[ISN] VoIP Hack Puts PCs In Peril

From: InfoSec News (alerts@private)
Date: Tue Oct 16 2007 - 22:21:30 PDT


By Thomas Claburn
October 16, 2007

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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