Security vendor Fortinet has hit back against tests by NSS Labs that showed one of its high-end firewalls along with products from other vendors could be hacked using a 'TCP split handshake attack'.According to a statement put out by Fortinet, its Fortigate-3950B was only vulnerable to this attack if used independently of the Intrusion Prevention System (IPS) and anti-virus modules, which by implication would be the company's recommended configuration.Furthermore, Fortinet said, the company had developed IPS signatures to block this type of attack and would also modify its firewall functionality to do the same.Six vendors were assessed by NSS Labs - Fortinet, SonicWall, Palo Alto Networks, Juniper, Cisco and Check Point - which got hold of the kit from companies using the equipment rather than the vendors themselves. This overcomes the valid criticism that many equipment tests are not independent because the participating companies pay for them to be conducted.Only one product out of six resisted this potentially serious spoofing attack, Check Point's Power-1 11065."We feel strongly that integrated protection is the best approach for blocking this issue, as customers that have IPS working with their firewall are better protected against a wider range of threats. The majority of Fortinet's customers are using integrated firewall and IPS, as well as other security feature," said Fortinet VP of product marketing, Patrick Bedwell."The IPS signature is a short-term work around to the split handshake, and provides immediate protection against this issue. Customers can enable a single IPS signature if they are not currently running the IPS feature that is included in the FortiGate consolidated security platform," he added.Does the company's reasoning hold any water?Fortinet has some justification in pointing out that many customers buy its firewalls to use at multi-module Unified Threat management (UTM) appliances and so would almost certainly have more than one module turned on at once. Fortinet counts as a pioneer of this multi-purpose model of security.On the other hand, that the firewall component of a system is vulnerable in five out of six vendors' systems tested is damning. Would the issue have been discovered or at least disclosed had NSS labs not conducted its tests independently of the vendors? Almost certainly not. Certainly the security of one element of a UTM should not be dependent on the use of other modules at the same time.Fortinet said it planned a firmware update for the FortiOS UTM operating system for later this year.