source: https://www.securityfocus.com/bid/13417/info

The notes module for phpBB is prone to an SQL injection vulnerability. This issue is due to a failure in the application to properly sanitize user-supplied input before using it in an SQL query.

Successful exploitation could result in a compromise of the application, disclosure or modification of data, or may permit an attacker to exploit vulnerabilities in the underlying database implementation. 

http://www.example.com/posting_notes.php?mode=editpost&p=-99%20UNION%20SELECT%200,0,username,0,0,0,0,0,0%20FROM%20orionphpbb_users%20WHERE%20user_id=2/*