From Forbes.com:

Apr. 12 2011 - 10:36 am
Study Finds Firewalls From Cisco, Fortinet, Others Vulnerable To Old Attack
Firewalls are meant to function as the definitive filter between the inside and outside of a company's network. But a known attack still allows hackers to easily bypass firewalls sold by five out of six major vendors.

That's one finding of a study by NSS Labs, a Carlsbad, Calif.-based independent auditing firm that on Tuesday published results from a performance and security study of firewalls from Cisco, Fortinet, Juniper, Palo Alto Networks, SonicWALL and Check Point. Every one of those companies' firewalls-with the notable exception of Check Point–remains vulnerable to a trick called TCP Split Handshake spoofing.