Opinion: Dealing with the phone phreakers

VoIP hacking, or “phone phreaking”, is on the rise. In April, for example, Western Australia Police warned the state’s businesses to change passwords and cap international calls on enterprise VoIP networks. The reason: three businesses were reported to have had their VoIP networks hacked by opportunists who used them to make calls to international numbers. The businesses suffered losses of some £47,000 from the attacks.

Such “premium-rate” scams are not new and usually involve a bogus operation, registered outside the EU, that hacks into an unsuspecting business’ PBX then programmes the switch to make calls automatically.

Industrial competition is another area for VoIP crime. A competing company or a third-party/hacktivist breaks into a system to create a denial-of-service (DoS) attack that prevents outbound calls.

The problems have arisen because most VoIP networks interface directly with the data network. And a poorly designed one will expose you to DoS attacks, fraud, computer viruses, eavesdropping and spam. So, what can an enterprise do to thwart the phone phreakers?

To protect the network the traffic in VoIP and unified communications (UC) networks has to be separated into three distinct planes, each with its own dedicated protocols: call control - SIP protocol; media - RTP; and management - SNMP, HTTP, Telnet, Radius etc. Protocol data must also be encrypted between the endpoints and each plane has its own mechanism to do this, e.g. SIP/TLS for call control, SRTP for the media, SNMP v3 for management. And, of course, this wouldn’t work unless all the elements in the VoIP network support these security enhancements.

To further secure the network, demarcation points between “trusted” and “untrusted” domains are required, normally implemented through data firewall devices. However, for VoIP a specialist solution is needed: the Enterprise Session Border Controllers (E-SBC). The E-SBC performs functions including protocol mediation, media transcoding and facilitating interoperability between different vendors’ VoIP and legacy TDM kit. The E-SBC provides security features such as call admission control, prevention of DoS attacks, topology hiding and encryption of signalling and media.

VoIP offers many benefits but with those advantages come risks and the best way to minimise them is to ensure that security is up to the job.