KB 4093492 Broke my RDP sessions.

Microsoft has released another patch causing issues or is it?  the KB 093492 patch is a good thing you just need to patch your servers.

Credential Security Support Provider protocol (CredSSP) is an authentication provider that processes authentication requests for other applications.

A remote code execution vulnerability exists in unpatched versions of CredSSP. An attacker who successfully exploits this vulnerability could relay user credentials to execute code on the target system. Any application that depends on CredSSP for authentication may be vulnerable to this type of attack.

This security update addresses the vulnerability by correcting how CredSSP validates requests during the authentication process.

This is a planned tightening of security over three months. As promised, the May update changed the default to Mitigated. You can use group policy or regis“Initially in March, they are rolling out the new protocol. Later in April they will make it so that an error message will occur when you attempt to remote from a patched machine to an unpatched machine, and then later in May (tentative at this time) the default will be to enforce that remoting from a patched machine to an unpatched machine will not work.”