Security researchers have identified serious security concerns with widely-used Internet telephony equipment from networking giant Cisco.

According to tests conducted by pen testing outfit Secure Test on its own VoIP network, Cisco 7900 VoIP phones are susceptible to both DoS attacks and communications interception vulnerabilities. Cisco 1760 VoIP routers can be crashed with malicious traffic, the tests further revealed.

A posting to BugTraq on the issue stated that Cisco had addressed these vulnerabilities with an upgrade to its VoIP "server software", Cisco Call Manager Release 3.3(3).

Secure Test disputes this and says the vulnerabilities are yet to be addressed more than six months after it first notified the networking giant of the problem.

We put this point to Cisco over a week ago. Despite repeated requests for comment, including one made during a visit by The Register to its UK headquarters early this week, it has yet to respond.

Ken Munroe, managing director of Secure Test, said that Cisco might have to issue a firmware upgrade to address the problems it has found.

The issue stems from protocol handling problems that mean VoIP kit is vulnerable to types of attacks (such as ARP spoofing) more frequently thrown against data networks.

Although Secure Test has not performed tests on other vendors’ hardware; it reckons VoIP equipment from other suppliers might also be vulnerable.

Wil [sic] Allsopp, a security researcher at Secure Test, said the security shortcomings it has identified open the way up to man-in-the-middle attacks. This in turn would allow everything from data interception to packet injection, he added.

"This means that many VoIP phones can be tapped by anyone else with a phone on the same network. Any individual VoIP phone can be crashed easily and VoIP networks are vulnerable to DoS attack," Allsopp told The Register.

A senior BT security expert said this threat is greatly reduced by the fact that enterprises almost exclusively deploy internet telephony over corporate intranets, so these networks are protected by corporate firewalls. Secure Test counters that hackers could get around this protection by launching an attack from an internal PC contaminated with a Trojan.

Secure Test reckons many VoIP network infrastructures are heavily vulnerable to DoS attack.

"It is clear that transferring phone systems to an IP network opens them up to many of the same security concerns as data networks. More worryingly, phone systems may be harder or even impossible to patch," Secure Test warns.

Neil Barrett, technical director of security consultants Information Risk Management, agreed that VoIP networks were hard to secure.

"Securing a soft PBX is something of a black art. These devices are difficult to secure because they straddle organisational boundaries. VoIP systems are often not as well protected as other elements in a data network," Barrett noted. ®