source: http://www.securityfocus.com/bid/13483/info

Invision Power Board is prone to a cross-site scripting vulnerability. This issue is due to a failure in the application to properly sanitize user-supplied input.

An attacker may leverage this issue to have arbitrary script code executed in the browser of an unsuspecting user. This may facilitate the theft of cookie-based authentication credentials as well as other attacks.

It is reported this issue may only be exploitable through Microsoft Internet Explorer; this has not been confirmed. 

http://www.example.com/index.php?act='><script>alert(document.cookie)</script>