[Fixed] RDP Authentication Error: The Function Requested Is Not Supported

The RDP authentication error: The function requested is not supported

While you are using Windows Remote Desktop Connection to remote into another computer, it's not unusual to fail to connect to the remote Windows computer with an error:

• An authentication error has occurred. 
• The function requested is not supported. 
• Remote computer: xxx
• This could be due to CredSSP encryption oracle recommendation. 

How to fix the RDP error - The function requested is not supported

As the RDP authentication error implies, it occurs due to the CredSSP encryption oracle recommendation.  To be specific, when one of the two Windows computers has been updated, repairing the serious vulnerability in CredSSP protocol and the other one hasn't been updated, Remote Desktop authentication error happens are you can't connect to a PC with a vulnerable version of CredSSP.

To fix the Remote Desktop the function requested is not supported error, you can update the computer that is running a vulnerable version of CredSSP or try one or more fixes in the following content. 

Fix 1.  Disable Network Level Authentication in Remote Desktop setting

You can disable Network Level Authentication (NLA) for Remote Desktop on the remote computer that is running Windows 11/10/8.1/8/7.

Note: NLA completes user authentication before you establish a remote desktop connection and is helpful in protecting the remote computer from malicious users and software. 

Step 1. Press "Windows" and "R" to open Run box, input "sysdm.cpl" and click Enter to open the "System Properties" window.

Step 2. Click "Remote", locate “Allow connections only from computers running Remote Desktop with Network Level Authentication (recommended)”  and uncheck it.

Step 3. Click "Apply" and try to connect again.

Fix 2. Change the protection level to vulnerable from Group Policy

If it's unavailable for you to update OS or uncheck "Allow connections only from computers running Remote Desktop with Network Level Authentication", you can change settings on your local computer to temporarily allow a less-secure connection. 

Step 1. Press "Windows" and "R" to open Run box and type “gpedit.msc”, then press "Enter" to open the "Group Policy Editor" window.

Step 2. Go to "Computer Configuration" > "Administrative Templates" > "System" > "Credentials Delegation" on the left of the Group Policy Editor window.

Step 3. Choose "Enabled" and select "Vulnerable" from "Protection Level", and then click "OK".

 About the three protection levels:

• Force Updated Clients:  The highest level of protection, requires applying the update to all clients you are going to communicate with CredSSP.
• Mitigated: It blocks apps like RDC to connect to servers that don't have the update. 
• Vulnerable: The lowest level of protection, allows you to connect to a remote server using RDP and expose the servers to the attacks.

Fix 3. Change the protection level to vulnerable from Registry Editor

You can also try to change the protection level to vulnerable from Registry Editor to solve the Authentication error due to CredSSP encryption oracle recommendation. Please follow the below steps to edit.

Step 1. Press Windows key and R to open the run box, and type “regedit” to open the "Registry Editor". 

Step 2. Go to the following path:

Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\CredSSP\Parameters.

Step 3. Double-click the “AllowEncryptionOracle” in the right of the window and set the value to 2 to set the protection level to vulnerable.

Note: "0" refers to "Force Updated Clients", "1" means "Mitigated" and 2 present "Vulnearable".

Fix 4. Remove alternative updates

As this problem usually occurs after a windows update, you can remove alternative updates to solve the RDP authentication the requested is not supported error.

Step 1. Open the run box by pressing the Windows key and R, then enter “appwiz.cpl” to open the "Programs and Features" window.

Step 2. Click "View installed updates" on the left side of the window to open the "Installed Updates" window.

Step 3. Search KB4103727 or KB4103718 update and double-click it to uninstall.

An easy workaround to RDP The function requested is not supported error

If all the fixes can't deal with the RDP authentication error, it's recommended to apply third-party remote desktop freeware, AnyViewer. Click the button and download it on your computers. 

Note: You can start remote control from iOS/Android via AnyViewer.

Now, check out how to use it to remotely access another computer over the internet. 

Step 1. Install and run the app on your devices. Go to "Log in" > "Sign up" to create an AnyViewer account and then log into the account on both devcis. 

Step 2. Locate the Windows computer you want to access, click it and choose "Remote control".

Quickly, you can connect to the remote computer and take operations as you were sitting in front of it. 

Note: If you want to access a remote computer for offering technical support just once, you can send a control request to your partner and the person on the other end needs to accept the request. 

Conclusion

Surely you have realized the possible cause and valid fixes for Remote Desktop authentication error- The function requested is not supported error. What you need to pay attention to is that disabling NLA or changing the protection level may risk exposing the server to the attack.  Therefore, if you that RDP authentication error still occurs after updating OSes on both computers, it's highly recommended to use the free and secure remote desktop software, AnyVeiwer.