The escapeshellarg function in ext/standard/exec.c in PHP before 5.4.42, 5.5.x before 5.5.26, and 5.6.x before 5.6.10 on Windows allows remote attackers to execute arbitrary OS commands via a crafted string to an application that accepts command-line arguments for a call to the PHP system function.
https://security.gentoo.org/glsa/201606-10
http://www.securitytracker.com/id/1032709
http://www.securityfocus.com/bid/75290
http://php.net/ChangeLog-5.php
http://openwall.com/lists/oss-security/2015/06/18/6
http://git.php.net/?p=php-src.git%3Ba=commit%3Bh=d2ac264ffea5ca2e85640b6736e0c7cd4ee9a4a9