Despite warnings that VoIP is vulnerable to a new breed of attacks, the biggest threat to VoIP remains weaknesses in general network security, according to a vendor presentation at the RSA Security Conference 2006.

Experts are aware of possible attacks that could be made against VoIP protocols, but worms, viruses and other exploits that take down servers or congest networks in general are the exploits that hurt VoIP in practice, says David Endler, chairman of the VoIP Security Alliance (VOIPSA) and director of security research for 3Com's TippingPoint division.

Analysis of IP voice components is key to keeping VoIP networks secure, he says. For instance, some IP PBXs are based on Windows, so any security flaws in Windows are security flaws in the voice network.

Customers should check the management platforms of IP voice gear as well, Endler says. For instance, some management uses TFTP protocol, which requires no authentication, so hackers could glean information about the VoIP network that could be valuable in itself or provide information for future attacks, he says.

Some VoIP phones include packet capture features that are useful in tracing packets to analyze network performance. But in the wrong hands a network of phones with this feature could be used to sniff networks for sensitive traffic such as passwords, he says. "This could be problem especially if the phones are connected to a hub," where they could view all traffic passing through.

Logically segmenting VoIP traffic on its own VLAN can help keep it clear of attacks against data traffic, he says.

To protect VoIP networks, Endler recommends:

* Patching gear regularly against known threats.
* Changing default passwords on all gear.
* Following vendors' check lists for securing gear when installed.
* Using intrusion prevention gear.
* Using VoIP aware firewalls to protect IP PBXs.

Attacks against VoIP in particular are coming and probably soon, he says, but no one can be sure when. One likely form of attack will be fuzzing, the practice of sending malformed packets within VoIP protocols. For example, putting a string of integers in a packet when the protocol expects letters might cause IP PBXs to shut down. Methodical testing of VoIP protocols with such malformed packets at Finland's University of Oulu have already revealed some such vulnerabilities, he says.