Summary
The remote host is running vBulletin, a web based bulletin board system written in PHP.
The remote version of this software seems to be prior or equal to version 2.3.5 or 3.0.5.
These versions are vulnerable to a cross-site scripting issue, due to a failure of the application to properly sanitize user-supplied URI input.
As a result of this vulnerability, it is possible for a remote attacker to create a malicious link containing script code that will be executed in the browser of an unsuspecting user when followed.
This may facilitate the theft of cookie-based authentication credentials as well as other attacks.
Solution
Upgrade to versoin 2.3.6 or 3.0.6