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
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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