Product: Wordpress-MU (multi-user)
Version: Versions prior to 2.6 are affected
Url: http://mu.wordpress.org
Affected by: Coss Site Scripting Attack


I. Introduction.

Wordpress-MU, or multi-user, allows to run unlimited blogs with a
single install of wordpress. It's widely used, some examples are
WordPress.com or universities like Harvard


II. Description and Impact

Wordpress-MU is affected by a Cross Site Scripting vulnerability, an
attacker can perform an XSS attack that allows him to access the
targeted user cookies to gain administrator privileges

In /wp-admin/wpmu-blogs.php an attacker can inject javascript code,
the input variables "s" and "ip_address" of GET method aren't properly
sanitized


Here is a poc:

The impact is the attacker can gain administrator privileges on the
application.


III. Timeline

May 14th, 2008 - Bug discovered
May 14th, 2008 - Vendor contacted and the start of a syncronized
code patching
May 16th, 2008 - MU trunk code fixed
July 28th, 2008 - WPMU 2.6 released
September 2nd, 2008 - WPMU 2.6.1 released
September 29th, 2008 - Security advisory released


IV. Solution

Upgrade to version 2.6 or upper of wordpress multi-user. It can be
downloaded from http://mu.wordpress.org


V. Credits

Juan Galiana Lara