September 2026 Patch Tuesday Is Breaking Remote Desktop…

The short version

The September 2026 Patch Tuesday cumulative updates — KB5122876 for Server 2019, KB5122882 for Server 2022, and KB5122871 for Server 2025 — are causing Remote Desktop Services to hang and stop accepting connections. Servers typically work for a few hours after the update, then fail. Microsoft shipped out-of-band fixes on 14 September 2026: KB5129238 (Server 2019), KB5129237 (Server 2022, build 20348.5631) and KB5129235 (Server 2025, build 26100.33451), plus KB5129243 for Server 2012 R2. KB5122882’s known-issue entry now reads “resolved in Windows updates released on and after September 14, 2026 such as KB5129237”. Install the out-of-band update for your release rather than rolling back and losing the month’s security fixes.

⚠ Action required for RDS teams: If you have not yet deployed the September 2026 Patch Tuesday updates to Windows Server machines running Remote Desktop Services, hold that deployment now. Validate your environment carefully before proceeding. Superseded — Microsoft resolved this with out-of-band updates on 14 September 2026 (KB5129238 for Server 2019, KB5129237 for Server 2022, KB5129235 for Server 2025, KB5129243 for Server 2012 R2). Apply the one for your release. The hold-and-roll-back guidance below applies only to the window before those shipped.

What is happening

Windows Server administrators are reporting a serious regression after installing the September 2026 Patch Tuesday cumulative updates. Remote Desktop Services (RDS) — the component that enables users to connect to servers via Remote Desktop Protocol (RDP) and Terminal Services — is failing after the update is applied.

The failure is not immediate. Servers typically continue accepting Remote Desktop connections normally for a few hours after the update is installed. The problems begin once users start logging out. After the first batch of logouts, the Remote Desktop Services stack enters an unresponsive state. Existing sessions become unable to disconnect or log off cleanly. New connection attempts hang at the connection screen and eventually fail. In some cases, the only way to recover the server is a hard reset.

One administrator debugging the issue on Server 2022 identified what appears to be a deadlock inside the RDP service stack. The service hangs at RDPSERVERBASE!WDLIB_Close with no timeout configured, creating a deadlock between the Remote Desktop service and the Local Session Manager (LSM). Microsoft has not confirmed this as the definitive root cause, but the behaviour matches what multiple administrators are independently observing.

📋 Note: This is a community-reported issue. BleepingComputer reported it on 10 September 2026 based on administrator reports from Reddit threads and reader submissions. Microsoft subsequently documented it and shipped out-of-band fixes on 14 September 2026. Note that Windows 365 and Azure Virtual Desktop are not affected.

The issue affects all three current Windows Server releases and has been reproduced across multiple independent environments, covering Terminal Server deployments and general RDS configurations.

Who is affected

Any Windows Server running Remote Desktop Services that has received the September 2026 Patch Tuesday update is at risk. The issue is not tied to a specific hardware configuration, hypervisor, or third-party software — it follows the update across different environments.

Windows Server version	Update KB	Affected?
Windows Server 2019	KB5122876	✅ Yes — confirmed affected
Windows Server 2022	KB5122882	✅ Yes — confirmed affected
Windows Server 2025	KB5122871	✅ Yes — confirmed affected
Servers not yet patched with September 2026 updates	N/A	❌ Not yet affected — hold deployment
Client Windows 11 / Windows 10 devices	Yes	✅ Also affected — Microsoft shipped client out-of-band fixes for the same bug: KB5129236 (Windows 10 21H2/22H2), KB5129195 (Windows 11 24H2/25H2), KB5129194 (Windows 11 26H1)
Windows 365 / Azure Virtual Desktop	No	❌ Microsoft states these are not affected

Administrators running Terminal Server farms where users log in and out throughout the day are the most heavily impacted, as the failure mode is triggered by user logouts. Servers that see low session turnover may not exhibit the problem until enough logouts have occurred.

How to tell if your environment is affected

The most direct way to confirm exposure is to check which September 2026 updates are installed on your RDS servers. You can do this from an elevated PowerShell session on each server.

PowerShell — Run as Administrator on RDS server

# Check if the September 2026 update is installed on Server 2019 Get-HotFix -Id KB5122876 # For Server 2022 Get-HotFix -Id KB5122882 # For Server 2025 Get-HotFix -Id KB5122871 # Returns the hotfix entry if installed # Returns nothing (no output) if NOT installed

If the relevant KB is returned, the update is installed and RDS is at risk. To check the current state of the Remote Desktop Services stack, run the following:

PowerShell — Check RDS service state

# Check the three core RDS services Get-Service TermService, SessionEnv, UmRdpService | Select-Object Name, DisplayName, Status # Healthy output: # TermService Remote Desktop Services Running # SessionEnv Remote Desktop Configuration Running # UmRdpService Remote Desktop Services UserMode... Running # Affected output after the deadlock occurs: # TermService Remote Desktop Services Stopped (or Paused) # Note: a server restart may NOT restore the service # Rolling back the update is the confirmed recovery - restart alone does not always fix this

When the deadlock has occurred, the Event Viewer System log will contain errors from the TermService source. Look for these in the hours following user logouts:

⚠ Error — System Event Log — Source: TermService

Log: System
Source: TermService
Level: Error / Critical
Message: The Remote Desktop Services service terminated unexpectedly. This has occurred N time(s). The following corrective action will be taken in X milliseconds.
Related: Look for preceding SessionEnv errors indicating the Local Session Manager stopped responding during a logoff sequence

⚠ Gotcha: The failure is triggered by user logouts, not logins. A server that looks stable immediately after the update — because users have been logging in but not yet logging out — can enter the deadlock state hours later when the day’s first wave of logoffs begins. Do not assume a server is unaffected just because it worked normally for the first few hours post-update.

What you can do now

There is no official Microsoft-provided workaround as of 11 September 2026. The options available to administrators are to hold unpatched servers, roll back the update on patched servers, or keep servers patched while accepting the stability risk and monitoring closely.

Option 1 — Hold deployment (safest, for servers not yet patched):

If you have not yet deployed KB5122876, KB5122882, or KB5122871 to your RDS servers, pause that deployment in your patching tool (Windows Server Update Services, Microsoft Endpoint Configuration Manager, or Intune) until Microsoft confirms a resolution. This is the lowest-risk option and requires no change to already-deployed servers.

✅ Tip: Before resuming deployment, validate in a non-production RDS server by installing the update, running a full day of logon/logoff cycles, and confirming that Remote Desktop Services remain healthy after logouts. Only then promote to production.

Option 2 — Roll back the update (for servers already patched):

Administrators who have already deployed the September update and are experiencing failures can uninstall the cumulative update to restore Remote Desktop Services. On Windows Server, cumulative updates can be removed from an elevated Command Prompt or PowerShell session:

Command Prompt — Run as Administrator (select the correct KB for your OS)

# PREFERRED: install the 14 Sep out-of-band fix for your release instead of rolling # back - KB5129238 (2019), KB5129237 (2022), KB5129235 (2025). # # If you must remove the September LCU, wusa.exe /uninstall will NOT do it: # quiet uninstall is deprecated on Server 2016+ (fails with Setup event ID 8) # and wusa cannot remove a combined SSU+LCU package. Use DISM instead: Get-WindowsPackage -Online | Where-Object { $_.PackageName -like '*RollupFix*' } DISM /online /Remove-Package /PackageName:<LCU package identity from above> # The commands below are retained for reference only and are expected to fail. # Windows Server 2019 — uninstall KB5122876 wusa.exe /uninstall /kb:5122876 /quiet /norestart # Windows Server 2022 — uninstall KB5122882 wusa.exe /uninstall /kb:5122882 /quiet /norestart # Windows Server 2025 — uninstall KB5122871 wusa.exe /uninstall /kb:5122871 /quiet /norestart # After the uninstall completes, restart the server # wusa /quiet suppresses the UI; /norestart lets you control the reboot window # Confirm removal with: Get-HotFix -Id KB5122876 (should return no output)

⚠ Warning: Rolling back the September 2026 cumulative update removes all security patches included in that release, including fixes for actively exploited vulnerabilities. This is a stability-vs-security trade-off. Assess your organisation’s risk posture before rolling back, and plan to reapply the patched update as soon as Microsoft provides a resolution. Consider additional network controls (firewall rules, VPN restrictions) to reduce exposure while RDS servers are in an unpatched state.

Option 3 — Open a Microsoft support case:

If your organisation is running RDS in a production environment with no ability to roll back, opening a support case with Microsoft is the appropriate path. Microsoft has acknowledged the reports and is investigating. A support case escalates the issue within Microsoft’s engineering teams and may surface a workaround (such as a specific registry key or service configuration) before a patched update is available.

Microsoft’s response

Microsoft confirmed to BleepingComputer on 10 September 2026 that it is aware of the reports and is actively investigating. No official Knowledge Base article, release-health entry, or workaround has been published for this issue as of 11 September 2026. The Windows Server release health dashboards on Microsoft Learn are the authoritative location for official updates:

Until a patched cumulative update or official workaround is available, the recommendation is to hold the September 2026 updates on any RDS server, roll back on servers already affected, and monitor the release health dashboards for updates.

References

Last reviewed: 11 September 2026. This post will be updated when Microsoft publishes an official fix or workaround.

September 2026 Patch Tuesday Is Breaking Remote Desktop Services on Windows Server