# Remote Desktop: An authentication error has occurred. The function requested is not supported. This could be due to CredSSP encryption oracle remediation

**Code:** `CredSSP encryption oracle remediation` · **Category:** Windows · **Seen on:** Windows

The RDP client and server disagree on CredSSP security updates — one side is patched and enforcing, the other isn’t.

## Meaning

After the CVE-2018-0886 updates, patched clients refuse to connect to unpatched servers (and vice versa depending on policy). The real fix is updating the server; a temporary client policy can relax it.

## Common causes

- Server missing CredSSP security updates
- Client policy set to Force Updated Clients
- NLA/CredSSP misconfiguration

## Quick fix

1. Install current Windows updates on the server
2. Temporarily set Encryption Oracle Remediation to Vulnerable on the client (then revert)
3. Use the console/Hyper-V/Azure serial console to patch the server

## Detailed fix by platform

### Windows

1. `reg add HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\CredSSP\Parameters /v AllowEncryptionOracle /t REG_DWORD /d 2 /f   # temporary; revert after patching`

## How to diagnose

1. **Patches** — Server patch level
2. **Policy** — Encryption Oracle Remediation setting on both sides

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Source: [WhatIsMyError](https://whatismyerror.com/errors/windows/rdp-credssp-encryption-oracle)