source: https://www.securityfocus.com/bid/14390/info

NETonE PHPBook is prone to a cross-site scripting vulnerability because the application fails to properly sanitize user-supplied input to the 'admin' parameter of the 'guestbook.php' script.

A successful exploit could allow an attacker to steal cookie-based authentication credentials and launch other attacks. 

http://www.example/com/guestbook.php?admin="><script>alert(document.cookie)</script><!--