Published apps and desktops fail to connect after Microsoft September 2026 Windows updates

Symptoms

After the September 2026 Windows updates, users may be unable to connect to published applications or desktops on an affected RD Session Host. Direct RDP connections to the host may also fail.

• New connections remain at Connecting or Welcome.
• RDS or the server may stop responding, including at Please wait for the Remote Desktop Configuration.
• Windows management tools, including Microsoft Management Console and File Explorer, may also stop responding.

Cause

Microsoft confirmed that the September 2026 security updates can destabilize Remote Desktop Services (RDS). When this occurs on a RD Session Host, published sessions may fail to start or complete sign-in.

Resolution

Install the latest Windows cumulative update for the affected server. It contains Microsoft's RDS fix. If you need the September 2026 out-of-band (OOB) update, use the matching update below:

Note: Check the linked Microsoft update page for installation prerequisites, especially for Windows Server 2012 R2 and 2025.

1. Check the affected RD Session Host's Windows Server version and installed updates against the table.
2. During a maintenance window, install the latest cumulative update or the matching OOB update from the Microsoft Update Catalog. The September update does not need to be removed first.
3. Restart the host if required. Update each affected RD Session Host.
4. Confirm the fix is installed, then test a new RAS published session and user sign-in and sign-out.

Reference

Microsoft Windows Server release health: RDS known issue

Microsoft: Troubleshoot RDS instability after the September 2026 Windows updates