pfSense, a free BSD based open source firewall distribution, version <= 2.2.6 contains a remote command execution vulnerability post authentication in the _rrd_graph_img.php page. The vulnerability occurs via the graph GET parameter. A non-administrative authenticated attacker can inject arbitrary operating system commands and execute them as the root user. Verified against 2.2.6, 2.2.5, and 2.1.3.