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Re: Nmap/netwag problem.
From: Rogan Dawes <discard () dawes za net>
Date: Thu, 11 Aug 2005 08:09:05 +0200

Pete Herzog wrote:
Kaj,


Anyway. a 'full connect' scan (one that performs the complete three-way
handshake will _always_ (?) be the most reliable.
My sugeestion is to perform either a nmap connect scan on the ports from
both results or to manually telnet to the ports and see the response.


I have to disagree with you here.  A full connect scan is not the most
reliable.  There are many security defensive processes now which require
proper protocol queries to provide a response- I see this very often
with web ports.  If you send anything other than a http request, you
will not see a service behind the web port.

Excuse me? Are you suggesting that if I send a Syn to port 80, and don't get a Syn/Ack back, I should just go ahead and send a "GET / HTTP/1.0", in case there is some kind of application level firewall that will only pass my original Syn if it sees a valid HTTP request following it?

Sounds like someone is redefining TCP, to me!

I can't imagine any TCP/IP implementation (bar Microsoft, of course!) that would be so braindead, and would actually do anything further if the Syn/Ack was never received.

At the very least, once the full TCP connect scan has identified that there IS a service running on a particular port, you can then try to identify the service by prodding it with various protocols, and seeing which respond. I certainly agree with your statement that many services do not respond with layer 4 (?) protocol data, if the input is not well-formed.

But the original statement was with regards to identifying that a (ANY) service is actually listening on a particular port. And I tend to agree that a full connect scan is more reliable than a Syn scan.

Regards,

Rogan

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