Windows Server: September 2026 Patch Breaks RDS Servers

The September 2026 cumulative updates for Windows Server 2019, 2022, and 2025 are being blamed by many administrators. The issue: connection problems on RDS servers via Remote Desktop. Here's what we know.

The September 2026 Patch Tuesday seems hard to swallow for some machines running Windows Server, especially RDS servers (Remote Desktop Services). Shortly after these updates were released, users began reporting issues with the following updates: KB5122876 for Windows Server 2019, KB5122882 for Windows Server 2022, and KB5122871 for Windows Server 2025. So all supported versions of Windows Server appear to be affected.

Servers that run for a few hours, then stop working

The scenario described by admins online, especially on Reddit, is always more or less the same. After the update is installed, the RDS server appears to work normally. But after a few hours, things go south. That is when the problems start:

• Existing sessions freeze. Connected users can no longer log off or close their session properly.
• New connections fail. Connection attempts stay stuck on the sign-in screen before eventually failing.
• A forced reboot is sometimes required. Some administrators say a hard reset is the only way to regain control of the server.

"All the Terminal Server systems in our environment fail (sessions drop, no new connection is possible, forced reboot is the only solution) in less than a day", one report reads.

A deadlock between RDP and the session manager?

One admin dug a little deeper on a Windows Server 2022 machine. According to them, the RDP service becomes unresponsive when users log off, due to a mutual block between the Remote Desktop service and the Local Session Manager (LSM). In other words, the disconnecting of the first users may be what pushes the RDS server into an unstable state.

This analysis still needs to be confirmed, because Microsoft has not even officially acknowledged the issue at the time of writing. We will see later today whether the KB page changes accordingly.

For now, the only working fix is the usual drastic one: uninstall the September cumulative update. Those who did report that Remote Desktop Services became operational again. The downside is that this operation removes all security fixes.

Are your RDS servers affected by this issue? Share your feedback in the comments.

Florian Burnel Co-founder of IT-Connect

Systems and network engineer, co-founder of IT-Connect and Microsoft MVP "Cloud and Datacenter Management". I'd like to share my experience and discoveries through my articles. I'm a generalist with a particular interest in Microsoft solutions and scripting. Enjoy your reading.

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