[openssl-project] FYI: [postfix & TLS1.3 problems]

Viktor Dukhovni openssl-users at dukhovni.org
Thu Oct 11 17:18:03 UTC 2018

Apparently, some SMTP clients set fallback_scsv when doing TLS 1.2
with Postfix servers using OpenSSL 1.1.1.  Not yet clear whether
they tried TLS 1.3 first and failed, or just sent the SCSV out of
the blue...

See attached.  If this is a common problem, it might be useful to
have a control that tolerates "downgrade" to TLS 1.2, without
disabling TLS 1.3 support.  In many cases, and especially opportunitistic
security, where STARTTLS can be stripped by an MiTM entirely, so
we often can't even prevent downgrades to cleartext, TLS 1.2 is
quite good enough.

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