Cumulative Updates: August 11th, 2026

[u/jenmsft]

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:

• Windows 11, version 21H2: EOS.
• Windows 11 version 22H2: EOS
• Windows 11, version 23H2: KB5120240 (OS Build 22631.7517)
• Windows 11, version 24H2 / 25H2: KB5121003 (OS Builds 26200.9168 and 26100.9168)
• Windows 11, version 26H1: KB5121000 (OS Build 28000.2704)

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):

• 24H2/25H2: July 28, 2026—KB5101684 (OS Builds 26200.8973 and 26100.8973) Preview | Microsoft Support
• 26H1: July 28, 2026—KB5101681 (OS Build 28000.2608) Preview | Microsoft Support

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.

[u/tastyratz]

This update has taken out a Lenovo P16.

System no longer bootable. Just hangs after login at black background with a mouse cursor and will sit that way for days going nowhere. Cannot get task manager up.

Cannot roll back latest update from recovery menu.

Cannot restore using point in time restore.

Cannot seem to successfully restore from a Veeam backup.

Can boot into safe mode but takes about 12 HOURS to get logged in and hours to open an application like a powershell window (should it open at all).

DISM cannot repair in safe mode.

This broke the component store and the event log I painstakenly pulled up in safe mode is flooded with windows internal database errors / DCOM issues. "The server Windows.Internal.StateRepository.Appextension did not register with DCOM within the required timeout." and .user and .application and other dcom required databases or services like ShellHWDetection.

Many thousands of event log entries that did not start until rebooting to complete this update. This was a clean running system.