Netgate pfSense CE through 2.9.0 contains a configuration injection vulnerability that allows authenticated WebGUI users to inject mpd5 commands by submitting an unescaped RADIUS shared secret. Attackers with L2TP or PPPoE Server edit privileges can POST a secret containing a quote and newline to vpn_l2tp.php or services_pppoe_edit.php, appending an up-script that executes as root when a session starts.