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

VoIP Threat Taxonomy Scope of our research Refer to for more details on this taxonomyhttp://

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 SIP RTP Filter IFilter II VoIP Traffic Attack Traffic Untrusted DPPM sipd Trusted SIP 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 112, % 5012, % 10012,0001,33110, % 1006,0001,2524, % 1004,0001,3442, % 1002,0001, % 2002,0001, % 3002,0001, %

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)