Introduction
This procedure enables the usage of less secure communication methods. This is not a recommended security practice and anyone requiring these changes should discuss this matter with a qualified system administrator prior to implementing them; a list of system administrators is available here:
System Administration Services
If you upgrade your server to CentOS 8 or CloudLinux 8 and require TLS 1.0 or TLS 1.1, here are the steps on how to enable them.
CentOS 8 and CloudLinux 8 use the Crypto Policy "DEFAULT", which only allows TLS 1.2+. To enable TLS 1.0/1.1 support the policy needs to be set to "LEGACY"
Here is the documentation on the Crypto Policy changes:
CHAPTER 4. USING SYSTEM-WIDE CRYPTOGRAPHIC POLICIES
Procedure
To change the Crypto Policy, run this command, then restart the server:
update-crypto-policies --set LEGACY
In WHM >> Service Configuration >> Exim Configuration Manager >> Basic Editor, make the following changes, as outlined here:
Where do I edit the Exim Configuration?
Change these settings:
- Allow Weak SSL/TLS Ciphers set to On
- Options for OpenSSL set to +no_sslv2 +no_sslv3
- SSL/TLS Cipher Suite List must contain this string:
-
ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA:ECDHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-RSA-AES256-SHA256:DHE-RSA-AES256-SHA:ECDHE-ECDSA-DES-CBC3-SHA:ECDHE-RSA-DES-CBC3-SHA:EDH-RSA-DES-CBC3-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:DES-CBC3-SHA:!DSS
The changes can be confirmed with this nmap command:
nmap --script ssl-enum-ciphers -p 465 <ip_address_or_hostname>
Note: you can learn how to use nmap here:
How to use nmap to troubleshoot port connectivity issues
The output should appear similar to the following if properly applied:
Starting Nmap 6.40 ( http://nmap.org ) at 2021-03-30 00:21 CDT
Nmap scan report for 1.2.3.4
Host is up (0.0018s latency).
PORT STATE SERVICE
465/tcp open smtps
| ssl-enum-ciphers:
| SSLv3: No supported ciphers found
| TLSv1.0:
| ciphers:
| TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA - strong
| TLS_DHE_RSA_WITH_AES_128_CBC_SHA - strong
| TLS_DHE_RSA_WITH_AES_256_CBC_SHA - strong
| TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
| TLS_RSA_WITH_AES_128_CBC_SHA - strong
| TLS_RSA_WITH_AES_256_CBC_SHA - strong
| compressors:
| NULL
| TLSv1.1:
| ciphers:
| TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA - strong
| TLS_DHE_RSA_WITH_AES_128_CBC_SHA - strong
| TLS_DHE_RSA_WITH_AES_256_CBC_SHA - strong
| TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
| TLS_RSA_WITH_AES_128_CBC_SHA - strong
| TLS_RSA_WITH_AES_256_CBC_SHA - strong
| compressors:
| NULL
| TLSv1.2:
| ciphers:
| TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA - strong
| TLS_DHE_RSA_WITH_AES_128_CBC_SHA - strong
| TLS_DHE_RSA_WITH_AES_128_CBC_SHA256 - strong
| TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 - strong
| TLS_DHE_RSA_WITH_AES_256_CBC_SHA - strong
| TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 - strong
| TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 - strong
| TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong
| TLS_RSA_WITH_AES_128_CBC_SHA - strong
| TLS_RSA_WITH_AES_128_CBC_SHA256 - strong
| TLS_RSA_WITH_AES_128_GCM_SHA256 - strong
| TLS_RSA_WITH_AES_256_CBC_SHA - strong
| TLS_RSA_WITH_AES_256_CBC_SHA256 - strong
| TLS_RSA_WITH_AES_256_GCM_SHA384 - strong
| compressors:
| NULL
|_ least strength: strong
Nmap done: 1 IP address (1 host up) scanned in 0.87 seconds