165 lines
6.8 KiB
Markdown
165 lines
6.8 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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# Probable holes
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## html attacks
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ikiwiki does not attempt to do any santization of the html on the wiki.
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[[MarkDown]] allows embedding of arbitrary html into a markdown document. If
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you let anyone else edit files on the wiki, then anyone can have fun exploiting
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the web browser bug of the day. This type of attack is typically referred
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to as an XSS attack ([google](http://www.google.com/search?q=xss+attack)).
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## image files 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. If these files exploit security holes in the browser of someone 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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## 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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## multiple accessors of wiki directory
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If multiple people can write to the source directory ikiwiki is using, or to the destination directory it writes files to, then one can cause trouble 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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## svn commit logs
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Anyone with svn commit access can forge "web commit from foo" and make it appear on [[RecentChanges]] like foo committed. One way to avoid this would 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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## 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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----
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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 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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# Fixed holes
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_(Unless otherwise noted, these were discovered and immediatey fixed by the 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, combined with the above locking.
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