219 lines
8.5 KiB
Markdown
219 lines
8.5 KiB
Markdown
Let's do an ikiwiki security analysis..
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If you are using ikiwiki to render pages that only you can edit, do not
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generate any wrappers, and do not use the cgi, then there are no more
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security issues with this program than with cat(1). If, however, you let
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others edit pages in your wiki, then some possible security issues do need
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to be kept in mind.
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----
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# Probable holes
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_(The list of things to fix.)_
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## svn commit logs
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Anyone with svn commit access can forge "web commit from foo" and make it
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appear on [[RecentChanges]] like foo committed. One way to avoid this would
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be to limit web commits to those done by a certian user.
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It's actually possible to force a whole series of svn commits to appear to
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have come just before yours, by forging svn log output. This could be
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guarded against by using svn log --xml.
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ikiwiki escapes any html in svn commit logs to prevent other mischief.
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----
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# Potential gotchas
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_(Things not to do.)_
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## image file etc attacks
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If it enounters a file type it does not understand, ikiwiki just copies it
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into place. So if you let users add any kind of file they like, they can
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upload images, movies, windows executables, css files, etc (though not html
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files). If these files exploit security holes in the browser of someone
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who's viewing the wiki, that can be a security problem.
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Of course nobody else seems to worry about this in other wikis, so should we?
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Currently only people with direct svn commit access can upload such files
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(and if you wanted to you could block that with a svn pre-commit hook).
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Wsers with only web commit access are limited to editing pages as ikiwiki
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doesn't support file uploads from browsers (yet), so they can't exploit
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this.
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## multiple accessors of wiki directory
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If multiple people can write to the source directory ikiwiki is using, or
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to the destination directory it writes files to, then one can cause trouble
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for the other when they run ikiwiki through symlink attacks.
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So it's best if only one person can ever write to those directories.
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## setup files
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Setup files are not safe to keep in subversion with the rest of the wiki.
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Just don't do it. [[ikiwiki.setup]] is *not* used as the setup file for
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this wiki, BTW.
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## page locking can be bypassed via direct svn commits
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A [[lock]]ed page can only be edited on the web by an admin, but
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anyone who is allowed to commit direct to svn can bypass this. This is by
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design, although a subversion pre-commit hook could be used to prevent
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editing of locked pages when using subversion, if you really need to.
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## web server attacks
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If your web server does any parsing of special sorts of files (for example,
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server parsed html files), then if you let anyone else add files to the wiki,
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they can try to use this to exploit your web server.
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----
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# Hopefully non-holes
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_(AKA, the assumptions that will be the root of most security holes...)_
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## exploting ikiwiki with bad content
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Someone could add bad content to the wiki and hope to exploit ikiwiki.
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Note that ikiwiki runs with perl taint checks on, so this is unlikely.
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## publishing cgi scripts
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ikiwiki does not allow cgi scripts to be published as part of the wiki. Or
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rather, the script is published, but it's not marked executable (except in
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the case of "destination directory file replacement" below), so hopefully
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your web server will not run it.
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## suid wrappers
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ikiwiki --wrapper is intended to generate a wrapper program that
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runs ikiwiki to update a given wiki. The wrapper can in turn be made suid,
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for example to be used in a [[post-commit]] hook by people who cannot write
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to the html pages, etc.
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If the wrapper script is made suid, then any bugs in this wrapper would be
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security holes. The wrapper is written as securely as I know how, is based
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on code that has a history of security use long before ikiwiki, and there's
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been no problem yet.
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## shell exploits
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ikiwiki does not expose untrusted data to the shell. In fact it doesn't use
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system() at all, and the only use of backticks is on data supplied by the
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wiki admin and untainted filenames. And it runs with taint checks on of
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course..
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## cgi data security
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When ikiwiki runs as a cgi to edit a page, it is passed the name of the
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page to edit. It has to make sure to sanitise this page, to prevent eg,
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editing of ../../../foo, or editing of files that are not part of the wiki,
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such as subversion dotfiles. This is done by sanitising the filename
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removing unallowed characters, then making sure it doesn't start with "/"
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or contain ".." or "/.svn/". Annoyingly ad-hoc, this kind of code is where
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security holes breed. It needs a test suite at the very least.
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## CGI::Session security
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I've audited this module and it is massively insecure by default. ikiwiki
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uses it in one of the few secure ways; by forcing it to write to a
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directory it controls (and not /tmp) and by setting a umask that makes the
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file not be world readable.
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## cgi password security
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Login to the wiki involves sending a password in cleartext over the net.
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Cracking the password only allows editing the wiki as that user though.
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If you care, you can use https, I suppose.
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## XSS holes in CGI output
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ikiwiki has not yet been audited to ensure that all cgi script input/output
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is sanitised to prevent XSS attacks. For example, a user can't register
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with a username containing html code (anymore).
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It's difficult to know for sure if all such avenues have really been
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closed though.
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----
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# Fixed holes
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_(Unless otherwise noted, these were discovered and immediatey fixed by the
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ikiwiki developers.)_
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## destination directory file replacement
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Any file in the destination directory that is a valid page filename can be
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replaced, even if it was not originally rendered from a page. For example,
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ikiwiki.cgi could be edited in the wiki, and it would write out a
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replacement. File permission is preseved. Yipes!
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This was fixed by making ikiwiki check if the file it's writing to exists;
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if it does then it has to be a file that it's aware of creating before, or
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it will refuse to create it.
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Still, this sort of attack is something to keep in mind.
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## symlink attacks
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Could a committer trick ikiwiki into following a symlink and operating on
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some other tree that it shouldn't? svn supports symlinks, so one can get
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into the repo. ikiwiki uses File::Find to traverse the repo, and does not
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tell it to follow symlinks, but it might be possible to race replacing a
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directory with a symlink and trick it into following the link.
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Also, if someone checks in a symlink to /etc/passwd, ikiwiki would read and
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publish that, which could be used to expose files a committer otherwise
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wouldn't see.
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To avoid this, ikiwiki will skip over symlinks when scanning for pages, and
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uses locking to prevent more than one instance running at a time. The lock
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prevents one ikiwiki from running a svn up at the wrong time to race
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another ikiwiki. So only attackers who can write to the working copy on
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their own can race it.
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## symlink + cgi attacks
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Similarly, a svn commit of a symlink could be made, ikiwiki ignores it
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because of the above, but the symlink is still there, and then you edit the
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page from the web, which follows the symlink when reading the page, and
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again when saving the changed page.
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This was fixed by making ikiwiki refuse to read or write to files that are
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symlinks, or that are in subdirectories that are symlinks, combined with
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the above locking.
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## underlaydir override attacks
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ikiwiki also scans an underlaydir for pages, this is used to provide stock
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pages to all wikis w/o needing to copy them into the wiki. Since ikiwiki
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internally stores only the base filename from the underlaydir or srcdir,
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and searches for a file in either directory when reading a page source,
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there is the potential for ikiwiki's scanner to reject a file from the
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srcdir for some reason (such as it being a symlink), find a valid copy of
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the file in the underlaydir, and then when loading the file, mistekenly
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load the bad file from the srcdir.
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This attack is avoided by making ikiwiki scan the srcdir first, and refuse
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to add any files from the underlaydir if a file also exists in the srcdir
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with the same name. **But**, note that this assumes that any given page can
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be produced from a file with only one name (`page.mdwn` => `page.html`).
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If it's possible for files with different names to produce a given page, it
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would still be possible to use this attack to confuse ikiwiki into
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rendering the wrong thing. This is not currently possible, but must be kept
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in mind in the future when for example adding support for generating html
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pages from source with some other extension.
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## XSS attacks in page content
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ikiwiki supports [[HtmlSanitization]], though it can be turned off.
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