VoIP Eavesdropping: UCSniff (I)

After a long time without writing because of different reasons I´m going to begin a group of articles trying to cover different type of attacks against any of the components of a common VoIP (Voice Over Internet Protocol) infrastructure and how to stop them. If you are beginning in this world of VoIP I recommend you to read Building Telephony Systems with OpenSIPS 1.6 where the authors go through basic theoretical and practical skills needed to implement a complete system.

This time, I will start with VoIP Eavesdropping attack, as the name suggest it consists on listen a conversation without speakers consent. This attack existed in the traditional telephony systems and nowadays is also possible against VoIP ones (and other protocols too, in example bluetooth).

As you can imagine we are in front of a classic sniffing attack so, first of all, we need to gain access. Any of the techniques you know are ok, moreover, there are another specific ways for this kind of systems of getting the .pcap file we are looking for. For example, some phones have a "feature" which allows saving a .pcap with all traffic passing over its interfaces and more of them have vulnerabilities in their web control panel, so it could be possible to access to this profitable file :). But this is not the topic of this article despite of being an interesting one too, so I hope take it up again another day.

Now we have the capture, then we need a tool able to understand SIP (Session Initiation Protocol) and RTP (Real-time Transport Protocol), among others. The most used option is Whireshark, but it doesn´t support H.264 video codec so we can´t eavesdrop video conversations, in this case we should call it IP Video Eavesdropping not VoIP Eavesdropping. I found this video where we can see an example of this:

I like Wireshark for studying specific situations but, anyway, we need something more automatic for pentesting tests in order to be capable of reconstruct and synchronize conversations correctly. I usually use Xplico for this kind of things but, for the moment, SIP, SDP and RTP protocol are not fully supported as we can see in the website:

Figure: Xplico supported protocols state 

Today we will use UCSniff, a tool which allows to rapidly test for the threat of unauthorized VoIP and Video Eavesdropping. I paste here some features:
- Audio Eavesdropping
- Video Eavesdropping (creates H.264 format file)
- Realtime Audio Monitor
- GUI Support
- Realtime Video Monitor
- Creates an avi file and muxes audio and video
- Creates a wav file and muxes both forward and reverse audio

For this POC (Proof Of Concept) I will use two virtual machines, one with BT (Backtrack) 5 and Zoiper Classic as client (I had problems running Ekiga on BT5) and another with a Debian Squeeze with a basic installation of Asterisk. It is not a very real environment but it´s enough for this POC, so we don´t need to do MitM (Main in the Middle). I’m sure if you are reading this you know how to gain access with you favorite sniffer or UCSniff ;).

OK, first we need to download the latest version of UCSniff (here) and to install dependencies to compile it on BT5 with GUI (Graphical User Interface) and realtime video monitor:

apt-get install build-essential zlib1g-dev liblzo2-dev libpcap0.8-dev libnet1-dev libasound2-dev libbz2-dev libncurses5-dev apt-get install libx11-dev libxext-dev libfreetype6-dev

NOTE: VLC version and development libraries included in BT5 broke the compilation, so we have to install it directly from VLC repositories before:

add-apt-repository ppa:lucid-bleed/ppa
apt-get update
apt-get install vlc libvlc-dev

Now, go in ucsniff-3.0 folder and compile it:

./configure --enable-libvlc --enable-gui
make install

We are ready for run it (graphical interface) for the first time:

ucsniff -G

Figure: UCSniff general view

Yes, it´s not too sexy, above all these evil buttons! xD. For this test we have to select Monitor Mode and Start Sniffing like in the picture and the sniffer will start to capture. Next step is making a call, I will call myself (yes, it´s possible! you should try it :D).

Figure: Calling myself

After accepting the incoming Output Console will log it as in the next two pictures (second took after hang up from one side).

Figure: Logging calls

Well done!, we can see the conversation was captured, there are two calls instead of only one because of virtual machine interface really is mapped to another, but it works, one of this two .wav will be empty and the other will contain saved conversation. I think it´s enough for the first day. Next article we will review all the outputs produced by the sniffer and we are going to deep a bit more in this attack. At the moment, I recommend you visiting the site of the tool where you can learn more about it and view examples using the GUI with MitM and Video Eavesdropping: http://ucsniff.sourceforge.net/guiusage.html

Figure: UCSniff Video Eavesdropping

Jesús Pérez