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 website, potentially allowing for the 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 versions 3.0.12 through 3.5.3. Other versions may also be affected.