The exec_dir PHP patch (php-exec-dir) 4.3.2 through 4.3.7 with safe mode disabled allows remote attackers to bypass restrictions and execute arbitrary commands via a backtick operator, which is not handled using the php_escape_shell_cmd function.
https://exchange.xforce.ibmcloud.com/vulnerabilities/16498
http://secunia.com/advisories/11928
http://seclists.org/fulldisclosure/2004/Jul/0357.html
http://seclists.org/fulldisclosure/2004/Jul/0350.html