Back in April 2020 a Citizenlab reported on Zoom’s rather weak encryption and stated that Zoom uses the SILK codec for audio. Sadly, the article did not contain the raw data to validate that and let me look at it further. Thankfully Natalie Silvanovich from Googles Project Zero helped me out using the Frida tracing tool and provided a short dump of some raw SILK frames. Analysis of this inspired me to take a look at how WebRTC handles audio. In terms of perception, audio quality is much more critical for the perceived quality of a call as we tend to notice even small glitches. Mere ten seconds of this audio analysis were enough to set me off on quite an adventure investigating possible improvements to the audio quality provided by WebRTC. ...
webrtcH4cKS: ~ True End-to-End Encryption with WebRTC Insertable Streams
A couple of weeks ago, the Chrome team announced an interesting Intent to Experiment on the blink-dev list about an API to do some custom processing on top of WebRTC. The intent comes with an explainer document written by Harald Alvestrand which shows the basic API usage. As I mentioned in my last post, this is the sort of thing that maybe able to help add End-to-End Encryption (e2ee) in middlebox scenarios to WebRTC.
I had been watching the implementation progress with quite some interest when former webrtcHacks guest author Emil Ivov of jitsi.org reached out to discuss collaborating on exploring what this API is capable of. Specifically, we wanted to see if WebRTC Insertable Streams could solve the problem of end-to-end encryption for middlebox devices outside of the user’s control like Selective Forwarding Units (SFUs) used for media routing. ...
Time for another opinionated post. This time on… end-to-end encryption (e2ee). Zoom apparently claims it supports e2ee while it can not satisfy that promise. Is WebRTC any better?
Zoom does not have End to End Encryption
Let’s get to the bottom of things fast: Boo Zoom!
I reviewed how Zoom’s implements their web client last year.
I’m not really surprised of their general lack of e2ee given that their web client did not provide any encryption on top of TLS or WebRTC’s DataChannel. For reasons we will discuss below, this means they weren’t doing any obvious e2ee there. ...
webrtcH4cKS: ~ Not a Guide to SDP Munging
SDP has been a frequent topic, both here on webrtcHacks as well as in the discussion about the standard itself. Modifying the SDP in arcane ways is referred to as SDP munging. This post gives an introduction into what SDP munging is, why its done and why it should not be done. This is not a guide to SDP munging.
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webrtcH4cKS: ~ Is everyone switching to Unified Plan?
Editor’s Note: This post was originally published on October 23, 2018. Zoom recently started using WebRTC’s DataChannels so we have added some new details at the end in the DataChannels section.
Zoom has a web client that allows a participant to join meetings without downloading their app. Chris Koehncke was excited to see how this worked (watch him at the upcoming KrankyGeek event!) so we gave it a try. It worked, removing the download barrier. The quality was acceptable and we had a good chat for half an hour. ...
webrtcH4cKS: ~ The WhatsApp RTCP exploit – what might have happened?
As you may have heard, Whatsapp discovered a security issue in their client which was actively exploited in the wild. The exploit did not require the target to pick up the call which is really scary.
Since there are not many facts to go on, lets do some tea reading…
The security advisory issued by Facebook says
A buffer overflow vulnerability in WhatsApp VOIP stack allowed remote code execution via specially crafted series of SRTCP packets sent to a target phone number.
This is not much detail, investigations are probably still ongoing. I would very much like to hear a post-mortem how WhatsApp detected the abuse. ...
webrtcH4cKS: ~ Finding the Warts in WebAssembly+WebRTC
A while ago we looked at how Zoom was avoiding WebRTC by using WebAssembly to ship their own audio and video codecs instead of using the ones built into the browser’s WebRTC. I found an interesting branch in Google’s main (and sadly mostly abandoned) WebRTC sample application apprtc this past January. The branch is named wartc… a name which is going to stick as warts!
The repo contains a number of experiments related to compiling the webrtc.org library as WebAssembly and evaluating the performance. From the rapid timeline, this looks to have been a hackathon project. ...
webrtcH4cKS: ~ First steps with QUIC DataChannels
QUIC-based DataChannels are being considered as an alternative to the current SCTP-based transport. The WebRTC folks at Google are experimenting with it:
Looking for feedback: QUIC based RTCQuicTransport and RTCIceTransport API's are available as origin trial in Chrome 73 for experimentation.https://t.co/KVVEVmggms
— WebRTC project (@webrtc) February 1, 2019
Let’s test this out. We’ll do a simple single-page example similar to the WebRTC datachannel sample that transfers text. It offers a complete working example without involving signaling servers and also allows comparing the approach to WebRTC DataChannels more easily. ...
webrtcH4cKS: ~ Let’s get better at fuzzing in 2019 – here’s how
Fuzzing is a Quality Assurance and security testing technique that provides unexpected, often random data to a program input to try to break it. Natalie Silvanovich from Google’s Project Zero team has had quite some fun fuzzing various different RTP implementations recently.
She found vulnerabilities in:
- WebRTC — mostly issues in the RTP payload
- Facetime – a few out-of-bounds, stack corruption, and heap corruption issues
- Whatsapp and what didn’t work
In a nutshell, she found a bunch of vulnerabilities just by throwing unexpected input at parsers. The range of applications which were vulnerable to this shows that the WebRTC/VoIP community does not yet have a process for doing this work ourselves. Meanwhile, the WebRTC folks at Google will have to improve their processes as well. ...