Microsoft Windows Server 2025 Update Version OS Build 26100.33438
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Update Summary
KB5122871 (OS Build 26100.33438) delivers the latest security fixes and quality improvements for Windows Server 2025, including updates from KB5120233. It also improves certificate compatibility, networking failover, Remote Desktop audio redirection, and Sysmon reliability. Reference IDs: KB5122870, CVE-2025-59287.
Update Details
Security
- Includes the latest security fixes for Windows Server 2025.
- Windows Secure Boot certificate updates are being delivered to help devices continue to start normally as certificates expire starting in June 2026.
Bug Fixes
- Improves application compatibility during Windows certificate-authority updates.
- Adjusts Morocco Standard Time for the transition to permanent UTC+00:00 on Sep 20, 2026.
- Improves network failover so connections respond more quickly when a network adapter is disconnected.
- Improves Remote Desktop audio redirection so audio from remote sessions plays correctly on the local device.
- Improves Sysmon Process Tampering detection by reducing false Event ID 25 alerts for normal
smss.exeactivity. - Improves Sysmon reliability for file monitoring and file archiving when archive directories are unavailable.
- Improves Sysmon executable file validation for more consistent tampering detection.
Known Issues
- WSUS does not display synchronization error details after installing KB5070881 or later updates; this is temporarily removed to address CVE-2025-59287.
Hints
- This cumulative update includes non-security updates from KB5120233.
- If previous updates are already installed, only the new updates in this package will be downloaded and installed.
- Includes a servicing stack update: KB5122870 (OS Build 26100.33434).
Product Information
Vendor: Microsoft
Product: Windows Server 2025
Product type: Software
Application category: Utilities
Platform: Windows
Version: OS Build 26100.33438
Vendor release date: Sep 8, 2026
Original release notes: View on vendor site
Published on updatealert.io: Sep 9, 2026
Description: Server operating system for next-generation on-premises and hybrid workloads.