Unable to connect to SQL Server from one machine; "an existing connection was forcably closed by the remote host"

Question

Connecting to the SQL Server (2008 R2 SP3 - KB 4057113) with SSMS version 18 yields:

A connection was successfully established with the server, but then an error occurred during the login process. (provider: SSL Provider, error: 0 - An existing connection was forcibly closed by the remote host.) (.Net SqlClient Data Provider)

---

For help, click: http://go.microsoft.com/fwlink?ProdName=Microsoft%20SQL%20Server&EvtSrc=MSSQLServer&EvtID=10054&LinkId=20476

---

Error Number: 10054 Severity: 20 State: 0

Connection failure logging is enabled on the server but nothing gets logged. Please note the for help link is dead. I've tried various database applications. Nothing gets through. The problem appears to be on the server, not the workstation, but other workstations can connect to the server. This workstation can also connect to other servers.

I've got a good guess this is somehow TLS related, because that's what it was last time (server didn't support TLS 1.2 and needed a patch). This time I can't find the problem though.

Answer 1

Found the problem. SQL Server 2008 R2 really wants to use a cert signed with SHA1. If SHA1 certs are disabled, you can't connect.

The master dev db needs to be at the oldest version supported by the vendor. Windows had disabled SHA-1 over https in a different way than just turning off RSA/SHA1 crypto algorithm so it turns out that leaving it enabled isn't unsafe (for our purposes).