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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