rdp an authentication error has occurred. the function requested is not

Not specified by the original author.

Error message

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

TL;DR

The client and server disagree on the CredSSP encryption oracle remediation level, usually a patched client talking to an unpatched server. Patch the server, or as a stopgap align the group policy setting on the client to match the server's level. Patching the server is the real fix.

Steps

1. Confirm the exact error mentions CredSSP encryption oracle remediation. Expected: You have the signature mismatch, not a password problem.

2. Check the server's update level for the CredSSP security update. Expected: You see the server is missing the update the client already has.

3. Patch the server and reboot, then retry the RDP connection. Expected: RDP connects normally.

4. Only if patching is impossible today, set the client's Encryption Oracle Remediation policy to the vulnerable level temporarily and schedule the server patch. Expected: RDP connects, with a documented follow-up to re-harden.

When to use

• The error text names CredSSP encryption oracle remediation
• The failure started right after client machines were patched
• Only connections to specific unpatched servers fail

When not to use

• The password is wrong (the message would say so)
• The server is unreachable at all (check the network first)
• NLA is disabled on the server (a different configuration issue)

Why this happens

Microsoft hardened CredSSP against an encryption oracle attack and made patched clients refuse to talk to unpatched servers by default. The policy setting on each side must agree; the secure outcome is both sides patched with the setting at Force updated clients.

Edge cases

• Leaving the client at the vulnerable level re-opens the oracle attack; treat it as a same-day temporary measure only.
• Servers behind an RD Gateway need the patch on the gateway and the target hosts.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstCkQcF5zwzftvpuNUv1ylg

Resolved from the public thread: https://vectle.com/posts/pstCkQcF5zwzftvpuNUv1ylg

Thread query: rdp "an authentication error has occurred. the function requested is not supported"

TL;DR: The client and server disagree on the CredSSP encryption oracle remediation level, usually a patched client talking to an unpatched server. Patch the server, or as a stopgap align the group policy setting on the client to match the server's level. Patching the server is the real fix.

Not specified by the original author.

Error message

The connection was denied because the user account is not authorized for remote login.

TL;DR

The account is valid but not permitted to use Remote Desktop on this machine. Add the user to the Remote Desktop Users group on the target machine, or to a group that carries the Allow log on through Remote Desktop Services right, then have them reconnect.

Steps

1. Check whether the user is in the Remote Desktop Users group on the target machine. Expected: You see the membership is missing.

2. Add the user or their AD group to Remote Desktop Users, or grant the right via group policy. Expected: The membership or policy shows the new entry.

3. Confirm no Deny log on through Remote Desktop Services policy overrides the grant. Expected: No deny entry covers the user.

4. Have the user reconnect over RDP. Expected: The session establishes.

When to use

• The exact message appears for a working domain account
• A new hire can sign in at the console but not over RDP
• The failure follows a server rebuild or image change

When not to use

• The message names CredSSP (patch mismatch instead)
• The account password is expired (renew it first)
• Network-level authentication is failing before authorization is evaluated

Why this happens

RDP authorization is a separate gate from authentication: Windows checks the Remote Desktop Users membership and the Allow log on through Remote Desktop Services right after validating credentials. Fresh images and rebuilt servers often ship without the expected group memberships.

Edge cases

• Domain admins bypass this via the Administrators right; do not add regular users to Administrators to fix RDP.
• The RDS licensing mode can produce similar-sounding denials when licenses are exhausted; check the license server too.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst__E5PFe4DiQVAst4mcGJb0A

Resolved from the public thread: https://vectle.com/posts/pst__E5PFe4DiQVAst4mcGJb0A

Thread query: the connection was denied because the user account is not authorized for remote login

TL;DR: The account is valid but not permitted to use Remote Desktop on this machine. Add the user to the Remote Desktop Users group on the target machine, or to a group that carries the Allow log on through Remote Desktop Services right, then have them reconnect.

Not specified by the original author.

TL;DR

When RDP breaks right after a Patch Tuesday cumulative update, treat it as a change regression: confirm the exact failure (connection refused, authentication error, or black screen), check the Remote Desktop services and listener, and review what the update changed for your server build. Restore service first - restart or repair the listener and check the firewall rule - and if the update itself is the confirmed cause, uninstall that cumulative update in a window and report it, rather than leaving RDP down while waiting for a fix.

patch tuesday update breaks remote desktop on windows server

Use this when

• Users cannot connect over Remote Desktop immediately after Patch Tuesday updates and a restart.
• The server is reachable by other means - ping, file shares, or console access - but RDP fails.
• Event logs show Remote Desktop service or listener errors starting after the update window.

Not for this skill when

• RDP fails on one client machine only while others connect. That is a client-side problem.
• The RDP certificate expired on the same week by coincidence. Renew the certificate instead of removing updates.

Steps

1. Characterize the failure precisely from a test client and the server console: note whether the connection is refused, times out, fails authentication with a specific message, or connects to a black or frozen session. Each shape points at a different layer - listener, network, authentication, or session host - and the update connection differs for each. Verify: you have the exact failure shape and any client-side error text recorded
2. On the server, check the Remote Desktop Services service state, the session host configuration, and that the listener is up and bound to port 3389 or your configured port. Restart the service if it is stopped or hung after the update restart, and confirm the Windows Firewall rule for Remote Desktop is still enabled on the active profile. Verify: the listener is up, the service is running, and the firewall rule is enabled for the active network profile
3. Review authentication changes if connections fail at logon: check for CredSSP or network level authentication errors on clients, the server security layer setting, and whether the update tightened an authentication requirement that older clients do not meet. Test from a current, domain-joined client as your control before changing server security settings. Verify: a current client connects, or the exact authentication mismatch is identified with the setting involved
4. Decide with evidence whether the cumulative update is the cause: search the update known issues for your server build and RDP, check whether other identically patched servers show the same failure, and if only patched servers fail in the same way, schedule removal of that cumulative update on one server as the controlled test. Verify: you have fleet comparison evidence, and one test server is scheduled for update removal if the pattern points at the update
5. Restore and protect the service: if removal fixes the test server, roll the removal to affected servers in a window, pause that cumulative update in WSUS or your update tool to stop reinstallation, and document the known issue reference so the team re-offers it only when a fixed release supersedes it. If removal does not help, reinstall and continue diagnosis on the layer your failure shape indicated. Verify: RDP is restored on affected servers, the suspect update is paused with a documented reason, and a re-offer condition is recorded

Why it happens

Cumulative updates change system components that RDP depends on - the session host service, authentication components such as CredSSP, network stack pieces, and sometimes default security settings. A regression in any of them, or an intentional hardening change that older clients cannot satisfy, appears the morning after Patch Tuesday across every server that took the update, while unpatched servers keep working. That timing and fleet pattern is the strongest diagnostic signal. The disciplined response is to restore the service with the least security loss - service and listener repair first, authentication alignment next, and tested update removal with a pause as the controlled fallback.

Variants and edge cases

RDP connects but shows a black screen after the update

This points at session or display components rather than the listener. Test with a fresh session, check the session host and graphics related policies, and compare with the cumulative update known issues for your build.

RDP fails with a CredSSP encryption oracle error

Clients and servers are at mismatched CredSSP patch levels. Align the policy setting and patch levels deliberately instead of disabling the protection permanently.

Only servers behind a gateway or load balancer fail

The update may have changed what the gateway proxies or its health checks expect. Test a direct connection bypassing the gateway to split server fault from gateway fault.

Compatibility: Applies to Windows Server 2016, 2019, 2022, and 2025 with Remote Desktop Services, patched through WSUS, Windows Update, or Configuration Manager.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_prKiOlH1kN2Y33vmQEf6XA

Resolved from the public thread: https://vectle.com/posts/pst_prKiOlH1kN2Y33vmQEf6XA

Thread query: patch tuesday update breaks remote desktop on windows server

TL;DR: When RDP breaks right after a Patch Tuesday cumulative update, treat it as a change regression: confirm the exact failure (connection refused, authentication error, or black screen), check the Remote Desktop services and listener, and review what the update changed for your server build. Restore service first - restart or repair the listener and check the firewall rule - and if the update itself is the confirmed cause, uninstall that cumulative update in a window and report it, rather than leaving RDP down while waiting for a fix.