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10/16/2007
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VoIP Hack Puts PCs In Peril

A security researcher says attacking VoIP devices over SIP can be difficult, but many of the devices have embedded Web servers that can be hacked using a buffer overflow exploit.

There's a new way to take control of someone's PC: IP telephony.

A vulnerability found in the Linksys SPA-941 (version 5.1.8) last week by security researcher Radu State allows a malicious hacker to conduct a cross-site scripting (XSS) attack using the Session Initiation Protocol (SIP), one of the major voice-over-IP (VoIP) standards.

In a post to a security e-mail list, State notes that while attacking VoIP devices over SIP tends to be difficult because the devices in question often have custom architectures and operating systems, many of them also have embedded Web servers that can be hacked using a buffer overflow exploit.

State rates the SIP vulnerability as "very high." "Most firewalls/IPS will not protect the internal network against XSS attacks delivered over SIP," he wrote. "Additionally, users will connect to these devices directly from the internal network and therefore the internal network can be compromised."

Paul Henry, VP of technology evangelism at Secure Computing, concurs and said in a phone interview that SIP represents a blind spot for most of today's computer security products. He said that this is the first time he's seen an XSS attack over VoIP.

"I consider it to be serious because it's the first of probably what will be many attacks based on the SIP protocol," said Henry.

Henry considers VoIP to be fundamentally insecure because of the lack of real authentication of SIP devices. And he believes too many organizations want VoIP for its cost savings, and thus fail to invest in VoIP security. "Security is definitely an afterthought when it comes to VoIP," he said.

Already there have been several high-profile cases involving VoIP hacking. For example, Edwin Pena, who ran two small Miami-based VoIP telephone companies, was arrested earlier this year and charged with breaking into other VoIP services and routing calls through their lines. He allegedly made more than $1 million on the scheme.

The fact that VoIP hacking tools are freely available online will almost certainly lead to more such incidents.

Nonetheless, Henry believes steps can be taken to make VoIP more secure. He recommends application layer firewalls, reputation-based defenses, and anti-malware scanning.

While the vulnerability discovered by State applies to specific Linksys hardware, Henry suspects other VoIP devices have similar vulnerabilities. "I wouldn't be surprised to see it in more than one vendor's phone," he said. "I look at this as the tip of the iceberg."

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