I got ERR_SSL_VERSION_OR_CIPHER_MISMATCH (chrome) or SSL_ERROR_NO_CYPHER_OVERLAP (firefox) for example on accessing the URL https://sesion.telecom.com.ar/
.
Disabling TLS 1.3 downgrade hardening in Chrome helped:
This option enables the TLS 1.3 downgrade hardening mechanism. This hardens TLS 1.3 connections while remaining compatible with TLS 1.0 through 1.2 connections. Firewalls and proxies that do not function when this is enabled do not implement TLS 1.0 through 1.2 correctly or securely. They must be fixed by vendors. – Mac, Windows, Linux, Chrome OS, Android
To disable and re-enable it open following URL in Chrome (works for version 74, but not for canary version 76): chrome://flags/#enforce-tls13-downgrade
In Firefox goto about:config
and search for security.tls.version.fallback-limit
set it temporarily to 1.
Make sure to turn it back again later.
1
I'm guessing old SSL config server side. And new browser client side. => Investigate with SSL checkers: (1) If it's a publicly reachable website run it through https://sslping.com/ (2) if it's an internal website try this linux script: https://testssl.sh/
– StackzOfZtuff – 2019-01-31T12:13:41.507