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The September 2026 Windows security update is now available

From Microsoft 365 Message Center Archive by Merill Fernando · Microsoft may not have sent this notice to your tenant.
Windows
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What the notice says

Microsoft’s text, safely structured

The September 2026 security update is now available for all supported versions of Windows. We recommend that you install these updates promptly. For more information about the contents of this update, see the release notes, which are accessible from the Windows 11 update history page. To learn more about the different types of monthly quality updates, see Understanding Windows monthly updates.

Highlights for the Windows 11, version 25H2 update

  • This security update includes improvements that were part of update KB5120998 (released August 27, 2026).
  • This update expands high confidence device targeting data, increasing coverage of devices eligible to automatically receive new Secure Boot certificates. Devices receive the new certificates only after demonstrating sufficient successful update signals, maintaining a controlled and phased rollout.
  • This update makes quality improvements to the servicing stack, which is the component that installs Windows updates.

Short on time? Watch the Windows 11 release notes video for this month’s tips.

For instructions on how to install this update, see the KB article for your operating system listed below:

  • Windows 11, version 26H1: KB5124012
  • Windows 11, versions 25H2 and 24H2: KB5124008
  • Windows 11, version 23H2: KB5122880
  • Windows 11 Enterprise LTSC 2024: Baseline KB5124008
  • Windows 10, versions 22H2 and 21H2: KB5122878
  • Windows 10 Enterprise LTSC 2019 and Windows Server 2019: KB5122876
  • Windows 10 LTSB 2016 and Windows Server 2016: KB5123099
  • Windows Server 2025: KB5122871
  • Windows Server 2025 Datacenter: Azure Edition: Baseline KB5122871
  • Windows Server 2022: KB5122882
  • Windows Server 2022 Datacenter: Azure Edition: Baseline KB5122882
  • Windows Server 2012 R2: KB5123066
  • Windows Server 2012: KB5123065

Note: With recent and upcoming Windows updates over the next few months, a limited number of consumer and business devices might experience one additional restart during installation. This one‑time restart occurs after a Secure Boot certificate update is applied as part of the Secure Boot update process.

What changed

Between archive captures, newest first

The archive supplies one version of this notice.

Learn more

Links from the notice and their documentation checks

Shared KB KB5122871 (5 items)

Shared KB KB5124012

Not confirmed here

What this page cannot tell you
  • Whether your tenant is affected: this is Microsoft's notice, not a check of your settings.
  • 13 linked pages have not been read yet.
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