A major Windows update problem has emerged following Microsoft's September 8, 2026 security updates, with system administrators reporting serious failures affecting Remote Desktop Services (RDS).
The issue can leave the Remote Desktop Services process (TermService) unresponsive, causing RDP connections to fail, login attempts to hang and, in some environments, servers to become effectively inaccessible through remote administration.
Microsoft has now confirmed the issue and released out-of-band updates on September 14 to address the RDS regression across affected Windows versions.
What happened?
The problems began appearing shortly after businesses installed Microsoft's September 8 security updates.
Microsoft's official documentation says that, in affected environments, Remote Desktop Services can become unstable. Administrators have reported symptoms including:
- RDP connections failing after several minutes
- Sign-in failures
- Servers hanging at "Please wait for the Remote Desktop Configuration"
- Remote Desktop Services becoming unresponsive
- Microsoft Management Console (MMC) becoming unresponsive
- RDS Licensing Diagnoser failing to respond
- File Explorer becoming unresponsive
- The Windows Update interface continuously displaying a loading indicator
Reports from administrators have described the underlying TermService process as entering a persistent hung or deadlocked state, sometimes requiring a restart of the affected server to restore access.
However, Microsoft has not publicly characterized the issue specifically as a TermService "permanent deadlock." Its official description is Remote Desktop Services instability.
Which update caused the problem?
The September 8, 2026 Windows security updates introduced the regression.
The affected update depends on the Windows version. For example:
- Windows Server 2025: KB5122871
- Windows Server 2022: KB5122882
- Windows Server 2019: KB5122876
- Windows Server 2016: KB5123099
- Windows 11 24H2/25H2: KB5124008 / related packages
- Windows 10 21H2/22H2: KB5122878
- Older supported Windows Server releases were also affected.
This is particularly serious for companies that depend heavily on RDP for server administration, remote support, virtual desktop infrastructure and access to Windows-based workloads.
Why is an RDP failure so disruptive?
Remote Desktop is more than a convenience for many businesses.
For administrators, RDP may be the primary management path to:
- Windows servers
- Domain infrastructure
- Application servers
- Remote desktops
- Virtual machines
- Infrastructure hosted in private data centers or cloud platforms
If RDS stops responding, administrators can lose their normal management channel.
That creates a particularly unpleasant scenario: the server may still be running, but the administrator can no longer reliably reach it.
For virtual machines without an alternative management path, the problem can become an operational incident rather than simply an inconvenience.
Microsoft noted that, where an affected VM becomes inaccessible through RDP, temporarily stopping/deallocating and restarting the VM may restore connectivity.
Microsoft releases emergency out-of-band fixes
Microsoft responded by releasing a series of out-of-band updates on September 14, 2026.
For example, Windows Server 2025 received KB5129235, which specifically addresses the Remote Desktop Services problem introduced by KB5122871.
Windows Server 2022 received KB5129237, addressing the corresponding RDS issue introduced by KB5122882.
Windows Server 2019 received KB5129238, while Windows Server 2016 received KB5129239.
Microsoft also released corresponding out-of-band updates for Windows 10 and Windows 11, including KB5129236 for Windows 10 21H2/22H2 and KB5129242 for Windows 11 23H2.
The important point for administrators is that this is no longer only a reported regression without a fix. Microsoft has published remediation updates.
What should administrators do?
Companies that installed the September 8 updates should first determine whether their systems are affected.
✅ Check the installed September update
Identify the relevant KB installed on the affected server or workstation.
If the machine is experiencing unexplained RDP instability after the September 8 update, the Microsoft-documented RDS regression should be considered as a possible cause.
✅ Install the appropriate out-of-band update
Microsoft's September 14 releases contain fixes for the RDS issue.
Administrators should apply the appropriate package for their Windows version rather than simply assuming that a different Windows update will resolve the problem.
✅ Maintain an alternative management path
This incident is another reminder that critical servers should not depend exclusively on RDP.
Where possible, companies should maintain alternative administrative access such as:
- Hyper-V or virtualization-console access
- Cloud provider console access
- Out-of-band management
- PowerShell remoting where appropriate
- Windows Admin Center
- Secure management networks or VPN access
The exact architecture will depend on the environment.
✅ Test before broad deployment
Companies using WSUS, Configuration Manager or other enterprise update-management platforms should test cumulative and out-of-band updates against representative workloads before broad deployment when operationally possible.
Security updates remain essential, but patch validation is equally important for infrastructure that cannot tolerate an unexpected management outage.
The bigger lesson for IT teams
The incident highlights a difficult reality of modern infrastructure management.
Security updates are necessary to reduce exposure to vulnerabilities, but updates themselves can occasionally introduce availability or compatibility problems.
For critical infrastructure, businesses therefore need both:
Patch management and operational resilience.
A server that has the latest security update but no alternative management path can still become a significant business risk if a regression breaks remote administration.
The answer is not to stop patching. Instead, companies should build environments where a single faulty component — including Remote Desktop Services — cannot remove the administrator's only path to the system.
Final thoughts
The September 2026 RDP regression demonstrates how quickly a routine security update can become an operational problem at scale.
Microsoft has acknowledged the issue and released out-of-band fixes, so administrators should review systems that received the September 8 updates and deploy the appropriate remediation.
Patching is essential, but resilient infrastructure requires more than a successful update. Businesses should always maintain a tested recovery and management path when critical remote-access services fail.
