AW: RFC 9525 obsoletes commonName check

[Viktor Dukhovni]

On Sat, Nov 18, 2023 at 11:21:16AM +0100, Georg Höllrigl wrote:

> 
>    CN was deprecated in May 2000 - RFC 2818:
>    If a subjectAltName extension of type dNSName is present, that MUST
>    be used as the identity. Otherwise, the (most specific) Common Name
>    field in the Subject field of the certificate MUST be used. Although
>    the use of the Common Name is existing practice, it is deprecated and
>    Certification Authorities are encouraged to use the dNSName instead.

Note the **If**, and the mandatory fallback to CN.  So at that time it
was superceded by SAN, but not yet effectively deprecated.

> In 2017 Chromium enforced use of SAN, and to my knowledge the other browsers followed:
> 
> https://chromestatus.com/feature/4981025180483584
> https://textslashplain.com/2017/03/10/chrome-deprecates-subject-cn-matching/

These actually removed support for CN-ID, and it is great that the
browsers are in a position to do that.

OpenSSL, however, is used in all kinds of intramural legacy systems, and
backwards-compatibility is an important consideration.

If we stop accepting CN-ID fallback by default, barring evidence that
"nobody" still relies on CN-ID, OpenSSL should at least initially (in
the first LTS release that changes the default) provide a flag that
reënables the fallback, and only remove support in a subsequent release,
giving users ample time to make the transition.

What is the aim of this thread, is it a question, feature request, bug
report, or preliminary discussion?

-- 
    Viktor.