source: http://www.securityfocus.com/bid/8426/info

A vulnerability has been reported for Poster.version:two. The problem occurs due to the application failing to lock the 'setup' variable after initialization. As a result, an attacker may access this variable to add additional adminstrator users to the forum. This may effectively allow for the theft or modification of sensitive information. 

http://www.example.com/poster/?go=setup_submit&un=DarkKnight&pw=123456&em=EMAIL&submit=submit