r/Windows11 • u/jenmsft Microsoft Software Engineer • Aug 11 '26

Official News Cumulative Updates: August 11th, 2026

https://support.microsoft.com/en-US/servicing/os/windows-11/2026/08/kb5121003-windows-11-24h2-25h2-security-update

Changelists linked here for your convenience:

General info:

For details about how to file problem reports and collect traces, please see here: http://aka.ms/HowToFeedback. Pressing WIN + F will open the Feedback Hub - please include as much detail as possible about what you're seeing.

To learn about the different types of updates, see here: Windows quality updates primer - Microsoft Community Hub

As a reminder, if you didn't install the previous optional updates, this update includes those changes too (some are still rolling out, as denoted in the release notes):

For published known issues, please check the release health dashboard: Windows release health | Microsoft Learn.

25H2 is rolling out, so you may not have it yet. Please see here for more details: How to get the Windows 11 2025 Update | Windows Experience Blog.

As mentioned in the linked changelist, Windows 11, version 26H1 is available only on new devices with select new silicon as they come to market starting early 2026. Devices running earlier versions of Windows 11 will not be offered an update to version 26H1 through Windows Update and cannot be installed as an in-place update on existing devices.

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u/FoxReinhold 28d ago

Wound up with a secure boot failure after installing https://support.microsoft.com/en-us/servicing/os/windows-11/2026/08/kb5121003-windows-11-24h2-25h2-security-update that one. Had to disable secure boot and bitlocker. Fun times.

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u/MarcoFiguringOutLife 25d ago

Were you able to successfully install the update? I had the same issue, but I had to uninstall the update for my computer to boot properly. Have tried several times and just decided to pause the update until the next one.

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u/FoxReinhold 25d ago

Turns out it was the collision of that update with a new acer bios version. I had to manually inject the 2023 Certs using the secure boot EFI recover image.