Microsoft Windows Server 2025 build 26100.33451 (KB5129235) is an out-of-band non-security cumulative update released following the September 2026 security update.

What's new

• Fixes a Remote Desktop Services issue introduced after the September 2026 security update that could cause RDS instability.
• Resolves RDP connection and sign-in failures in affected environments.
• Fixes an issue where affected servers could become unresponsive during Remote Desktop configuration.
• Resolves related hangs affecting tools including Microsoft Management Console (MMC), RDS Licensing Diagnoser, File Explorer, and the Windows Update page.
• Fixes certain USB Audio Class 1.0 devices that failed when using multichannel features such as 8-channel or 3D audio modes.
• Includes quality improvements from the September 8, 2026 security update KB5122871.

Known issues

• Some USB Audio Class 1.0 devices may still fail to start, produce no audio, display Device Manager Code 10, or have unavailable volume controls.
• WSUS does not currently display synchronization error details following KB5070881 or later updates while Microsoft addresses CVE-2025-59287.

Recommendation

Organizations affected by Remote Desktop Services instability after the September 2026 security update should prioritize deployment of KB5129235 after expedited validation. Environments that do not use RDS or experience the documented issues can deploy the update through their normal maintenance process.