Drupal CKEditor 3.0 - 3.6.2 - Persistent EventHandler XSS

[InterN0T Advisories <advisories@xxxxxxxxxxxx>]

# Exploit Title: Drupal CKEditor 3.0 - 3.6.2 - Persistent EventHandler XSS
# Google Dork: "inurl:"sites/all/modules/ckeditor" -drupalcode.org" 
# Google Results: Approximately 379.000 results
# Date: 18th January 2012
# Author: MaXe @InterN0T (Found in a private Hatforce.com Penetration
Test)
# Software Link: http://ckeditor.com/ & http://drupal.org/node/1332022
# Version: 3.0 - Current 3.6.2 (Drupal module: 6.x-1.8)
# Screenshot: http://i.imgur.com/8TP6w.png
# Tested on: Windows + FireFox 8.0 & Internet Explorer 8.0

 
 Drupal CKEditor - Persistent / Stored Cross-Site Scripting
 
 
Versions Affected: 3.0 - 3.6.2 (Developers confirm all versions since 3.0
are affected.)
 
Info:
CKEditor is a text editor to be used inside web pages. It's a WYSIWYG
editor, which
means that the text being edited on it looks as similar as possible to the
results users
have when publishing it. It brings to the web common editing features
found on desktop
editing applications like Microsoft Word and OpenOffice.
 
External Links:
http://ckeditor.com/
http://drupal.org/node/1332022
 
Credits: MaXe (@InterN0T) - Hatforce.com
 
 
-:: The Advisory ::-
CKEditor is prone to Persistent Cross-Site Scripting within the actual
editor, as
it is possible for an attacker could maliciously inject eventhandlers
serving java-
script code in preview / editing in html mode.

If an attacker injects an eventhandler into an image, such as
"onload='alert(0);'",
then the javascript will execute, even if the data is saved and previewed
in editing
mode later on. (The XSS will only executing during preview / editing in
html mode.)

If an administrator tries to edit the comment afterward, or is logged in
and browses
to the edit page of the malicious comment, then he or she will execute the
javascript, 
allowing attacker controlled code to run in the context of the browser.

 
Proof of Concept:
Switching to "raw mode" in CKEditor and then writing: 
<p><img onload="alert(0);"
src="http://1.images.napster.com/mp3s/2348/resources/324/363/files/324363272.jpg";
/></p>

Will become this when it is saved: 
<p><img data-cke-pa-onload="alert(0);"
src="http://1.images.napster.com/mp3s/2348/resources/324/363/files/324363272.jpg";
data-cke-saved-src="http://1.images.napster.com/mp3s/2348/resources/324/363/files/324363272.jpg";></p>

If one searches for alert(0); in Firebug after the code has been injected
and executed, the location of the script will be:
$full_url_to_script/event/seq/4/onload
Where $full_url_to_script is e.g. the following:
http://localhost/drupal/drupal-6.22/?q=comment/edit/3/event/seq/4/onload

The content of this script is:
function onload(event) {
alert(0);
}

As there is a HTML filter in Drupal, it does not matter whether the <img>
tag is allowed in this case, as it was possible to execute the eventhandler
either way. (And even store the data.)


-:: Solution ::-
There is currently no solution, as it's not a critical bug according to
developers. See comments at: https://dev.ckeditor.com/ticket/8630 for more
information.
At the same page there is an unofficial patch that should fix the problem,
however it seems that it will not fix the bug in Chrome.
 
 
Disclosure Information:
6th December 2011 - Vulnerability found during a private
http://www.hatforce.com Penetration Test
7th December 2011 - Researched and confirmed the vulnerability
4th January 2012 - Reported to Drupal and CKEditor via
http://drupal.org/project/ckeditor and http://dev.ckeditor.com/ and
http://cksource.com/contact
18th January 2012 - Developers of CKEditor has been contacted several
times, nothing has happened in two weeks and the advisory has been
available to the public via bugtrackers. Vulnerability released to the
general public.