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Adventures in Video Conferencing Part 4: What Didn't Work Out with WhatsApp

Posted by Natalie Silvanovich, Project Zero
Not every attempt to find bugs is successful. When looking at WhatsApp, we spent a lot of time reviewing call signalling hoping to find a remote, interaction-less vulnerability. No such bugs were found. We are sharing our work with the hopes of saving other researchers the time it took to go down this very long road. Or maybe it will give others ideas for vulnerabilities we didn’t find.
As discussed in Part 1, signalling is the process through which video conferencing peers initiate a call. Usually, at least part of signalling occurs before the receiving peer answers the call. This means that if there is a vulnerability in the code that processes incoming signals before the call is answered, it does not require any user interaction.
WhatsApp implements signalling using a series of WhatsApp messages. Opening libwhatsapp.so in IDA, there are several native calls that handle incoming signalling messages.
Java_com_whatsapp_voipcalling_Voip_nativeHan…

Adventures in Video Conferencing Part 3: The Even Wilder World of WhatsApp

Posted by Natalie Silvanovich, Project Zero
WhatsApp is another application that supports video conferencing that does not use WebRTC as its core implementation. Instead, it uses PJSIP, which contains some WebRTC code, but also contains a substantial amount of other code, and predates the WebRTC project. I fuzzed this implementation to see if it had similar results to WebRTC and FaceTime. Fuzzing Set-upPJSIP is open source, so it was easy to identify the PJSIP code in the Android WhatsApp binary (libwhatsapp.so). Since PJSIP uses the open source library libsrtp, I started off by opening the binary in IDA and searching for the string srtp_protect, the name of the function libsrtp uses for encryption. This led to a log entry emitted by a function that looked like srtp_protect. There was only one function in the binary that called this function, and called memcpy soon before the call. Some log entries before the call contained the file name srtp_transport.c, which exists in the PJSIP repos…

Adventures in Video Conferencing Part 2: Fun with FaceTime

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Posted by Natalie Silvanovich, Project Zero
FaceTime is Apple’s video conferencing application for iOS and Mac. It is closed source, and does not appear to use any third-party libraries for its core functionality. I wondered whether fuzzing the contents of FaceTime’s audio and video streams would lead to similar results as WebRTC. Fuzzing Set-up
Philipp Hancke performed an excellent analysis of FaceTime’s architecture in 2015. It is similar to WebRTC, in that it exchanges signalling information in SDP format and then uses RTP for audio and video streams. Looking at the FaceTime implementation on a Mac, it seemed the bulk of the calling functionality of FaceTime is in a daemon called avconferenced. Opening up the binary that supports its functionality, AVConference in IDA, it contains a function called SRTPEncryptData. This function then calls CCCryptorUpdate, which appeared to encrypt RTP packets below the header.
To do a quick test of whether fuzzing was likely to be effective, I hooked …

Adventures in Video Conferencing Part 1: The Wild World of WebRTC

Posted by Natalie Silvanovich, Project Zero
Over the past five years, video conferencing support in websites and applications has exploded. Facebook, WhatsApp, FaceTime and Signal are just a few of the many ways that users can make audio and video calls across networks. While a lot of research has been done into the cryptographic and privacy properties of video conferencing, there is limited information available about the attack surface of these platforms and their susceptibility to vulnerabilities. We reviewed the three most widely-used video conferencing implementations. In this series of blog posts, we describe what we found.
This part will discuss our analysis of WebRTC. Part 2 will cover our analysis of FaceTime. Part 3 will discuss how we fuzzed WhatsApp. Part 4 will describe some attacks against WhatsApp that didn’t work out. And finally, Part 5 will discuss the future of video conferencing and steps that  developers can take to improve the security of their implementation. Typi…