source: http://www.securityfocus.com/bid/9822/info

It has been reported that Invision Power Board may be prone to a cross-site scripting vulnerability. This may allow a remote attacker to cause hostile HTML or script code to be rendered in a user's browser via a malicious link to a vulnerable site.. The issue presents itself due to insufficient sanitization of user-supplied data via the 'pop' URI parameter, which will be included in dynamically generated web pages.

Invision Power Board 1.3 Final has been reported to be affected by this issue, however, it is possible that other versions are vulnerable as well.

http://<host>/forum//index.php?s=&act=chat&pop=1;'><script>alert('this could be your cookie')</script>