other when they run ikiwiki through symlink attacks.
54 So it's best if only one person can ever write to those directories.
58 Setup files are not safe to keep in subversion with the rest of the wiki.
59 Just don't do it. [[ikiwiki.setup]] is *not* used as the setup file for
62 ## page locking can be bypassed via direct svn commits
64 A locked page can only be edited on the web by an admin, but
65 anyone who is allowed to commit direct to svn can bypass this. This is by
66 design, although a subversion pre-commit hook could be used to prevent
67 editing of locked pages when using subversion, if you really need to.
71 If your web server does any parsing of special sorts of files (for example,
72 server parsed html files), then if you let anyone else add files to the wiki,
73 they can try to use this to exploit your web server.
79 _(AKA, the assumptions that will be the root of most security holes...)_
81 ## exploting ikiwiki with bad content
83 Someone could add bad content to the wiki and hope to exploit ikiwiki.
84 Note that ikiwiki runs with perl taint checks on, so this is unlikely.
86 ## publishing cgi scripts
88 ikiwiki does not allow cgi scripts to be published as part of the wiki. Or
89 rather, the script is published, but it's not marked executable (except in
90 the case of "destination directory file replacement" below), so hopefully
91 your web server will not run it.
95 ikiwiki --wrapper is intended to generate a wrapper program that
96 runs ikiwiki to update a given wiki. The wrapper can in turn be made suid,
97 for example to be used in a [[post-commit]] hook by people who cannot write
98 to the html pages, etc.
100 If the wrapper script is made suid, then any bugs in this wrapper would be
101 security holes. The wrapper is written as securely as I know how, is based
102 on code that has a history of security use long before ikiwiki, and there's
107 ikiwiki does not expose untrusted data to the shell. In fact it doesn't use
108 system() at all, and the only use of backticks is on data supplied by the
109 wiki admin and untainted filenames. And it runs with taint checks on of
114 When ikiwiki runs as a cgi to edit a page, it is passed the name of the
115 page to edit. It has to make sure to sanitise this page, to prevent eg,
116 editing of ../../../foo, or editing of files that are not part of the wiki,
117 such as subversion dotfiles. This is done by sanitising the filename
118 removing unallowed characters, then making sure it doesn't start with "/"
119 or contain ".." or "/.svn/". Annoyingly ad-hoc, this kind of code is where
120 security holes breed. It needs a test suite at the very least.
122 ## CGI::Session security
124 I've audited this module and it is massively insecure by default. ikiwiki
125 uses it in one of the few secure ways; by forcing it to write to a
126 directory it controls (and not /tmp) and by setting a umask that makes the
127 file not be world readable.
129 ## cgi password security
131 Login to the wiki involves sending a password in cleartext over the net.
132 Cracking the password only allows editing the wiki as that user though.
133 If you care, you can use https, I suppose.
135 ## XSS holes in CGI output
137 ikiwiki has not yet been audited to ensure that all cgi script input/output
138 is sanitised to prevent XSS attacks. For example, a user can't register
139 with a username containing html code (anymore).
141 It's difficult to know for sure if all such avenues have really been
148 _(Unless otherwise noted, these were discovered and immediately fixed by the
149 ikiwiki developers.)_
151 ## destination directory file replacement
153 Any file in the destination directory that is a valid page filename can be
154 replaced, even if it was not originally rendered from a page. For example,
155 ikiwiki.cgi could be edited in the wiki, and it would write out a
156 replacement. File permission is preseved. Yipes!
158 This was fixed by making ikiwiki check if the file it's writing to exists;
159 if it does then it has to be a file that it's aware of creating before, or
160 it will refuse to create it.
162 Still, this sort of attack is something to keep in mind.
166 Could a committer trick ikiwiki into following a symlink and operating on
167 some other tree that it shouldn't? svn supports symlinks, so one can get
168 into the repo. ikiwiki uses File::Find to traverse the repo, and does not
169 tell it to follow symlinks, but it might be possible to race replacing a
170 directory with a symlink and trick it into following the link.
172 Also, if someone checks in a symlink to /etc/passwd, ikiwiki would read and
173 publish that, which could be used to expose files a committer otherwise
176 To avoid this, ikiwiki will skip over symlinks when scanning for pages, and
177 uses locking to prevent more than one instance running at a time. The lock
178 prevents one ikiwiki from running a svn up at the wrong time to race
179 another ikiwiki. So only attackers who can write to the working copy on
180 their own can race it.
182 ## symlink + cgi attacks
184 Similarly, a svn commit of a symlink could be made, ikiwiki ignores it
185 because of the above, but the symlink is still there, and then you edit the
186 page from the web, which follows the symlink when reading the page
187 (exposing the content), and again when saving the changed page (changing
190 This was fixed for page saving by making ikiwiki refuse to write to files
191 that are symlinks, or that are in subdirectories that are symlinks,
192 combined with the above locking.
194 For page editing, it's fixed by ikiwiki checking to make sure that it
195 already has found a page by scanning the tree, before loading it for
196 editing, which as described above, also is done in a way that avoids
199 ## underlaydir override attacks
201 ikiwiki also scans an underlaydir for pages, this is used to provide stock
202 pages to all wikis w/o needing to copy them into the wiki. Since ikiwiki
203 internally stores only the base filename from the underlaydir or srcdir,
204 and searches for a file in either directory when reading a page source,
205 there is the potential for ikiwiki's scanner to reject a file from the
206 srcdir for some reason (such as it being contained in a directory that is
207 symlinked in), find a valid copy of the file in the underlaydir, and then
208 when loading the file, mistakenly load the bad file from the srcdir.
210 This attack is avoided by making ikiwiki refuse to add any files from the
211 underlaydir if a file also exists in the srcdir with the same name.
213 ## multiple page source issues
215 Note that I previously worried that underlay override attacks could also be
216 accomplished if ikiwiki were extended to support other page markup
217 languages besides markdown. However, a closer look indicates that this is
218 not a problem: ikiwiki does preserve the file extension when storing the
219 source filename of a page, so a file with another extension that renders to
220 the same page name can't bypass the check. Ie, ikiwiki won't skip foo.rst
221 in the srcdir, find foo.mdwn in the underlay, decide to render page foo and
222 then read the bad foo.mdwn. Instead it will remember the .rst extension and
223 only render a file with that extension.
225 ## XSS attacks in page content
227 ikiwiki supports protecting users from their own broken browsers via the
228 [[plugins/htmlscrubber]] plugin, which is enabled by default.
232 It's was possible to force a whole series of svn commits to appear to
233 have come just before yours, by forging svn log output. This was
234 guarded against by using svn log --xml.
236 ikiwiki escapes any html in svn commit logs to prevent other mischief.