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Description of problem:

If we try to use dovecot with TLS v1.3, it fails to accept connections.


Version-Release number of selected component (if applicable):

dovecot-2.2.36-5.el8_0.1.x86_64


How reproducible:

always


Steps to Reproduce:
1. modify /etc/dovecot/conf.d/10-ssl.conf with: ssl_protocols = TLSv1.2 TLSv1.3
2. systemctl restart dovecot
3. openssl s_client -connect localhost:993


Actual results:

dovecot[14857]: imap-login: Fatal: Unknown ssl_protocols setting: Unrecognized protocol 'TLSv1.3'


Expected results:

connection ok

Additional info:

CONNECTED(00000003)
write:errno=104
---
no peer certificate available
---
No client certificate CA names sent
---
SSL handshake has read 0 bytes and written 336 bytes
Verification: OK
---
New, (NONE), Cipher is (NONE)
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
Verify return code: 0 (ok)
---

I believe I did not make this clear, if I replace the "TLSv1.3" setting with "TLSv1.2" then the connection is successful and shows the following:

Post-Handshake New Session Ticket arrived:
SSL-Session:
    Protocol  : TLSv1.3
    Cipher    : TLS_AES_256_GCM_SHA384

For some reason, focing TLS v1.2 results in v1.3.

Bug or "feature"?

dovecot on RHEL8 has been updated to v2.3.8

Part of the update include changes to protocol setting

    "ssl_protocols setting was replaced by ssl_min_protocol. Now you only specify the minimum ssl protocol version Dovecot accepts, defaulting to TLSv1."

Modulo the limits enforced by crypto-policies simply setting "ssl_min_protocol = TLSv1.2" should give the desired result.

Closing, based on comment #3, as it provides the requested functionality and it's the route upstream went.