SSL_ERROR_UNSUPPORTED_VERSION when attempting to debug with IIS Express

Question

Created a new template ASP.Net Core 3.1 MVC web app. When I attempt to debug it using IIS Express I get the following error in firefox:

Secure Connection Failed

An error occurred during a connection to localhost:44354. Peer using unsupported version of security protocol.

Error code: SSL_ERROR_UNSUPPORTED_VERSION

I attempted to delete all of my localhost certificates with MMC, repair IIS Express to install a new one. When attempting to debug it asks me to trust the certificate, I press yes, but this error still appears.

I am on windows 7 if that matters.

Answer 1

As far as I know, this issue is related with Firefox, the firebox doesn't support the tls 1.0 and tls 1.1.

To solve this issue, I suggest you could try below solutions:

1. Enter about:config into the firefox address bar (confirm the info message in case it shows up) & search for bold preferences starting with security.

2. Set security.tls.version.min (from 2 to 1)

Answer 2

I was having that same issue in Firefox, after checking the answer of Brando Zhang, I try only changing the security.tls.version.enable-deprecated to true (in about:config) and it worked!

That way, you don't have to lower the TLS security version