Technology

webrtcH4cKS: ~ The WhatsApp RTCP exploit – what might have happened?

Posted by Philipp Hancke on May 17, 2019
Posted in: Reverse-Engineering, Technology.
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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. ...

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webrtcH4cKS: ~ Finding the Warts in WebAssembly+WebRTC

Posted by Philipp Hancke on April 11, 2019
Posted in: Reverse-Engineering, Technology.
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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. ...

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webrtcH4cKS: ~ First steps with QUIC DataChannels

Posted by Philipp Hancke on February 11, 2019
Posted in: Guide, Technology.
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QUIC-based DataChannels are being considered as an alternative to the current SCTP-based transport. The WebRTC folks at Google are experimenting  with it:

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. ...

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webrtcH4cKS: ~ What I learned about H.264 for WebRTC video (Tim Panton)

Posted by Tim Panton on January 29, 2019
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It has been a few years since the WebRTC codec wars ended in a detente. H.264 has been around for more than 15 years so it is easy to gloss over the the many intricacies that make it work.

Reknown hackathon star, live-coder, and |pipe| CTO Tim Panton was working on a drone project where he needed a light-weight H.264 stack for WebRTC, so he decided to build one. This is certainly not an exercise I would recommend for most, but Tim shows it can be an enlightening experience if not an easy one. In this post, Tim walks us through his step-by-step discovery as he just tries to get video to work. Check it out for an enjoyable alternative to reading through RFCs specs for an intro on H.264! ...

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webrtcH4cKS: ~ Improving Scale and Media Quality with Cascading SFUs (Boris Grozev)

Posted by Boris Grozev on November 12, 2018
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Deploying media servers for WebRTC has two major challenges, scaling beyond a single server as well as optimizing the media latency for all users in the conference. While simple sharding approaches like “send all users in conference X to server Y” are easy to scale horizontally, they are far from optimal in terms of the media latency which is a key factor in the user experience. Distributing a conference to a network of servers located close to the users and interconnected with each other on a reliable backbone promises a solution to both problems at the same time. Boris Grozev from the Jitsi team describes the cascading SFU problem in-depth and shows their approach as well as some of the challenges they ran into. ...

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webrtcH4cKS: ~ Breaking Point: WebRTC SFU Load Testing (Alex Gouaillard)

Posted by Alex Gouaillard on October 18, 2018
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If you plan to have multiple participants in your WebRTC calls then you will probably end up using a Selective Forwarding Unit (SFU).  Capacity planning for SFU’s can be difficult – there are estimates to be made for where they should be placed, how much bandwidth they will consume, and what kind of servers you need.

To help network architects and WebRTC engineers make some of these decisions, webrtcHacks contributor Dr. Alex Gouaillard and his team at CoSMo Software put together a load test suite to measure load vs. video quality. They published their results for all of the major open source WebRTC SFU’s. This suite based is the Karoshi Interoperability Testing Engine (KITE) Google funded and uses on webrtc.org to show interoperability status. The CoSMo team also developed a machine learning based video quality assessment framework optimized for real time communications scenarios. ...

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webrtcH4cKS: ~ Suspending Simulcast Streams for Savvy Streamlining (Brian Baldino)

Posted by Brian Baldino on August 6, 2018
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If you’re new to WebRTC, Jitsi was the first open source Selective Forwarding Unit (SFU) and continues to be one of the most popular WebRTC platforms. They were in the news last week because their parent group inside Atlassian was sold off to Slack but the team clarified this does not have any impact on the Jitsi team. Helping to show they are still chugging along, they released a new feature they wanted to talk about – off-stage layer suspension. This is a technique for minimizing bandwidth and CPU consumption when using simulcast. Simulcast is a common technique used in multi-party video scenarios. See Oscar Divorra’s post on this topic and that Fippo post just last week for more on that. Even if you are not implementing a  simulcast, this is a good post for understanding how to control bandwidth and to see some follow-along reverse-engineering on how Google does things in its Hangouts upgrade called Meet. ...

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webrtcH4cKS: ~ Chrome Screensharing Blues – preparing for getDisplayMedia

Posted by Philipp Hancke on June 14, 2018
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What happens when you screen share on a computer that's already sharing your screen

The Chrome Webstore has decided to stop allowing inline installation for Chrome extensions. This has quite an impact on WebRTC applications since screensharing in Chrome currently requires an extension. Will the getDisplayMedia API come to the rescue?

Screensharing in Chrome

When screensharing was introduced in Chrome 33, it required implementation via an extension as a way to address the security concerns. This was better than the previous experience of putting this capability behind a flag which lead to sites asking their users to change that flag… that got those sites an official yikes. ...

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webrtcH4cKS: ~ Autoplay restrictions and WebRTC (Dag-Inge Aas)

Posted by Dag-Inge Aas on May 7, 2018
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One of the great things about WebRTC is that it is built right into the web platform. The web platform is generally great for WebRTC, but occasionally it can cause huge headaches when specific WebRTC needs do not exactly align with more general browser usage requirements. The latest example of this is has to do with the autoplay of media where sound(s) suddenly went missing for many users. Former webrtcHacks guest author Dag-Inge Aas has been dealing with this first hand. See below for his write-up on browser expectations around the playback of media, the recent Chrome 66+ changes, and some tips and tricks for working around these issues. ...

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webrtcH4cKS: ~ So your VPN is leaking because of Chrome’s WebRTC…

Posted by Philipp Hancke on April 2, 2018
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Brussel’s Mannneken Pis. Original photo by Flickr user Francisco Antunes (CC BY 2.0)

We have covered the “WebRTC is leaking your IP address” topic a few times, like when I reported what the NY Times was doing and in my WebRTC-Notifier. Periodically this topic comes up now and again in the blogosphere, generally with great shock and horror. This happened again recently, so here is an updated look into this alleged issue.

The recent blog post titled VPN Leak by voidsec highlighting how 19 out of more than 100 VPN services tested “leak” IP addresses via WebRTC is a quite interesting read. Some of the details about WebRTC are not quite correct the results are interesting nonetheless. At is core this is someone who sat down to test a long list of services and their behaviour, one by one. This is not the most exciting research task, but exhaustive studies like this often find something interesting. ...

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