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Mike Riley

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Hacking VoIP Book Review

November 15, 2008

Having implemented and customized Asterisk-based VoIP solutions in the past, I was already aware of potential security issues around Voice over IP, especially using SIP.  So it was with great curiosity to read about author Himanshu Dwived's VoIP-hacking investigations.
This 10 chapter, 200+ page book opens with setting up a test environment to experiment and understand VoIP attack vectors using the Session Initiated Protocol (SIP), RTP (Real-time Transport Protocol), H.323 and IAX (Inter-Asterisk eXchange) communication mechanisms.  After a brief overview of basic VoIP security measures, the book leads into the first half with a on a deep dive into these VoIP protocols.  SIP is the first protocol brought under scrutiny due to its growing popularity.  With that comes SIP's glaringly weak security standards, so weak that it's rare to find corporate SIP services shared outside a corporate firewalled environment.  The SIP attack vectors demonstrated in the book are somewhat obvious to anyone who has worked with SIP-based services, and sniff and crack tools like Cain & Abel and Wireshark are well-known in network security circles.  The author does uncover a few other more recent SIP vulnerability/testing tools like SIP.Tastic and SiVus and vnak.

H.323 protocol is evaluated next using the same approach as the chapter on SIP.  First, a basic review of how the protocol operates followed by how attacks including username and alias enumeration, hopping, password retrieval, replay attacks, endpoint spoofing and denial of service can be perpetrated.  The next chapter on RTP offers a wrinkle with the ability for an attacker (or legitimate application) to insert and even replace audio into an RTP session using a tool called RTPInject.  Reading this chapter offered insight as to how a product like OrecX works (check out my interview with Bruce Kaskey, cofounder of OrecX, for more about this VoIP recording application.)
Chapter 5 explores the IAX protocol in the same way, detailing dictionary, man-in-the-middle, MD5 downgrade and denial of service attacks.

The second half of the book begins with an assessment of popular VoIP services such as those from Avaya, Cisco, open-source Asterisk-based solutions and even home-based solutions like Vonage and software clients like Google Talk, Skype and Yahoo Messenger.  Unconventional threats such as email phishing attacks, caller ID spoofing, anonymous eavesdropping, VoIP SPAM and SPIT are discussed.  The book concludes with a chapter on auditing VoIP for security best practices presenting a nice three column, 8-page table listing audit topic, questions and results.

With VoIP rapidly proving to be a very cost-effective alternative to closed, proprietary network solutions, it is also shaping up to becoming the next white and black hacker battleground.  Reading Himanshu's book supplies a meaningful education on the positive and negative opportunities that the technology can deliver developers, security professionals and users alike.


Author: Himanshu Dwived
Publisher: No Starch Press
ISBN: 978-1-59327-163-3
Price: $44.95 US

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