PIX, Nessus and the ip_id field in IP packets

Unanswered Question

When I scan the interface ip address of a PIX (version with Nessus, I'm shown a Security Issue Warning refering to non-random ip id values in the ip_id field in IP packets. Some research indicates that this can be used for:

stealth os fingerprinting

anti-spoofing rule discovery

stealth scanning

Does the PIX use non-random ip id values?

Is this something that I should be concerned about?

If not what defense does the PIX have against these exploits.

Thanks in advance,


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shannong Mon, 03/10/2003 - 17:21
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These aren't exploits. Exploits are used to compromise a host. These are information discovery techniques.

My mistake, you're right, this is an information discovery technique not a vulnerability. I still have some questions though:

Does the PIX use non-random ip id values?

Should I be concerned about this?

How does the PIX respond to this type of reconnaissance technique?

Can I or do I have to configure the PIX to defend against being used for or subject to this type of discovery?


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