[Snort-users] RE: NAT Penetration Techniques

Basil Saragoza snortlst at ...125...
Wed Mar 6 11:44:49 EST 2002

Would it be correct to say that (theoretically at least)
If I see in snort lan sensor attacks on my lan workstations it mostly means
that the 'initiator' is local workstation and not the external address cause
people from outside wouldn't know that ws ip is This is the
indication that trafic was routed back to that 'initating' lan workstation,
and not indication that someone somehow bypasses my NAT on fw.
----- Original Message -----
From: "Jeff DuVall" <abyssleaper at ...125...>
To: <snort-users at lists.sourceforge.net>
Sent: Wednesday, March 06, 2002 1:32 PM
Subject: [Snort-users] RE: NAT Penetration Techniques

> While I'm not an expert at NAT/Penetration/SNORT, I might be able to shed
> some light for you.  I have a similar setup where my Firewall NAT's all
> connections to the outside world. For example, I might have 10 connections
> to the outside world from the following 10 imaginary internal IP's:
> ..
> and they will all appear to the outside world as (if that is my
> public NAT ip)  You firewall keeps track of which internal IP's have
> initiated a connection, and routes the traffic to the correct workstation,
> even though you have NAT in place.  The reason you are seeing these alerts
> is due to the fact that your firewall is re-routing the packets to the
> correct IP, and your internal Snort is giving you the alert on the payload
> contained in that packet.  The external sources dont' have any idea what
> your internal addresses, and couldn't use  them unless they had access to
> your internal network.
> On my system, the majority of the shellcode alerts are false, as the
> signature is picking up on HTML code from normal web traffic.
> Just my thoughts here..
> -Jeff
> <..snip..>
> >From: "Basil Saragoza" <snortlst at ...125...>
> >To: <snort-users at lists.sourceforge.net>
> >Date: Tue, 5 Mar 2002 18:24:30 -0500
> >Subject: [Snort-users] NAT penetration techniques
> >
> >I'm not really sure this forum is a plcae to ask those questions, but
> > >maybe
> >you can give me a hint...
> >I run 2 snort sensors: first sniffs traffic coming to public ip of the
> >firewall, second sniffs the lan ip of the firewall, so I can see which
> >traffic comes from the internet and which one is actually penetrated
> > >inside
> >my lan through firewall.
> >
> >I shellcode atacks and other icmp activity that are directed to
> >inside my lan - some workstations let'say. Some of those workstations
> >dhcp ip address and some have static (from 10.0.0.x range).Those
> >workstations ip addresses use hidden NAT when they go to internet and
> >outside worls has knowledge of the hidden nat ip address but not of teh
> >particular 10.something address.That's my understanding.....
> >In snort I see attackes directed to 10.0.0.x addresses.
> >AND
> >thx.
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