KB5123066: Overview with user sentiment and feedback

Overview

KB5123066 is the September 8, 2026 Monthly Rollup cumulative security update for Windows 8.1 and Windows Server 2012 R2. It bundles the August 2026 rollup's fixes plus new Secure Boot certificate device-targeting data. It requires the latest servicing stack update (KB5123499) to install.

General Purpose

• Adds higher-confidence device targeting data for automatic delivery of new Secure Boot certificates
• Includes the September 2026 security fixes (see Microsoft Security Update Guide)
• Requires SSU KB5123499 to be installed first; WSUS admins must approve both
• Includes boot.stl guidance for updating offline images and WinPE media

General Sentiment

Community discussion was not available in the provided data, so sentiment is based on Microsoft's own documentation. Two known issues are documented, and Microsoft has partially resolved one of them via an out-of-band update, so the update is not without problems.

Known Issues

• USB Audio Class 1.0 devices may fail with Code 10 or produce no audio; partially resolved by the September 14, 2026 OOB update (8-channel/3D audio fixed, other symptoms still open)
• Remote Desktop Services may become unstable, with RDP failures and hangs; resolved in updates released on or after September 14, 2026 (e.g., KB5129243)

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 2026-10-31 01:56 PM

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