source: https://www.securityfocus.com/bid/16878/info

PHP is prone to multiple input-validation vulnerabilities that could allow 'safe_mode' and 'open_basedir' security settings to be bypassed. These issues reside in the 'mb_send_mail()' function, the 'mail()' function, and various PHP IMAP functions.

mb_send_mail($email_address, NULL, NULL, NULL, $additional_param);