dhcpcd is an RFC2131 and RFC1541 compliant DHCP client daemon.
dhcpcd has the ability to execute an external script named
/sbin/dhcpcd-<interface>.exe when assigning a new IP address to a network
interface. This script sources a file named
/var/lib/dhcpcd/dhcpcd-<interface>.info that contains several shell
variables and assigments with DHCP information.
Simon Kelley pointed out a vulnerability in the way quotes inside these
assignments are treated. By exploiting this, a malicious DHCP server (or
attackers able to spoof DHCP responses) can execute arbitrary shell
commands on the DHCP client (which is run by root).
