nginx on current implicitly enables TLS 1.3 (with only "ssl_protocols TLSv1.2; " in nginx.conf config)

[Andreas Bartelt]

Hi,

I think I've found a bug in current (snapshot from today) with regard to 
nginx from ports, LibreSSL and TLS 1.3 which is implicitly enabled even 
if configured otherwise.

From nginx.conf:
        ssl_protocols TLSv1.2;
Expected behavior: only enables TLS 1.2
Observed behavior on current: enables TLS 1.2 and TLS 1.3

See also my bug report at nginx mailing list: 
https://marc.info/?t=160666207900003&r=1&w=2

Is there something wrong or missing on the LibreSSL side which triggers 
this bug?

Best regards
Andreas