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Re: Port-Knocking vulnerabilities?
From: Ansgar -59cobalt- Wiechers <bugtraq () planetcobalt net>
Date: Fri, 28 Dec 2007 19:42:25 +0100

On 2007-12-28 Kappa Alpha Pi Eta wrote:
so I read this thread about port-knocking (altough called "reflexsive
firewalls"). I'd never heard of that and found that to be an very
interesting mechanism. Now I just keep wondering, what an attacker
could possibly do to intrude system secured in such a way. So there
are no open ports at all, also, there's no way the attacker could
access the computer physically or via social engineering. The attacker
knows that a knock-server is running and that there's some daemon
waiting to become accessible (what ever that may be).

Port knocking is not a security but merely an obfuscation measure, as it
just hides services from people who don't know about the measure.

What could a attacker do to somehow get access to that machine?

Knock.

And how can I secure that machine from that kind of attacks.

Just like you would secure it when not using port-knocking:

- Don't have services listening on external interfaces that shouldn't be
  accessible from the outside.
- Keep your system patched.
- Use authentication where applicable.
- Prefer public key authentication over password authentication.
...

Regards
Ansgar Wiechers
-- 
"All vulnerabilities deserve a public fear period prior to patches
becoming available."
--Jason Coombs on Bugtraq


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