Here's what I would do:

Just temporarily disconnect your Linux gateway from the Internet, set up a
small LAN on the other side (connected to your outside interface). You can
even leave the public IP address the same since you're disconnected (you may
have to make your IP static if you're DHCP). If you don't have another hub,
you can just connect your box running Nessus to your firewall's outside
interface with a crossover cable.

Then hammer it with Nessus. Should give you the same results.

-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Jerome Iffrig
Sent: Thursday, August 29, 2002 5:37 AM
To: Renaud Deraison; [EMAIL PROTECTED]
Subject: RE: == Checkin security of the inside but I am not outside bla,
bla, bla ... ==


My point was: If I run NESSUS server on the same server as the one to be
tested (against external attacks), the same server that insure the
connection from the internal network to the external world (www) and which
is protected by a firewall, any packet sent by NESSUS in purpose of the
checking have great chances to be stopped by the firewall in either sides:
IN and/or OUT - In this environment, in my understanding NESSUS cannot do
its job correctly - This is why I was thinking that nessusd HAD to run on a
separate machine, completely outside of my network (e.g. an other internet
connection for an other linux box which wont have a firewall at all in the
duration of the testing [e.g. a "crash test machine" as this poor thing wont
be protected by any firewall out there]).

Basically my understanding problem is the following: How can I pretend to
"attack" myself from the outside when nessusd in running on the server
INSIDE the firewall (note that some iptables rules might not only stop
packets from getting inside the internal network, but also stop packets
willing to go out)

Thanks for any clarification on my lake of understanding

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On
Behalf Of Renaud Deraison
Sent: Thursday, August 29, 2002 12:49 PM
To: [EMAIL PROTECTED]
Subject: Re: == Checkin security of the inside but I am not outside bla,
bla, bla ... ==

On Thu, Aug 29, 2002 at 12:48:54PM +0200, Jerome Iffrig wrote:
>    I would like to do it as if I was someone from the outside - However I
>    have installed NESSUS on the server machine which runs the firewall -
As
>    far as I understand Nessus cannot operate properly in this environment.

It will operate properly, although it will see more things than what are
actually available (if your firewall blocks all incoming connections
but you still run a vulnerable lpd or whatever, Nessus will see that
although an attacker would not).

>    So, what is the recommended approach for the tests I want to do?

Test it and upgrade everything anyway, even if not available from the
outside. If you can't break into that host from the inside, odds are
that it will be difficult to do from the outside.


                                -- Renaud
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