Devdas Bhagat said:
" everything which is not known good is bad. Any security policy
which attempts to enforce otherwise is broken"
The problem is that earlier understandings of "known good" such as "follows the
protocol exactly and does not use any unsafe commands in the protocol", which is
what a proxy firewall implements are not complete. The "known good" paradigm is
not as simple as it appears on the surface. Because of problems in actual
implementations of protocols on servers and workstations, there is now the
problem that "known good" for Apache web servers may be bad for Windows IIS
servers. So there needs to be a finer resolution of "known good" than most proxy
firewalls can handle. The technology used to develop IDS has more of that finer
resolution than most present firewalls, whether proxy or not. So taking the
analysis technology from IDS and adding it to a secondary firewall called an IPS
(as well as to application specific firewalls) helps add to the security policy.
It would be nice if proxy firewalls were more accurate in identifying "known
good" traffic, but the complexity that adds to a choke point would make the
firewall a risk in itself.
By having separate systems in a layered approach, one can separate the
firewall that only passes valid safe protocol traffic but doesn't know about
particular flaws in particular implementations from the IPS that protects a
particular implementation of that protocol by ensuring only safe traffic for
that implementation. That separation of roles can provide better "defence in
depth" than either one alone.
-----Original Message-----
From: Devdas Bhagat [mailto:devdas@dvb.homelinux.org]
Sent: Monday, July 25, 2005 3:31 PM
To: focus-ids@securityfocus.com
Subject: [Bulk] Re: Firewalls (was Re: IDS evaluations procedures)
On 22/07/05 14:32 -0700, Swift, David wrote:
Right up front, I'll admit I work for a vendor, but...
1. There are a growing number Intrusion Detection/Intrusion Prevention
Systems that have integrated firewall.
2. IPS is a significant step in the right direction, and does things a
firewall can't. If you have doubts, try using Firewalker to pinpoint
Only if your "firewall" is a pure packet filter. Why not improve the IPS
to disallow all traffic except that which is found to be legitimate. The
subset of all traffic which is legitimate is far smaller and
deterministic. And then you might as well terminate the connection right
there and build a wholly new one which is known to be good. And then
market it as a proxy?
<snip>
Oh, and by the way while you have the data payload open for inspection,
why not apply intelligent rules to look for MalWare in the payload? Then
toss the bad payload packets away with everything else you've already
filtered with the firewall rules.
I repeat: everything which is not known good is bad. Any security policy
which attempts to enforce otherwise is broken.
Oh well, history repeats itself.
Devdas Bhagat
------------------------------------------------------------------------
Test Your IDS
Is your IDS deployed correctly?
Find out quickly and easily by testing it
with real-world attacks from CORE IMPACT.
Go to http://www.securityfocus.com/sponsor/CoreSecurity_focus-ids_040708
to learn more.
------------------------------------------------------------------------
