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KB5124012: Overview with user sentiment and feedback

Last Updated October 12, 2026

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Known Issues

Overview

KB5124012 is a September 8, 2026 cumulative security update for Windows 11 version 26H1 (OS Build 28000.2954). It includes security fixes, quality improvements, and non-security updates from the prior month's preview release. This update applies to all editions of Windows 11 version 26H1 and includes servicing stack update KB5125104.

General Purpose

  • Security updates addressing multiple vulnerabilities
  • Secure Boot certificate deployment expansion for eligible devices
  • Fixed Teams and Outlook crashes on Arm64-based PCs
  • Morocco Standard Time adjustment for permanent UTC+00:00 transition (effective Sept 20, 2026)
  • Remote Desktop audio redirection fixes for certain configurations
  • OMA-DM client logging improvements with certificate chain information

General Sentiment

This update addresses critical functionality issues and security vulnerabilities, but carries significant known issues that warrant caution. Multiple post-release problems have been documented affecting domain trust, audio devices, Remote Desktop Services, and virtual machine file sharing, though some have been partially resolved by subsequent out-of-band updates.

Known Issues

  • Devices may experience black screen or desktop loading issues after sign-in (especially on Azure Virtual Desktop with FSLogix)
  • Domain-joined Credential Guard-protected machines may lose secure channel with Active Directory (resolved by KB5124010)
  • USB Audio Class 1.0 devices may fail to start or produce no sound (partially resolved by KB5129194)
  • Host folder shares unavailable in Hyper-V Linux VMs using Plan9 (resolved by KB5129194)
  • Remote Desktop Services may become unstable or unresponsive (resolved by KB5129194)
  • File History backup creation/updates may fail (resolved by KB5124006)

Disclaimer: We take measures to ensure that AI-generated content is of the highest possible quality, but we cannot guarantee its accuracy and recommend that users do their own independent research. Generated on 2026-10-12 01:30 PM

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