Protecting VoIP networks against denial of service and service theft

Henning Schulzrinne

with Gaston Ormazabal (Verizon) and IRT graduate students

Dept. of Computer Science

Columbia University

March 30, 2007

VoIP is Different

• No retransmission for voice data --> no recovery of lost data• Real time application --> delay must be below 150 ms• Merges traditional PSTN networks with IP --> new avenues for attacks on IP networks

and PSTN• Optimize security overhead such that it doesn’t impact delays• Billing in VoIP services is different from PSTN

– flat rate billing– multiple extensions

Diagram from http://www.sipera.com

VoIP Threat Taxonomy

Scope of our research

Refer to http://www.voipsa.org for more details on this taxonomy

Scope of Our Research

Scope of current work

Previous Work

• Successfully implemented a large scale SIP-aware Firewall (using dynamic pinhole filtering)

– The filter is used as a first-line of defence against DoS attacks at the network perimeter and it enforces the following:

• Only signalled media channels can traverse the perimeter• End systems are protected against flooding of random RTP or

other attacks.

• The RTP pinhole filtering approach is a good first-line of defense but…

– The signalling port (5060) is subject to attack on the signalling infrastructure

– This lead us to define the new problem...

VoIP Traffic

Attack Traffic

Untrusted

DPPM sipd

Trusted

SIPSIP SIP

RTP RTP

Filter I Filter II

VoIP Traffic

Attack Traffic

Untrusted

DPPM sipd

Trusted

SIPSIP SIP

RTP RTP

Filter I Filter II

Mitigation Solution Overview

Testing Results – With the Return Routability filter

Call Rate (calls/sec) No. of Concurrent calls (load)

Number of calls setup

Number of calls dropped

% calls dropped

1 12,000 12,000 0 0.0%

50 12,000 12,000 0 0.0%

100 12,000 1,331 10,669 88.9%

100 6,000 1,252 4,748 79.1%

100 4,000 1,344 2,656 66.4%

100 2,000 1,922 78 3.9%

200 2,000 1,884 116 5.8%

300 2,000 1,800 200 10%

Theft of Service• Theft of service causes lost revenue and bad reputation

– resources are abused causing monetary losses– unauthorized usage can degrade whole system’s performance

• Related theft of services attacks:– distributed denial of service on billing system– spoofing, content alteration, intrusion, platform attacks

• Checks to perform before establishing session:– enough funds, 800 numbers, emergency number– multimedia services, messages, etc.

• Possible theft of service scenarios:– using services without paying– illegal resource sharing for unlimited plans– compromised systems -- use third-party services– call spoofing and “vishing”

• Currently developing a test tool to identify weaknesses in deployed systems and lab prototypes

Benefits to Verizon and Columbia

• Technology Transfer to Verizon Labs– Set up a replica of Columbia testbed in Silver Spring VoIP lab for

rapid SBC evaluation

• Licensing Agreement with CloudShield– Currently negotiating a Royalty Agreement to take technology to

market

• Intellectual Property – Patents and Publications (NANOG)