This sort of attack reinforces the need of host level security, even
if you have a firewall protecting your network. Some people think
they do not need to apply security patches to machines inside the
firewall, but if those patches were in place, then it would be more
difficult for the intruder to gain root on compromised machines.
(Note I said more difficult, not impossible).
What is the phrase used? A firewall is a hard, crunchy exterior, but
be sure not to have a soft, chewy inside just in case the exterior
gets cracked somehow.
DISCLAIMER: I speak for myself, not my employers.