Sebastian Krahmer and Marius Tomaschewski discovered that dhclient of isc-dhcp, a DHCP client, is not properly filtering shell meta-characters in certain options in DHCP server responses. These options are reused in an insecure fashion by dhclient scripts. This allows an attacker to execute arbitrary commands with the privileges of such a process by sending crafted DHCP options to a client using a rogue server.