Remote Desktop: An authentication error has occurred. The function requested is not supported.

Issue:

When trying to establish Remote Desktop(RDP) connection to a server or computer, you get error “An authentication error has occurred. The function requested is not supported.”

 

Cause 1:

Microsoft has released an update on March 2018 to fix an issue with CredSSP, “Remote Code Execution” vulnerability (CVE-2018-0886) which affect RDP connections. If one of the following updates are installed on the client or server, the RDP connection attempt will fail with this error.

Windows 10: KB4103716, KB4088779, KB4103723, KB4103731, KB4103727, KB4103721, KB4103716

Windows 8.1: KB4103725, KB4103715

Windows 7: KB4103718, KB4103712

Windows Server 2008: KB4056564 Windows Server 2008 R2: KB4103718, KB4103712

Windows Server 2012: KB4103730, KB4103726 Windows Server 2012 R2: KB4103725, KB4103715

 

Resolution/ Fix: 

Option 1:

Ensure both client & server side have above patch installed so that RDP can be established in a secure way.

The update can be downloaded for each operating system here: https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2018-0886

 

Option 2:

Change the following registry key to allow unsecured RDP connection

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\System\CredSSP\Parameters

DWORD: AllowEncryptionOracle

Value: 2