Category Archives: VoIP Security Research

Amusing Vulnerability in the BT Home Hub

Building upon a previously reported (and still un-patched!) vulnerability in the BT Home Hub which allows HTTP authentication to be bypassed, the folks over at GNUCitizen recently announced a way to leverage that vulnerability to cause the Hub to steal or hijack VoIP calls if the BT customer is also using the BT Broadband Talk service:

If the victim visits our evil proof-of-concept webpage, his/her browser sends a HTTP request to the BT Home Hub’s web interface. After this, the Home Hub starts a VoIP/telephone connection to the recipient’s phone number specified in the exploit page. This is what the attack looks like: the victim’s VoIP telephone starts ringing and shows an external call message on the LCD screen along with the recipient’s phone number. However, what’s interesting is that from the point of view of the victim, it looks like he/she is receiving a phone call from the number shown on the screen, but in fact he/she is calling that number!

At the heart of the vulnerability is the fact that to the victim it appears that they are receiving a call when in fact they are actually the party placing the call. Essentially, this vulnerability can be leveraged to perform a number of attacks utilizing the BT Home Hub, such as annoyance or prank calls like the scenario described above where two unwitting people believe that each has called the other when they are connected, advanced phishing attacks such as causing the user to believe their Bank has called them, or even toll fraud in some cases where the user could be made to call pay services.

For users of the BT Home Hub and Talk Service, you can demo the exploit for yourself by visiting GNUCitizen’s Proof-of-Concept web page.

BlackHat/DEFCON VoIP Security Tools Update

There were a number of new tools released at the recent BlackHat and DEFCON conferences that I’ve just finished adding to the VoIPSA Security Tools List.

First, during the BlackHat Voice Services Security track, Himanshu Dwivedi & Zane Lackey spoke about attacks against H.323 and IAX. They released a number of tools including H225regreject, IAXHangup, IAXAuthJack, and IAX.Brute. Now you can easily launch many of the same attacks (as well as a few new ones) that you’ve known and loved from attacking SIP against both H.323 and IAX.

Next, Zane Lackey & Alex Garbutt debuted their RTPInject tool during the BlackHat turbo-talk track. It’s essentially a nice, pretty, easy to use GUI version of the RTP audio injection attack that I demoed last year at EUSecWest using the rtpinsertsound and rtpmixsound tools.

At DEFCON, Ian G. Harris released a tool called INTERSTATE which is a stateful protocol fuzzer for SIP.

Finally, I released my new RTP steganography tool, SteganRTP, at DEFCON. It uses steganographic data embedding techniques to create a covert channel in an RTP session’s audio payloads which it uses to transport it’s own custom communications protocol. The protocol provides user chat, file transfer, and remote shell access (if enabled).

All of the tools mentioned above can be found via the VoIPSA Security Tools List.

"Voice over VoIP" project aims to show use of "covert channels" to tunnel voice inside of voice

image We were contacted today by Takehiro Takahashi, a graduate research student at the Georgia Institute of Technology, who has an intriguing new research project they called “Voice over VoIP”.  From their main web page:

Vo2IP is a proof of concept attack which demonstrates a new type of VoIP threats, the VoIP covert channel. With Vo2IP, you can establish a hidden conversation by embedding further compressed voice data into regular PCM-based voice traffic (i.e. G.711 codec). Therefore anyone who is wire-tapping your conversation will decode something completely different from the actual conversation – granted that he is not aware of the use of Vo2IP.

As I understand it, they basically take a G.729 audio stream and tuck that into a spare 8Kbps that can be found in a G.711 audio stream.  An eavesdropping attacker would hear only the overall G.711 audio while the Vo2IP clients on either end encoded/decoded the covert stream (more details here and here). In any event, Takehiro and his fellow researchers would be very interested in any feedback folks have on the project.  Source and binary code for Windows is available. Please email Takehiro with any feedback.

Combatting Voice SPAM with VoIP SEAL

One of the highlights of 3GSM Barcelona for me was visiting NEC at their stand, and to see their demonstrations in action. There was some discussion in the VoIP and security space over the last weeks about a server technology called VoIP SEAL that NEC were to demonstrate at the show, and I was keen to see this in action. VoIP SEAL is a system that attempts to defend a VoIP system against VoIP SPAM or SPIT (SPAM over Internet Telephony).

Luckily, at the time I visited the stand, Saverio Niccolini of NEC was there. Saverio is a prominent researcher for NEC, and was a speaker at the 3rd Annual VoIP Security Workshop last year, which I attended and wrote about here. It was great to meet up with Saverio, and he showed me the VoIP SEAL demo himself.

To briefly summarize the system, VoIP SEAL combines a number of different techniques to detect a suspicious VoIP call. Each module does a test and produces a score or index, and at the end the indices are weighted and combined to give an overall score that measures how ‘dangerous’ a call might be. For example, there are modules that can apply blacklist or whitelist logic; measure SIP INVITE rates; test reputation or check that different SIP URIs are not coming from the same IP address. So, each module is dedicated to measuring for a particular exploit or security aspect, and they can be combined in different ways, with different weights.

An interesting part of VoIP SEAL is that it can apply tests in two phases: firstly before answering the call and then after picking up. In the first phase, the ‘suspiciousness level’ of a call can be assessed, and if the level is low, the second phase can be skipped, simply connecting the call to the recipient. However, if the level passes a configured threshold, the call is diverted to a specialized answer machine that can apply further tests. Having this two-phase approach helps to minimize false positives, where genuine human callers get trapped in the system and can’t get through.

In phase 2, VoIP SEAL can measure the speech energy when a greeting or outgoing message is being played. For a genuine human caller, this energy should be low, as humans tend to listen rather than talk over greetings. A bot or SPAM application will behave differently, perhaps starting to stream audio continuously as soon as the media channel is available. There are more sophisticated audio CAPTCHA tests (Turing Tests) that can also be applied to attempt to tell the difference between a human and a bot. If the call is considered suspicious, it can just be allowed to play its message into a voicemail SPAM queue, and perhaps this queue would be periodically reviewed by an administrator to make sure that the VoIP SEAL was working effectively and not trapping too many real human callers.

If you want to hear more about VoIP SEAL, I recorded an interview with Saverio where he explains it in more detail. This interview will be coming up in a future edition of the Bluebox Podcast, run by two of our VOIPSA Chairs, Dan York and Jonathan Zar.

VoIP Phreaking in the Desert

On the Infoworld Zero Day Security page, Garza talks a little about the VoIP Phreaking session at the Black Hat conference, which is on right now in Las Vegas.  I’m looking forward to the promised podcast with The Grugg, who led that class.

On the Black Hat website is an archive of presentations from previous conferences, and the ones from the current conference should pop-up there in the coming weeks. 

Newport Wobbles

News broke last week about Session Border Controller manufacturer Newport Networks, which has run into cash-flow problems waiting for deals to close.  Newport Networks was started by serial entrepreneur Sir Terry Matthews, reportedly Wales’s first billionaire, who also founded Newbridge (now part of Alcatel) and Mitel.

Last year Newport were lined up to supply their 1460 Session Border Controller to troubled equipment supplier Marconi.  Marconi themselves failed to become prime NGN suppliers to British Telecom, which ultimately resulted in the failure of the company.  The rump of Marconi has now been absorbed into Ericsson.

Newport have announced layoffs, as reported at ZDNet and in the UK Guardian Newspaper, in an attempt to reduce cash burn while waiting for the business to arrive.  It’s ironic with CALEA in the headlines and telcos rolling out NGNs that a provider of the enabling technology should have run onto the rocks.  Let’s hope the Newport investors can keep their nerve. 

Skype to Address User-Identification Concerns

In an interestingly eerie parallel to a discussion that has recently cropped up on the VoIPSec forum regarding peer-entity authentication vs. data-origin authentication, Skype announced yesterday that it intends to address the issue of user-identification within their VoIP service.

Part of Skype’s “wish list” for further expansion into the business market is to enhance username authentication for business customers, the voice over Internet Protocol company said Wednesday.

Skype’s system currently automatically authenticates users itself, based on certificates from it’s own encrypted Public Key Infrastructure (PKI). Because it does this automatically and transparently to the user, the users themselves have no way of authenticating the identity of the person they are communicating with.

“Skype is a public key infrastructure, which means nothing if you don’t know who you are identifying at the other end,” Sauer said.

You can read more detail at

Skype security

RECON (Reverse Engineering Conference) was recently held from June 16-18 in Montreal. One of the presentations involved some in-depth Skype reverse engineering and analysis. The slides for the presentation are available in pdf format for part1 and part2. Among other things, the talk covered Skype’s crypto scheme, easter eggs, and general traffic analysis. Worth a read.

Researchers seek to save VoIP from security threats

An article from ComputerWorld discusses a grant that the NSF has earmarked for the research of VoIP security threats:

The National Science Foundation says it has issued US$600,000 to the University of North Texas to spearhead development of a multi-university test bed to study VoIP security. Other participants are Columbia University, Purdue University and the University of California-Davis. VoIP spam, denials of service, emergency services and quality of service will be among the areas targeted for research during the three-year project. The research will also look at vulnerabilities that emerge from the integration of VoIP and legacy networks.

The group of schools plans to disseminate its findings widely to technology developers, academia and others involved in network convergence.

Ram Dantu from the Univeristy of North Texas is leading the charge and is also a member of VOIPSA’s Technical Advisory Board, as are several of the other researchers involved in this grant. Ram has been intrumental is driving the state of VoIP security not only through his own research and professional career, but by organizing industry workshops on VoIP security.

I expect the results from their efforts to be sobering, hopefully helping vendors and providers to enhance the security of their solutions and offerings.