source: http://www.securityfocus.com/bid/16116/info

vBulletin is prone to an HTML injection vulnerability. This issue is due to a failure in the application to properly sanitize user-supplied input before using it in dynamically generated content.

Attacker-supplied HTML and script code would be executed in the context of the affected Web site, potentially allowing for theft of cookie-based authentication credentials. An attacker could also exploit this issue to control how the site is rendered to the user; other attacks are also possible.

This issue is reported to affect vBulletin 3.5.2. Earlier versions may also be affected. 

The following example was provided as Event Title input:

TITLE:--------->Test<script>alert(document.cookie)</script>