ssl_tls13_server does not respect config's min_tls_version value

[alluettiv]

Summary

In hybrid mode (mbedTLS compiled with TLS 1.2 and 1.3 support), ssl_tls13_server uses mbedtls_ssl_config.max_tls_version to setup initial TLS version. Then, during a handshake, if a client connects using TLS1.2, ssl_tls13_server downgrades protocol to TLS1.2 regardless of mbedtls_ssl_config.min_tls_version value.

System information

Mbed TLS version 3.5.0:
Operating system and version: Any
Configuration: mbedtls_config.h.txt

Expected behavior

ssl_tls13_server should reject TLS1.2 connections if it was configured with mbedtls_ssl_config.min_tls_version >=MBEDTLS_SSL_VERSION_TLS1_3 at runtime via mbedtls_ssl_conf_min_tls_version(&cfg, MBEDTLS_SSL_VERSION_TLS1_3);

Actual behavior

ssl_tls13_server downgrades to TLS1.2 regardless of mbedtls_ssl_config.min_tls_version value.

Steps to reproduce

Use some test tls server app, use mbedtls_ssl_conf_min_tls_version() to set minimum version to MBEDTLS_SSL_VERSION_TLS1_3 for the config, then try to connect using TLS1.2-only client.

Additional information

[yanrayw]

Thanks for reporting this issue, we'll look into it soon.