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