VOIP-Specific Attacks Not an Issue Yet

Collier and Endler recommend that enterprises have a security assessment done by an outside expert when implementing VOIP on their networks. And, Endler said, they have a list of 10 or so best practices, such as enabling encryption to prevent eavesdropping, changing default passwords, applying patches in a timely manner, separating voice traffic into its own virtual LAN, and implementing VOIP-aware firewalls that can open and close ports dynamically.

Collier also recommends enabling logging on critical equipment in the network, so that if there is an attack, it's "a lot easier to figure out what happened," he said.

And they suggest using the protections that are there in the vendors' products.  Market leaders such as Cisco, Avaya and Nortel all continue to step up to the plate in securing their VOIP offerings.

"I think their systems are pretty secure. They've stepped up," said Collier.

There are known vulnerabilities in different vendors' VOIP products, but those are addressed by Tipping Point and competitive products, which take two approaches to securing VOIP. "We research [the vulnerabilities], bake that intelligence into our products, which see the [offending] traffic, and block it in real time. The other approach is applying knowledge of VOIP protocols and applying anomaly detection," Endler said.

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For example, SIP (Session Initiation Protocol) packet headers are never supposed to include more than 1,000 characters. "If you see a SIP packet header 5,000 characters long, you can block it," he said.

Endler believes the biggest threat to VOIP today is in quality of service, and the second biggest threat centers around infrastructure attacks against routers, DNS servers and TFTP servers. "If someone can take out your TFTP server, they can take down the VOIP network just as readily as if it were an attack on the PBX," he said.  

Still, SecureLogix sees more traditional types of attacks focused on toll fraud, unauthorized modems and backspam, Collier said.  "Only in a few cases have we found VOIP-specific attacks."

But in one toll fraud case, SecureLogix found that an attacker learned how to connect directly to a media gateway installed with one customer's VOIP system and used it to make thousands of long-distance calls that completely bypassed the IP PBX.  "It was an old world attack, but they did it in a way that's unique to VOIP," said Collier.  

While First American Bank's Duchaj is confident in the security already implemented for VOIP, he isn't sitting back and waiting for a VOIP-specific attack to happen.

"I think in the next 18 to 24 months we'll have to do more to protect VOIP traffic," he said.  That includes implementing Cisco's Network Access Control products, and as the bank moves to implement SIP trunking, Duchaj will look to do more to lock down VOIP traffic. "We'll look into Secure RTP and transport layer security," he said.