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Home > Security > Other Considerations On TCP Split Handshake

Other Considerations On TCP Split Handshake


The storm unleashed by NSS Labs test for the TCP split handshake attack which affected 5 firewall vendors  is far from being quiet.

During these days I enjoyed speaking with many colleagues about the results of the tests and definitively, I must confess that firewalls were not the only entities unaware the TCP Split Handshake, as a matter of fact, none of the professionals I discussed with (of course including me the first time I read about it) were familiar with this method of establishing TCP connections.

Nevertheless the show must go on: professionals must study to stay up-to-date (and learn what TCP Split Handshake is), firewalls (if susceptible to attack) must be fixed in order to learn how TCP Split handshake is correctly handled.

After the surprising findings of the test vendor are running for cover, so I spent half an hour to check the state-of-the-art after some communications from NSS Labs (unfortunately I was not able to attend the webinar of today) and some rumors on the Infosec arena.

Among the manufacturers found susceptible to TCP Split handshake attack during the first round, Palo Alto Networks has released an update (4.0.2) to fix the TCP Split Handshake Evasion, after the fix the manufacturer was able to pass the TCP handshake attack test.

As far as Juniper Networks is concerned, today a communication sent by E-mail by NSS Labs has indicated that this vendor is working on a fix as well: a configuration setting which will be enabled by default for new customers.

But probably the most interesting piece of news is the fact that today some Cisco representatives today went to NSS Labs to participate in the vulnerability-assessment on site and sort out any issues directly. Cisco refused to accept the results of the tests since was not able to reproduce the issue on any tested platform (ASA, IOS Firewall, IPS Appliances). An updated blog post about the findings is expected later today. NSS Labs also expects to publish updated findings related to what firewalls it tested have completed remediation to protect against the TCP Split Handshake attack.

Just for fun…

(But not only!), I gave a look individually to other vendors not involved in the tests to see if they had analyzed the behavior of their technologies on this issue.

Some McAfee representatives indicated me that their Enterprise Firewall platform is not prone to TCP Split Handshake attack. I looked for some information and I found this post from the vendor. Would be interesting if the security manufacturer from Santa Clara could release a more detailed documentation (maybe they already released but I did not find it J).

Stonesoft issued a blog post with the result of the test performed individually on its Stonegate Devices with the same BreakingPoint method pointed out in the original document describing the attack. The finding is that with the only firewall function the security device is not vulnerable if the “strict mode” is enabled in the advanced properties of the node. In normal or loose mode the traffic is permitted (even if Stonesoft indicates that the firewall does not get spoofed, that is correctly recognizes the origin of the session). With the antivirus function enabled the firewall is not vulnerable in any mode.

Astaro except some tweets indicating that the technology is not vulnerable. Would be interesting, also in this case, if the vendor could release some detailed document on the necessary configurations to be implemented to avoid the spoof (or if they are enabled by default).

I was nearly forgetting Microsoft, for which there is not any official document. Anyway I found an independent test in this blog which seems to confirm that the Microsoft platform is not vulnerable.

At this point I look forward to read the result of Cisco/NSS joint tests…

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