Fwd: Intent to unship: TLS 1.0 and TLS 1.1

Patrick Cloke patrick at cloke.us
Thu Sep 12 12:40:16 UTC 2019

I'm curious what effect this will have on Thunderbird. Do we have any 
idea what percentage of SMTP/IMAP/POP servers are using these versions 
of TLS?


-------- Forwarded Message --------
Subject: Intent to unship: TLS 1.0 and TLS 1.1
Date: Thu, 12 Sep 2019 14:03:39 +1000
From: Martin Thomson <mt at mozilla.com>
To: dev-platform <dev-platform at lists.mozilla.org>
Newsgroups: mozilla.dev.platform
<CAPLxc=UoDyskquLxob5fMTwL8NMtOeFQSWMsQE5kh-2KAZor+A at mail.gmail.com>

(We’ve had a couple of blog postings about this [1][2], but this list
hasn’t received an explicit intent notice.  Now that we’re starting to make
changes, it seems like a good time to correct that oversight.)

TLS 1.0 and 1.1 are old.  They are also broken in myriad subtle ways. [3]
explains in more detail.

Disabling TLS 1.0 and 1.1 is part of an agreement we have negotiated with
other browsers.  We have agreed with Apple, Google, and Microsoft to
disable this version in March 2020. Safari Tech Preview has already made
this change [4].

We have been measuring the impact of this change at [5], which shows steady
progress from sites.  Telemetry shows that TLS 1.0 usage is much higher
than we would ordinarily tolerate for this sort of deprecation [6], but we
are confident in the commitment that other browsers have made. The trend in
both measurements supports the view that the number of sites that will be
affected is reducing steadily [7].

The first step on this path landed in Firefox 68.  That was to show a
warning in developer tools.

The step we’re about to take disables TLS 1.0 and 1.1 in Nightly.  The plan
is to do that in the Firefox 71 cycle. Bug 1579270 tracks this change.

After that we plan to start progressively disabling TLS 1.0 and 1.1 in Beta
as that Firefox 71 and subsequent versions are deployed.  This will likely
start by making the change for a very small percentage of people using
Beta, then increasing as we gather feedback. The idea is to have all of
Beta switched over ahead of March.

Finally, we will disable TLS 1.0 and 1.1 for all people using the Release
channel of Firefox in March 2020.  Exact plans for how and when this will
happen are not yet settled.

Bug 1579285 is tracking updates to the SSL_ERROR_UNSUPPORTED_VERSION error
page that we expect will get more use.  That page currently offers to reset
preferences. We are considering offer the option to re-enable old TLS
versions.  However, we would remove that capability in a build that will go
to Release in or shortly after March.

Independent of this, WebRTC uses DTLS, which has a similar story. DTLS 1.0
is effectively TLS 1.1.  However, WebRTC has higher DTLS 1.0 usage rates
[8]. The WebRTC team are considering disabling support for DTLS 1.0 at the
same time, but might defer that decision.

This is a potentially disruptive change, but we believe that this is good
for the security and stability of the web.



[2] https://hacks.mozilla.org/2019/05/tls-1-0-and-1-1-removal-update/

[3] https://tools.ietf.org/html/draft-ietf-tls-oldversions-deprecate-05


[5] The second graph at
http://tlscanary-plot-8e95d89854d73f4d.elb.us-west-2.amazonaws.com/ ;
ignore the jump prior to May, that’s the result of a methodology change to
switch the list of sites that are scanned.

[6] https://sql.telemetry.mozilla.org/queries/64283#164115 shows values for
Release, which puts TLS 1.0 between 0.46% and 0.68% depending on the time
of week.  TLS 1.1 is virtually non-existent at 0.02%, we could have removed
that already if it weren’t for the fact that this isn’t how TLS version
negotiation works.

[7] ibid. In October last year, TLS 1.0 was in the range of 0.65% to 1%.
[8] https://mzl.la/2ZIHK55

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