RE: Layer 3 and Firewall

[Joseph McCray <joe () learnsecurityonline com>]

A Not So Related topic...

Has anyone here actually used VLAN hopping in a pen-test. Although I've
played with it in a lab I've never actually done in an audit as (at
least for me) I found it HEAVILY dependent upon terrible switch
configuration.

The .mil/.gov networks that I used to audit had fairly decent
configuration management so disabled VLAN1, blah blah blah...

On networks that didn't have all of that configuration management on the
infrastructure I'd have domain admin way before I even got close to
something like that.

Also another concern is these enterprise multi-layer switches - like we
had 4 6509 switches with redundant paths out. I just can't see doing
that kind of stuff and risking taking down the ENTIRE network.

What do you guyz think?

Joe






On Thu, 2006-10-05 at 14:14 -0400, Paul Melson wrote:
> -----Original Message-----
> Subject: Layer 3 and Firewall
>
> > Is it a BAD idea to have multiple logical segments of a Firewall connected
> to the same physical switch?
>
> It's not a good standard to adhere to because layer-2 VLANs can be hopped in
> some cases by attacking the switch, but the level and type of vulnerability
> will vary by implementation.  
>
> In fact, Check Point is designed so that you can have multiple virtual
> interfaces on a single physical port by using 802.1q VLAN tagging.
>
> > The threat I see is if the network switch administrator wants to bypass
> Firewall, he can just disconnect 
> > the Firewall links and make the VLANs Layer 3 and there is no security.
> After malicious activites he can 
> > very well connect the Firewall and revert back to Layer 2.
>
> This is a separate issue.  If the switch admin is not in sync with the
> firewall admin or cannot be trusted, then 1) yes this is a valid threat and
> 2) while a technical solution exists, the best solution to this specific
> issue is to address these problems from a personnel perspective and either
> reassign responsibility for those switches or replace the switch admin with
> someone who is trustworthy.
>
> > Is that a valid threat ? Is it High risk ? What controls are possible ?
> Are multiple physical switches 
> > required.?
>
> Probably the thing to do would be to research whether or not a workstation
> on either VLAN can hop to the other with the current switch configuration.
> You're going to want yersinia, Cain, arptools and another Cisco switch (a
> 2950 is fine for this) and see if you can flood or spoof your way to the
> other VLAN.  This is best done during a maintenance window or some time when
> it's OK to disrupt the network.
>
> PaulM
>
>
>
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-- 
Joe McCray
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Email:      joe () learnsecurityonline com
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