[rtcweb] Fwd: [discuss-webrtc] PSA: Private IP addresses exposed by WebRTC changing to mDNS hostnames

[Justin Uberti <[e-mail]>]

FYI, empirical results of deploying mDNS at scale. TL;DR: downside is low,
~2% impact to data channel connection rate between Chrome instances,
somewhat higher when connecting to non-Chrome, likely due to issues
handling mDNS candidates, which should be temporary.

In the absence of any showstopper feedback, planning to roll this out fully
later this month.

---------- Forwarded message ---------
From: 'Qingsi Wang' via discuss-webrtc <[e-mail]>
Date: Tue, Aug 13, 2019 at 2:33 PM
Subject: [discuss-webrtc] PSA: Private IP addresses exposed by WebRTC
changing to mDNS hostnames
To: discuss-webrtc <[e-mail]>


Summary

WebRTC currently lets web applications discover private IP addresses to
enable direct connectivity between hosts on a local network. While private
IP addresses do not uniquely identify browser users, they may still be used
for tracking purposes. To prevent this misuse, private IP addresses
returned by RTCPeerConnection will now be masked with mDNS hostnames in
certain situations. While this change should be transparent to most WebRTC
applications, some developers may need to update their client and backend
services.

This change is currently enabled for 50% of Chrome users, and is expected
to fully roll out in August 2019 as part of the Chrome 76 release. WebRTC
services can verify whether their services are affected by setting the
following flag in Chrome 73 or later:
chrome://flags/#enable-webrtc-hide-local-ips-with-mdns

Why are we doing this?

We have observed a trend of web sites using WebRTC specifically to obtain
private IP addresses, presumably for tracking purposes. Accordingly, we
have collaborated with other browser vendors to address this problem by
using mDNS hostnames instead of private IP addresses in WebRTC, as
described in this pending IETF spec
<https://tools.ietf.org/html/draft-ietf-rtcweb-mdns-ice-candidates-03>. We
have also experimentally verified the efficacy of the mDNS technique,
following the initial announcement of this feature in January
<https://groups.google.com/forum/#!msg/discuss-webrtc/4Yggl6ZzqZk/nV24XkXXAQAJ>
.

Impact on applications

When the feature is active, private IP addresses in ICE host candidates
will be replaced by an mDNS hostname, e.g.,
1f4712db-ea17-4bcf-a596-105139dfd8bf.local. Currently, this feature is
active for all sites except those that have getUserMedia permissions, which
are presumed to have a higher degree of user trust.

WebRTC services that do not support addresses in the above format may be
impacted, causing sessions to fail or use a less direct connection path. WebRTC
services may be especially affected if they parse out addresses from
RTCSessionDescription or RTCIceCandidate objects and assume those addresses
are IP addresses, or have server components that do the same. In
particular, older versions of the libnice library, used by some
applications, do not parse such addresses properly.

Impact on connectivity

mDNS does not work in all situations; on some networks, mDNS may be
disabled, or an endpoint may be too many hops away to resolve an mDNS
hostname. In these cases, fallback to STUN will be required, and this may
sometimes fail; as such, some amount of impact on connection success rate
is to be expected.



>From a broad analysis of peer-to-peer connections in the experimental
deployment, the overall impact of mDNS on connectivity is modest, a 2%
(relative) reduction in connection rate when mDNS was used by Chrome on
both sides. In this population, the percentage of successful connections
that used STUN on one side or the other increased from 94% to 97%, with a
corresponding decrease in host-to-host connections. We believe the
connectivity impact stems primarily from connections that previously worked
host-to-host, but do not work with mDNS, and cannot fall back to STUN due
to lack of hairpin support in the NAT.



Somewhat surprisingly, for connections between Chrome and non-mDNS
endpoints, we observed a larger impact, roughly 3% (relative) reduction in
connection rate when the remote side supplied private IPs and 7% (relative)
when the remote side supplied only public IPs. While mDNS should have zero
impact in these cases, we believe this is explained by problems triggered
by mDNS in third-party ICE stacks, including the aforementioned issues
regarding parsing mDNS candidates as well as issues discovering
peer-reflexive candidates from ICE connectivity checks.



Given the success of the mDNS technique in combating tracking via private
IP addresses, we believe this small impact on connection rate is an
acceptable tradeoff. We will continue to investigate improvements to this
technique to further minimize the downsides.

General recommendations

Improvements in Chrome are frequently rolled out as experiments and deploy
first in Chrome Canary and the pre-stable Dev and Beta versions. Important
experiments are also announced via email at the start of the rollout. We
highly recommend WebRTC developers to:

   -

   Join blink-dev
   <https://groups.google.com/a/chromium.org/forum/#!forum/blink-dev> and
   discuss-webrtc <https://groups.google.com/forum/#!forum/discuss-webrtc>
   to follow PSAs and other important announcements
   -

   Systematically test in Chrome Canary
   <https://www.google.com/chrome/canary/> to see how your application
   behaves with upcoming Chrome changes
   -

   Provide feedback on the relevant bugs/forum threads

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