How to Fix "Authentication Error Has Occurred – Function Requested Is Not Supported"

After an update to Windows 10 released back in May 2018, a lot of users who use Remote Desktop function started getting the RDP "authentication error, function requested is not supported" issue where the users get the following error message while logging in to a remote computer via RDP.
"An authentication error has occurred.
The function requested is not supported
Remove computer: [computername]
This could be due to CredSSP encryption oracle remediation."

The issue is a result of a vulnerability, which has been fixed in Windows 10 and Windows 7. If you install update KB4103727 for Windows 10 Version 1709 and KB4103718 for Windows 7, you will start getting this error.

How to fix the RDP Authentication Error Function Requested Is Not Supported error

There are several possible solutions to this issue. We'll go through them one by one.

Install updates on the computer with this issue

The first and the most recommended fix to this error is just to update the PC that's having this problem. Go to Windows Update and check for updates. Install all the updates specifically related to CVE-2018-0886. Moreover, if the computer is running Windows Server 2016, you need to install KB4103723 and if you are using Windows Server 2012 R2, then you have to install KB4103725. A server reboot will be necessary after installing these updates.
If you do not want to update your computer or you cannot do so for some reason then you try some of the solutions outlined below.

Use the Group Policy

  1. Open Run > gpedit.msc to open Group Policy Editor.
  2. Navigate to the following policy path: Computer Configuration > Administrative Templates > System > Credentials Delegation
  3. Open Encryption Oracle Remediation located on the right-hand pane.
  4. Choose Enabled and set the protection level to Vulnerable.
  5. Use the command prompt to run the following command: "gpupdate /force"

This will apply the group policy immediately and you will be able to use Remote Desktop without rebooting the system.

Use the Registry Editor

You can do the same thing as in the above method with the Windows Registry. Just follow these steps:

  1. Launch Run and enter regedit to open Registry Editor.
  2. Navigate to the following key: "HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\System\CredSSP\Parameters"
  3. Edit the DWORD value of AllowEncryptionOracle key to 2. It's on the right pane.

If you can't locate the key for some reason, you will have to create it.

Uninstall the updates from your computer

A simple workaround to the "authentication error, function requested is not supported" is to uninstall the problematic updates from your PC. If you are using Windows 10 Version 1709, you should uninstall the update KB4103727 and KB4103718 if your PC is running Windows 7. You will have to restart your computer to complete the process.

April 24, 2020

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