RE: Exploit through firewall question

[<salexander () frontporch com>]

The reasons for testing behind the firewall include:

1) Firewalls can sometimes be bypassed; this is especially true of
non-stateful firewalls.  An attacker can use a UDP source port of 53
(DNS) or a TCP source port of 20 (the FTP data port).  If the firewall
allows fragments to pass, the attacker can fragment everything.

2) The attacker may gain a foothold on a publicly accessible server.
New vulnerabilities are discovered every day.  Even if there is no know
way to compromise any of your publicly accessible services, a zero-day
vulnerability could change that tomorrow.  

3) Sometimes people make changes to the firewall and screw things up.
At one place I worked, a vendor needed to be able to connect to one of
our servers in order to troubleshoot a problem with their software.
Instead of setting up a temporary VPN account or adding a temporary rule
to allow the vendor to connect to a particular port from a particular
network block, one of our network people added a rule that allowed open
access to the box from the outside and left the rule in place after the
vendor was finished.  Oops.

There is value in attacking from outside the firewall; it helps you to
determine how hackable you are from the outside right now.  But you also
need to assume that an attacker will eventually find a way to gain a
foothold into your network.  A firewall cannot be responsible for all of
your network's security.  A firewall should be used to reduce the attack
surface of your network.  There still need to be other security measures
in place behind the firewall and these measures should be assessed as
well.  Look up defense-in-depth.

Steven

-----Original Message-----
From: mr.nasty () ix netcom com [mailto:mr.nasty () ix netcom com] 
Sent: Wednesday, July 19, 2006 6:33 AM
To: pen-test () securityfocus com
Subject: Re: Exploit through firewall question

Thanks for the responses. You've confirmed what I had passed to mgmt.
But I still have a problem (with mgmt) understanding why?...


I perform vulnerability analysis on our outside (public) web presense,
usually during development and then after it's been deployed. I
basically use the same tools for each.


Mgmt wants me to only test through the firewall as if I'm coming in like
the public. The rational is that the fw will prevent any attacks though
ports other than 80 and 443. Therefore, there is no reason to change
this configuration.


What would be the reason to test behind the firewall?


Any suggestions?


Thanks

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This List Sponsored by: Cenzic

Concerned about Web Application Security?
Why not go with the #1 solution - Cenzic, the only one to win the Analyst's
Choice Award from eWeek. As attacks through web applications continue to rise,
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