Re: IP Telephony pen-test and VLAN's

[Jason Ostrom <justiceguy () pobox com>]

Frank,

Unless the access switch uses 802.1x port security, there is no 
negotiation via CDP for allowing your PC access to the voice VLAN.  What 
you need to do is configure your PC to add a 802.1q VLAN tag to your 
ethernet frame, use the Voice VLAN value, and then your PC will 
broadcast a DHCP request with the correct VLAN tag.  The access switch 
will allow, and your machine will obtain a DHCP address on the voice 
VLAN, etc.

I do not know of a tool to do this in Windows, but in Linux, it is trivial:
http://linux-ip.net/html/ether-vlan.html

For injecting ARP MITM and using Cain & Abel, you might have a local 
configuration issue.  In my testing, you didn't need to Hop into the 
Voice VLAN in order to sniff voice traffic with Cain & Abel.  Is your PC 
 terminated ethernet into the back of the IP Phone, or into the wall?

By the way, there was a security notice discovered by Jake Reynolds with 
Fishnet Security regarding bypassing 802.1x controls and gaining access 
to the voice VLAN via spoofing CDP.  Somewhat similar to your situation, 
but it should be a non-issue.

http://www.fishnetsecurity.com/csirt/disclosure/cisco/Cisco+802.1x+Advisory.aspx

All the best,
Jason Ostrom

Frank Bussink wrote:
> Hello,
>
> I'm trying to do a pen-test on a Cisco IPT system.
>
> Cisco IP telephone are connected on the same network cable as the PC, but
> are working on another vlan.
> The access switches have a configuration like :
> switchport mode access
> switchport access vlan 123
> switchport voice vlan 124
>
> I think the negotation with the access switch is done by CDP but I'm not 
> sure.
>
> Does anyone have a tool that emulates the PC as a voice device in order 
> to receive a dhcp lease on vlan 124, so I can start to inject ARP MITM 
> with Cain for example ?
>
> Kind regards
> Frank
>
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Concerned about Web Application Security? 
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Choice Award from eWeek. As attacks through web applications continue to rise, 
you need to proactively protect your applications from hackers. Cenzic has the 
most comprehensive solutions to meet your application security penetration 
testing and vulnerability management needs. You have an option to go with a 
managed service (Cenzic ClickToSecure) or an enterprise software 
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