I didn't try on a
fresh CentOS 8 install, but I've checked with this command to 127.0.0.1 on an older internal test box, and no matter what I do, before and after a full yum update, exim rebuild, /etc/exim_dh.pem deletion + auto download, or manual rebuild with `/usr/bin/openssl dhparam -out /etc/exim_dh.pem 4096`, I always get the same result:
Code:
[root@es8-64-personal custombuild]# nmap --script ssl-enum-ciphers -p 465 127.0.0.1
Starting Nmap 7.70 ( https://nmap.org ) at 2021-07-20 21:24 EDT
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00012s latency).
PORT STATE SERVICE
465/tcp open smtps
| ssl-enum-ciphers:
| TLSv1.2:
| ciphers:
| TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (ecdh_x25519) - A
| TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (ecdh_x25519) - A
| TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256 (ecdh_x25519) - A
| TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 (dh 4096) - A
| TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 (dh 4096) - A
| compressors:
| NULL
| cipher preference: server
|_ least strength: A
So the configs and any combination of the /etc/exim_dh.pem file does not seem to affect it for me. It does indicate that these settings "can be correct" for whatever combination of things I've got here.
The old openssl version was:
OpenSSL 1.1.1c FIPS 28 May 2019
and the latest version:
OpenSSL 1.1.1g FIPS 21 Apr 2020
but neither had any effect... it always included TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 and TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 in the output.
To expand on the previous reply, the tls_dhparam value also support "none" and "default". If removing the tls_dhparam variable solves it, then perhaps adding tls_dhparam=default to the /etc/exim.variables.conf.custom and rewriting the exim.conf may have an effect. I believe that uses the internal dh primes (or something like that).
This internal box does not get any LetsEncrypt updates, so I wasn't able to rule out a LetsEncrypt certificate update possibly being related.
I know a while back we went from a default of 4096-bit LE keys, to now defaulting to a EC-384 key. Related? I've not ruled it out (didn't test between the 2). The old box I'm on uses the older 4096-bit cert key (self-signed, I believe).
I'm going to bump the thread to Martynas in case he has any ideas.
Perhaps creating a ticket with root login may be useful to try and narrow it down.
John
Starting May 4, 2021
