source: http://www.securityfocus.com/bid/28866/info

SMF (Simple Machine Forum) is prone to a security-bypass vulnerability that occurs in the audio CAPTCHA protocol.

Successfully exploiting this issue may allow attackers to send unsolicited spam or perform other automated attacks.

https://github.com/offensive-security/exploit-database-bin-sploits/raw/master/sploits/31678.zip