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 svn commit access can forge "web commit from foo" and make it
18 appear on [[RecentChanges]] like foo committed. One way to avoid this would
19 be to limit web commits to those done by a certian user.
21 It's actually possible to force a whole series of svn commits to appear to
22 have come just before yours, by forging svn log output. This could be
23 guarded against by using svn log --xml.
25 ikiwiki escapes any html in svn commit logs to prevent other mischief.
33 ## image file etc attacks
35 If it enounters a file type it does not understand, ikiwiki just copies it
36 into place. So if you let users add any kind of file they like, they can
37 upload images, movies, windows executables, css files, etc (though not html
38 files). If these files exploit security holes in the browser of someone
39 who's viewing the wiki, that can be a security problem.
41 Of course nobody else seems to worry about this in other wikis, so should we?
43 Currently only people with direct svn commit access can upload such files
44 (and if you wanted to you could block that with a svn pre-commit hook).
45 Wsers with only web commit access are limited to editing pages as ikiwiki
46 doesn't support file uploads from browsers (yet), so they can't exploit
49 ## multiple accessors of wiki directory
51 If multiple people can write to the source directory ikiwiki is using, or
52 to the destination directory it writes files to, then one can cause trouble
53 for the other when they run ikiwiki through symlink attacks.
55 So it's best if only one person can ever write to those directories.
59 Setup files are not safe to keep in subversion with the rest of the wiki.
60 Just don't do it. [[ikiwiki.setup]] is *not* used as the setup file for
63 ## page locking can be bypassed via direct svn commits
65 A [[lock]]ed page can only be edited on the web by an admin, but
66 anyone who is allowed to commit direct to svn can bypass this. This is by
67 design, although a subversion pre-commit hook could be used to prevent
68 editing of locked pages when using subversion, if you really need to.
72 If your web server does any parsing of special sorts of files (for example,
73 server parsed html files), then if you let anyone else add files to the wiki,
74 they can try to use this to exploit your web server.
80 _(AKA, the assumptions that will be the root of most security holes...)_
82 ## exploting ikiwiki with bad content
84 Someone could add bad content to the wiki and hope to exploit ikiwiki.
85 Note that ikiwiki runs with perl taint checks on, so this is unlikely.
87 ## publishing cgi scripts
89 ikiwiki does not allow cgi scripts to be published as part of the wiki. Or
90 rather, the script is published, but it's not marked executable (except in
91 the case of "destination directory file replacement" below), so hopefully
92 your web server will not run it.
96 ikiwiki --wrapper is intended to generate a wrapper program that
97 runs ikiwiki to update a given wiki. The wrapper can in turn be made suid,
98 for example to be used in a [[post-commit]] hook by people who cannot write
99 to the html pages, etc.
101 If the wrapper script is made suid, then any bugs in this wrapper would be
102 security holes. The wrapper is written as securely as I know how, is based
103 on code that has a history of security use long before ikiwiki, and there's
108 ikiwiki does not expose untrusted data to the shell. In fact it doesn't use
109 system() at all, and the only use of backticks is on data supplied by the
110 wiki admin and untainted filenames. And it runs with taint checks on of
115 When ikiwiki runs as a cgi to edit a page, it is passed the name of the
116 page to edit. It has to make sure to sanitise this page, to prevent eg,
117 editing of ../../../foo, or editing of files that are not part of the wiki,
118 such as subversion dotfiles. This is done by sanitising the filename
119 removing unallowed characters, then making sure it doesn't start with "/"
120 or contain ".." or "/.svn/". Annoyingly ad-hoc, this kind of code is where
121 security holes breed. It needs a test suite at the very least.
123 ## CGI::Session security
125 I've audited this module and it is massively insecure by default. ikiwiki
126 uses it in one of the few secure ways; by forcing it to write to a
127 directory it controls (and not /tmp) and by setting a umask that makes the
128 file not be world readable.
130 ## cgi password security
132 Login to the wiki involves sending a password in cleartext over the net.
133 Cracking the password only allows editing the wiki as that user though.
134 If you care, you can use https, I suppose.
136 ## XSS holes in CGI output
138 ikiwiki has not yet been audited to ensure that all cgi script input/output
139 is sanitised to prevent XSS attacks. For example, a user can't register
140 with a username containing html code (anymore).
142 It's difficult to know for sure if all such avenues have really been
149 _(Unless otherwise noted, these were discovered and immediatey fixed by the
150 ikiwiki developers.)_
152 ## destination directory file replacement
154 Any file in the destination directory that is a valid page filename can be
155 replaced, even if it was not originally rendered from a page. For example,
156 ikiwiki.cgi could be edited in the wiki, and it would write out a
157 replacement. File permission is preseved. Yipes!
159 This was fixed by making ikiwiki check if the file it's writing to exists;
160 if it does then it has to be a file that it's aware of creating before, or
161 it will refuse to create it.
163 Still, this sort of attack is something to keep in mind.
167 Could a committer trick ikiwiki into following a symlink and operating on
168 some other tree that it shouldn't? svn supports symlinks, so one can get
169 into the repo. ikiwiki uses File::Find to traverse the repo, and does not
170 tell it to follow symlinks, but it might be possible to race replacing a
171 directory with a symlink and trick it into following the link.
173 Also, if someone checks in a symlink to /etc/passwd, ikiwiki would read and
174 publish that, which could be used to expose files a committer otherwise
177 To avoid this, ikiwiki will skip over symlinks when scanning for pages, and
178 uses locking to prevent more than one instance running at a time. The lock
179 prevents one ikiwiki from running a svn up at the wrong time to race
180 another ikiwiki. So only attackers who can write to the working copy on
181 their own can race it.
183 ## symlink + cgi attacks
185 Similarly, a svn commit of a symlink could be made, ikiwiki ignores it
186 because of the above, but the symlink is still there, and then you edit the
187 page from the web, which follows the symlink when reading the page, and
188 again when saving the changed page.
190 This was fixed by making ikiwiki refuse to read or write to files that are
191 symlinks, or that are in subdirectories that are symlinks, combined with
194 ## underlaydir override attacks
196 ikiwiki also scans an underlaydir for pages, this is used to provide stock
197 pages to all wikis w/o needing to copy them into the wiki. Since ikiwiki
198 internally stores only the base filename from the underlaydir or srcdir,
199 and searches for a file in either directory when reading a page source,
200 there is the potential for ikiwiki's scanner to reject a file from the
201 srcdir for some reason (such as it being a symlink), find a valid copy of
202 the file in the underlaydir, and then when loading the file, mistekenly
203 load the bad file from the srcdir.
205 This attack is avoided by making ikiwiki scan the srcdir first, and refuse
206 to add any files from the underlaydir if a file also exists in the srcdir
207 with the same name. **But**, note that this assumes that any given page can
208 be produced from a file with only one name (`page.mdwn` => `page.html`).
210 If it's possible for files with different names to produce a given page, it
211 would still be possible to use this attack to confuse ikiwiki into
212 rendering the wrong thing. This is not currently possible, but must be kept
213 in mind in the future when for example adding support for generating html
214 pages from source with some other extension.
216 ## XSS attacks in page content
218 ikiwiki supports [[HtmlSanitization]], though it can be turned off.