My networking guys try to do this stuff all the time--what happens when
you have too many Cisco-certified people in one room at the same time.
Do a google search for "vlan hopping" and decide for yourself it that is
enough of a risk. I think the biggest problem is that it is way too
easy to misconfigure any piece of this setup. The important thing to
say is that instead of a defense-in-depth, you're now looking at a
single device being the keystone of your security.
Since I deal with this scenario all the time, I hit upon a somewhat
compromise. I enforce hardware segregation for external/Internet-facing
vlans, but I'm OK with all the DMZ vlans being on the same switch, and
all the internal DMZs on another switch. Depending on the criticality
of the system and how much I trust the admins, I might be convinced to
do DMZ and internal together, but it's on a case-by-case basis.
HTH
--Mike
Michael J Smith, CISSP-ISSEP michael.j.smith@unisys.com
Information Security Architect
703.579.2552 O
703.855.0890 C
"Those who do not understand Unix are condemned to reinvent it, poorly."
--Henry Spencer
-----Original Message-----
From: Ng, Kenneth (US) [mailto:kenng@kpmg.com]
Sent: Monday, August 14, 2006 1:41 AM
To: cableguy clueless; pen-test@securityfocus.com
Subject: RE: Clueless firewall configuration ?
This is very difficult to set up completely correctly. And
your always open to the possibility of an unpublished exploit
being able to get around your rules. And while I do not know
if it is still possible, I remember someone demonstrating
injecting packets from one vlan to another a few years ago.
And as the infrastructure changes, you have to make double
sure that you are entirely correct. Conversely, if you use
physically separate hardware, it's a lot easier to get it right, or
close enough to right that it doesn't matter much.
-----Original Message-----
From: cableguy clueless [mailto:cluelesscableguy@gmail.com]
Sent: Friday, August 11, 2006 4:08 PM
To: pen-test@securityfocus.com
Subject: Clueless firewall configuration ?
Guys, I need to ask a favor, my boss knows nothing of IT
infrastructure, and our "cableguy" (manages the firewall
through a third party contract) proposed to him an
architecture as follows :
2 cisco 6509 each with firewall blade in them. These function
as core switches for a 1000 users site with lots of vlans and
FW roules between the vlans (oh and we are a big production
site that relies on these cores to let our ciritical
bussiness process machines communicate to the servers).
He wants to create 2 vlans, 1 for untrusted traffic and 1
vlan for DMZ machines and assign physical ports to these to
connect to the internet.
The DMZ vlan would also have some physical ports. These ports
would not be on the core switch but on the access layer
switches that are fiber attached to the distribution switches
that attach to the cores...
Does anyone care to comment on the security issues a setup as
this would pose? would this be pentest bonanza for you guys?
and what would the hackers make of a dmz vlan living in a big
switch together with other vlans?
I have some ideas myself, but would appreciate your take on
this. I know this is the pentest list but it is you guys who
get to poke holes in these designs...
CCG
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