web commit by http://joey.kitenet.net/: poll vote (No opinion)

[git.ikiwiki.info.git] / doc / security.mdwn

diff --git a/doc/security.mdwn b/doc/security.mdwn
index 0731ff3c5794cfe7b16f64286e1481c3d74ac836..c51cd5b953727c6aa900c483bf616b6e321e3687 100644 (file)
--- a/doc/security.mdwn
+++ b/doc/security.mdwn
@@ -1,4 +1,4 @@
-Let's do an ikiwiki security analysis..
+Let's do an ikiwiki security analysis.

 
 If you are using ikiwiki to render pages that only you can edit, do not
 generate any wrappers, and do not use the cgi, then there are no more
 
 If you are using ikiwiki to render pages that only you can edit, do not
 generate any wrappers, and do not use the cgi, then there are no more


@@ -6,61 +6,89 @@ security issues with this program than with cat(1). If, however, you let
 others edit pages in your wiki, then some possible security issues do need
 to be kept in mind.
 
 others edit pages in your wiki, then some possible security issues do need
 to be kept in mind.
 

+[[toc levels=2]]
+
+----
+

 # Probable holes
 
 # Probable holes
 

-## html attacks
+_(The list of things to fix.)_
+
+## commit spoofing

 
 

-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)).
+Anyone with direct 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 certain user.

 
 

-## image files etc attacks
+## other stuff to look at
+
+I need to audit the git backend a bit, and have been meaning to
+see if any CRLF injection type things can be done in the CGI code.
+
+----
+
+# Potential gotchas
+
+_(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
 
 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?
 
 
 Of course nobody else seems to worry about this in other wikis, so should we?
 

-## 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.
+Currently only people with direct commit access can upload such files
+(and if you wanted to you could block that with a pre-commit hook).
+Users 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
 
 
 ## 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.
+If multiple people can directly 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.
+So it's best if only one person can ever directly write to those directories.

 
 ## setup files
 
 
 ## 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.
+Setup files are not safe to keep in the same revision control repository
+with the rest of the wiki. Just don't do it. [[ikiwiki.setup]] is *not*
+used as the setup file for this wiki, BTW.

 
 

-## svn commit logs
+## page locking can be bypassed via direct commits

 
 

-Anyone with svn commit access can forge "web commit from foo" and make it appeat on [[RecentChanges]] like foo committed. One way to avoid this would be to limit web commits to those done by a certian user.
+A locked page can only be edited on the web by an admin, but anyone who is
+allowed to commit directly to the repository can bypass this. This is by
+design, although a pre-commit hook could be used to prevent editing of
+locked pages, if you really need to.

 
 

-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 somewhat by revision number scanning, since the forged revisions would duplicate the numbers of unforged ones. Or subversion could fix svn log to indent commit messages, which would make such forgery impossible..
+## web server attacks

 
 

-ikiwiki escapes any html in svn commit logs to prevent other mischief.
+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.

 
 ----
 
 # Hopefully non-holes
 
 
 ----
 
 # Hopefully non-holes
 

-(AKA, the assumptions that will be the root of most security holes...)
+_(AKA, the assumptions that will be the root of most security holes...)_

 
 

-## exploting ikiwiki with bad content
+## exploiting 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.
 
 
 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.
 

+One fun thing in ikiwiki is its handling of a PageSpec, which involves
+translating it into perl and running the perl. Of course, this is done
+*very* carefully to guard against injecting arbitrary perl code.
+

 ## publishing cgi scripts
 
 ikiwiki does not allow cgi scripts to be published as part of the wiki. Or
 ## publishing cgi scripts
 
 ikiwiki does not allow cgi scripts to be published as part of the wiki. Or


@@ -84,7 +112,8 @@ been no problem yet.
 
 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
 
 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..
+wiki admin and untainted filenames. And it runs with taint checks on of
+course..

 
 ## cgi data security
 
 
 ## cgi data security
 


@@ -93,8 +122,8 @@ page to edit. It has to make sure to sanitise this page, to prevent eg,
 editing of ../../../foo, or editing of files that are not part of the wiki,
 such as subversion dotfiles. This is done by sanitising the filename
 removing unallowed characters, then making sure it doesn't start with "/"
 editing of ../../../foo, or editing of files that are not part of the wiki,
 such as subversion dotfiles. This is done by sanitising the filename
 removing unallowed characters, then making sure it doesn't start with "/"

-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.
+or contain ".." or "/.svn/", etc. Annoyingly ad-hoc, this kind of code is
+where security holes breed. It needs a test suite at the very least.

 
 ## CGI::Session security
 
 
 ## CGI::Session security
 


@@ -107,9 +136,46 @@ file not be world readable.
 
 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.
 
 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.
+If you care, you can use https, I suppose. If you do use https either for
+all of the wiki, or just the cgi access, then consider using the sslcookie
+option.
+
+## XSS holes in CGI output
+
+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).
+
+It's difficult to know for sure if all such avenues have really been
+closed though.
+
+## HTML::Template security

 
 

-# Fixed holes.
+If the [[plugins/template]] plugin is enabled, users can modify templates
+like any other part of the wiki. This assumes that HTML::Template is secure
+when used with untrusted/malicious templates. (Note that includes are not
+allowed, so that's not a problem.)
+
+----
+
+# Plugins
+
+The security of [[plugins]] depends on how well they're written and what
+external tools they use. The plugins included in ikiwiki are all held to
+the same standards as the rest of ikiwiki, but with that said, here are
+some security notes for them.
+
+* The [[plugins/img]] plugin assumes that imagemagick/perlmagick are secure
+  from malformed image attacks. Imagemagick has had security holes in the
+  past. To be able to exploit such a hole, a user would need to be able to
+  upload images to the wiki.
+
+----
+
+# Fixed holes
+
+_(Unless otherwise noted, these were discovered and immediately fixed by the
+ikiwiki developers.)_

 
 ## destination directory file replacement
 
 
 ## destination directory file replacement
 


@@ -132,6 +198,150 @@ 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.
 
 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.
+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/git pull/etc 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 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
+(exposing the content), and again when saving the changed page (changing
+the content).
+
+This was fixed for page saving by making ikiwiki refuse to write to files
+that are symlinks, or that are in subdirectories that are symlinks,
+combined with the above locking.
+
+For page editing, it's fixed by ikiwiki checking to make sure that it
+already has found a page by scanning the tree, before loading it for
+editing, which as described above, also is done in a way that avoids
+symlink attacks.
+
+## 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 contained in a directory that is
+symlinked in), find a valid copy of the file in the underlaydir, and then
+when loading the file, mistakenly load the bad file from the srcdir.
+
+This attack is avoided by making ikiwiki refuse to add any files from the
+underlaydir if a file also exists in the srcdir with the same name.
+
+## multiple page source issues
+
+Note that I previously worried that underlay override attacks could also be
+accomplished if ikiwiki were extended to support other page markup
+languages besides markdown. However, a closer look indicates that this is
+not a problem: ikiwiki does preserve the file extension when storing the
+source filename of a page, so a file with another extension that renders to
+the same page name can't bypass the check. Ie, ikiwiki won't skip foo.rst
+in the srcdir, find foo.mdwn in the underlay, decide to render page foo and
+then read the bad foo.mdwn. Instead it will remember the .rst extension and
+only render a file with that extension.
+
+## XSS attacks in page content
+
+ikiwiki supports protecting users from their own broken browsers via the
+[[plugins/htmlscrubber]] plugin, which is enabled by default.
+
+## svn commit logs
+
+It's was possible to force a whole series of svn commits to appear to
+have come just before yours, by forging svn log output. This was
+guarded against by using svn log --xml.
+
+ikiwiki escapes any html in svn commit logs to prevent other mischief.

 
 

-To avoid this, ikiwiki will avoid reading files that are symlinks, 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.
\ No newline at end of file
+## XML::Parser
+
+XML::Parser is used by the aggregation plugin, and has some security holes. 
+Bug #[378411](http://bugs.debian.org/378411) does not
+seem to affect our use, since the data is not encoded as utf-8 at that
+point. #[378412](http://bugs.debian.org/378412) could affect us, although it
+doesn't seem very exploitable. It has a simple fix, and has been fixed in
+Debian unstable.
+
+## include loops
+
+Various directives that cause one page to be included into another could
+be exploited to DOS the wiki, by causing a loop. Ikiwiki has always guarded
+against this one way or another; the current solution should detect all
+types of loops involving preprocessor directives.
+
+## Online editing of existing css and images
+
+A bug in ikiwiki allowed the web-based editor to edit any file that was in
+the wiki, not just files that are page sources. So an attacker (or a
+genuinely helpful user, which is how the hole came to light) could edit
+files like style.css. It is also theoretically possible that an attacker
+could have used this hole to edit images or other files in the wiki, with
+some difficulty, since all editing would happen in a textarea.
+
+This hole was discovered on 10 Feb 2007 and fixed the same day with the
+release of ikiwiki 1.42. A fix was also backported to Debian etch, as
+version 1.33.1. I recommend upgrading to one of these versions if your wiki
+allows web editing.
+
+## html insertion via title
+
+Missing html escaping of the title contents allowed a web-based editor to
+insert arbitrary html inside the title tag of a page. Since that part of
+the page is not processed by the htmlscrubber, evil html could be injected.
+
+This hole was discovered on 21 March 2007 and fixed the same day (er, hour) 
+with the release of ikiwiki 1.46. A fix was also backported to Debian etch,
+as version 1.33.2. I recommend upgrading to one of these versions if your
+wiki allows web editing or aggregates feeds.
+
+## javascript insertion via meta tags
+
+It was possible to use the meta plugin's meta tags to insert arbitrary
+url contents, which could be used to insert stylesheet information
+containing javascript. This was fixed by sanitising meta tags.
+
+This hole was discovered on 21 March 2007 and fixed the same day
+with the release of ikiwiki 1.47. A fix was also backported to Debian etch,
+as version 1.33.3. I recommend upgrading to one of these versions if your
+wiki can be edited by third parties.
+
+## insufficient checking for symlinks in srcdir path
+
+Ikiwiki did not check if path to the srcdir to contained a symlink. If an
+attacker had commit access to the directories in the path, they could
+change it to a symlink, causing ikiwiki to read and publish files that were
+not intended to be published. (But not write to them due to other checks.)
+
+In most configurations, this is not exploitable, because the srcdir is
+checked out of revision control, but the directories leading up to it are
+not. Or, the srcdir is a single subdirectory of a project in revision
+control (ie, `ikiwiki/doc`), and if the subdirectory were a symlink,
+ikiwiki would still typically not follow it.
+
+There are at least two configurations where this is exploitable:
+
+* If the srcdir is a deeper subdirectory of a project. For example if it is
+  `project/foo/doc`, an an attacker can replace `foo` with a symlink to a
+  directory containing a `doc` directory (not a symlink), then ikiwiki
+  would follow the symlink.
+* If the path to the srcdir in ikiwiki's configuration ended in "/", 
+  and the srcdir is a single subdirectory of a project, (ie,
+  `ikiwiki/doc/`), the srcdir could be a symlink and ikiwiki would not
+  notice.
+
+This security hole was discovered on 26 November 2007 and fixed the same
+day with the release of ikiwiki 2.14. I recommend upgrading to this version
+if your wiki can be committed to by third parties. Alternatively, don't use
+a trailing slash in the srcdir, and avoid the (unusual) configurations that
+allow the security hole to be exploited.