As of October 8, 2026, the latest Windows 10 cumulative security update identified by Microsoft is KB5122878, released September 8, 2026. It lists OS builds 19045.7725 and 19044.7725 for the Windows 10 versions and servicing contexts Microsoft specifies. For a standalone download, open Microsoft’s KB5122878 release note and follow its link to the Microsoft Update Catalog; choose the package that matches your Windows version and system architecture.
Which Windows 10 update is the latest?
Microsoft’s September 8, 2026 release is KB5122878, with OS builds 19045.7725 and 19044.7725. The release note covers Windows 10 version 22H2 and version 21H2 under Windows 10 Extended Security Updates (ESU), as well as Windows 10 Enterprise LTSC 2021 and Windows 10 IoT Enterprise LTSC 2021. It is not a universal update for every historical Windows 10 release or edition. See Microsoft’s KB5122878 release note for the applicable products and details.
The previous monthly release was KB5120249, issued August 11, 2026, with builds 19045.7663 and 19044.7663. The newer September release is the one to look for if your system is eligible and has not already received a later applicable update. Microsoft’s August 2026 release note documents the preceding update.
How to download KB5122878 directly
Microsoft’s standalone package is provided through the Microsoft Update Catalog. The KB article links to the Catalog rather than identifying one universal download file: Catalog entries can differ by system architecture and servicing context, so select the result that matches the device.
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- Open the KB5122878 release note on Microsoft Support.
- Follow the Microsoft Update Catalog link in the article and search for KB5122878 if needed.
- Check the Catalog result’s product and architecture against the Windows version and system type installed on the target device before downloading.
- Run the downloaded package on the target device and follow the installer prompts. For organization-managed deployment, use the organization’s approved update channel and deployment process.
Do not rely on a third-party mirror or assume a static .msu link will work for every device. Microsoft’s KB page is the authoritative route to the available standalone package.
Choose between Windows Update and the Catalog
| Route | Best for | What to know |
|---|---|---|
| Windows Update | Most individual PCs that are offered the update | Windows downloads and installs it automatically when offered; no separate Catalog package selection is needed. |
| Microsoft Update Catalog | Manual download, one-off installation, or deployment scenarios requiring a standalone package | Use the link in Microsoft’s KB article and select the Catalog result appropriate to the device. |
| Windows Update for Business or WSUS | Organization-managed servicing | These are managed update channels, not the usual consumer download route. For WSUS, Microsoft’s release note specifies product and classification configuration. |
Microsoft notes: “If you installed earlier updates, only the new updates contained in this package will be downloaded and installed on your device.”
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Check applicability and servicing prerequisites
Before installing, confirm the Windows release and deployment context. The September release note identifies Windows 10 21H2 and 22H2 under ESU, along with Enterprise LTSC 2021 and IoT Enterprise LTSC 2021. It also says to use enablement package KB5015684 to move to Windows 10 version 22H2 where applicable.
Microsoft says the latest servicing stack update (SSU) must be installed. The page identifies SSU KB5122877, version 19041.7714, and describes the latest SSU as combined with the latest cumulative update. Some standalone or image-servicing deployments have additional prerequisites; these are not blanket requirements for every consumer PC:
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- Offline OS image servicing: Microsoft describes a prerequisite involving standalone SSU KB5031539 if the image does not include the July 25, 2023 LCU KB5028244 or a later LCU.
- WSUS or Catalog standalone installation: Microsoft describes a separate prerequisite involving standalone SSU KB5005260 if the device does not have the May 11, 2021 LCU KB5003173 or a later LCU.
Because these cases depend on how the image or device is serviced, check the prerequisite section of the official release note before deploying to an offline image or managed fleet.
Windows 10 support status
General support for Windows 10 version 22H2 ended October 14, 2025. Microsoft identifies Windows 10 ESU as the route for continued critical and important security updates, subject to the program’s applicability and supported editions; otherwise, it recommends moving to a later Windows version. The presence of KB5122878 in the release history does not mean every Windows 10 PC remains eligible for updates.
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Known issues reported for the September update
Remote Desktop Services instability
Microsoft reports that some organizations experienced Remote Desktop Services instability after the September security update. Symptoms included RDP connections failing after several minutes, sign-in problems, servers hanging during Remote Desktop Configuration, and related tools becoming unresponsive. Microsoft says updates released on or after September 14, 2026, including KB5129236, resolve this issue. The reported issue does not affect Windows 365 or Azure Virtual Desktop.
File History backups
Microsoft separately reports that some users may be unable to create or update File History backups after the September security update KB5124008. Affected users may see an erroneous “Reconnect your drive” message or fail to see the updated backup status. Microsoft’s page says it is working on a resolution in a future Windows update; this is a reported issue affecting some customers, not a universal outcome.
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