[rollcat]

> How is knowing the local IP a security issue?

It's a privacy issue. You can use it to fingerprint a user, local IP will give you quite many bits of entropy. <https://coveryourtracks.eff.org/>

Honestly I'm not even sure if I'm surprised, but it's 2022 and we've been having this problem basically since the day WebRTC was introduced. At this point, if you care about privacy, you should probably put it in the same bag as third-party cookies and just block it entirely.

[londons_explore]

It's because if you don't leak the local IP, then webRTC calls will typically fail between people on the same LAN. And, if they don't fail, then they will usually have to go via a TURN server on the internet adding a lot of latency.

It's a privacy/functionality tradeoff. But most people consider not being able to videocall or do online gaming with someone in the same building to not be acceptable.

[codedokode]

I don't think that there are many people using WebRTC especially within the same LAN, but fingerprinting is used by almost every commercial site. So I can assume that this "feature" was used in 99.99% cases for fingerprinting.

This shows how browser developers race to push new features without proper estimation of privacy concerns.

Luckily this was somewhat fixed by using randomized Apple mDNS names instead of IPs. But as a result the browser has to support Apple DNS protocol which can potentially increase attack surface.

I would prefer to disable this feature completely by default and let the minority who needs it enable it via settings.

[rollcat]

> But as a result the browser has to support Apple DNS protocol which can potentially increase attack surface.

The "Apple" DNS protocol is standard DNS, over a multicast IP address, on port 5353. You can literally use plain old dig to perform mDNS lookups:

    $ dig @224.0.0.251 -p 5353 +short hello.local

    192.168.123.45

If DNS lookups considerably increase your attack surface, something is very, very wrong with your architecture.

[webrtcdev1]

> literally

The DNS names WebRTC generates for this purpose are random, and known only to the signaling participants.

[wbl]

I remember old BIND versions

[Sean-Der]

I see a lot of WebRTC usage just in the LAN. WebRTC sees a lot of usage outside of conferencing!

* Controlling Robots (formant.io)

* Security Cameras

* File Sharing

* Game Streaming/VNC

I keep a list of interesting open source WebRTC projects at https://github.com/pion/awesome-pion

[nemothekid]

>I don't think that there are many people using WebRTC especially within the same LAN

Zoom/Teams with people in the same office? That seems like a rather large user base

Almost all of the “sales/demo/cross company” video calls I’ve been on have been in this bucket

[cma]

> Almost all of the “sales/demo/cross company” video calls I’ve been on have been in this bucket

My understanding is Zoom only supports P2P for two person calls.

I can't quite tell from this answer if it is the default or not, but it sounds like it has to be manually enabled:

> Account owners and admins can enable one-on-one meetings to have data routed between two participants (peer-to-peer), rather than going through the cloud or server. Enabling this may improve the quality and connection of one-on-one meetings (depending on how your network prioritizes traffic) by directly sending video and audio between both parties.

https://support.zoom.us/hc/en-us/articles/360061410851-Enabl...

[bawolff]

> This shows how browser developers race to push new features without proper estimation of privacy concerns.

Settling on a different trade-off then you would like is not the same thing as doing it without consideration.

[coldtea]

In this case, it is blatant disregard.

[helloooooooo]

Corporate networks…

[easrng]

They use MDNS hostnames to keep WebRTC working on LANs without leaking the IP itself, this was just an extra leak they didn't catch.

[ZiiS]

Are you sure? I bet most people have never even tried to do that.

[Semaphor]

Well, the big non-adtech browser is not vulnerable, so there’s that.

[amenghra]

https://bugzilla.mozilla.org/show_bug.cgi?id=959893 is a fun read... Firefox used to also leak the internal IP circa 2015.

[codedokode]

Yes it is interesting how developers race to push new features allowing deanonimization of VPN users and better fingerprinting.

There is also WebGL whose main purpose is to provide user's videocard model to advertising companies and governemnt institutions.

[lxgr]

> just block [WebRTC] entirely

I think an opt-in permission seems like the way to go, like the one we already have for microphone/camera permissions, and possibly just merged with these (i.e. grant WebRTC permissions together with A/V permissions).

There are quite a few interesting non-A/V WebRTC applications around – these could be handled via an explicit prompt, similarly to how newer iOS versions handle local network permissions.

[MomoXenosaga]

If memory serves Ublock origin does just that.

[Semaphor]

Not anymore on Desktop: https://github.com/gorhill/uBlock/wiki/Prevent-WebRTC-from-l...

[geocar]

> It's a privacy issue. You can use it to fingerprint a user, local IP will give you quite many bits of entropy. <https://coveryourtracks.eff.org/>

I don't buy it: You have to block IPv6 as well, and that's becoming harder to do.

If the user is trying to protect their "privacy" from their ISP by using a VPN (for example), and are attempting to prevent the application-level leak of providing a list of all the local interfaces, they really need to configure their system to restrict e.g. their web browsers and other sensitive tools to those specific interfaces, e.g.

https://askubuntu.com/questions/1313755/forcing-chrome-brows...

This should be easier, like maybe a button in the VPN software.