"After installing the September 2026 Windows security update (the Originating KBs listed above), some customers using File History, might be unable to create or update backups," Microsoft said in a service alert seen by BleepingComputer.
Microsoft warns File History backups may fail after September 2026 updates
Microsoft has warned that the built-in File History backup feature in Windows may stop working on some systems after installing the September 2026 security updates. The company’s advisory—first spotted by Microsoft MVP Susan Bradley and reported by BleepingComputer—describes customers who cannot create or update File History backups following this month’s cumulative patches.
File History, accessible through Control Panel > System and Security > File History, is designed to back up the folders under a user’s account profile—Documents, Music, Pictures, Videos, and Desktop—to an external hard drive (for example, a USB flash drive) or to a network storage location such as a NAS.
Symptoms and technical indicators to watch for
Microsoft’s alert lists several symptoms reported on affected devices. Administrators and users may see application crash events in Event Viewer that reference FileHistory.exe and KERNELBASE.dll. Windows might incorrectly show “Reconnect your drive” messages even when compatible backup drives are connected and functioning.
Other visible signs include the “Last Backup” timestamp not updating and previously backed-up files presenting the status “No previous version available.” Those signals together point to File History failing to create or refresh backups after the September update.
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End the scrambleWhich Windows releases are affected
Microsoft identified the scope of impact explicitly. Affected Windows releases include Windows 10 21H2 or later, Windows 10 Enterprise LTSC 2016/2019, and Windows 11 23H2 and later. The advisory refers to the September 2026 cumulative updates as the triggering changes but does not, in the text BleepingComputer published, list the specific Originating KB numbers in-line.
How this fits into a wider set of September 2026 update problems
The File History warning arrives amid a broader set of issues tied to the September 2026 cumulative updates. Microsoft has already acknowledged multiple problems triggered by this month’s security updates and took emergency action: one week before the File History alert, Microsoft released out‑of‑band updates intended to fix Remote Desktop Services failures, Hyper‑V issues, and USB audio problems introduced by the September patches.
Microsoft also confirmed those emergency updates did not resolve all audio problems introduced by the September updates and said it is still working on a fix for the remaining audio issues. Separately, Microsoft published a temporary workaround for a bug that prevents some Windows 11 users from logging in with valid domain credentials after installing the September updates.
What this means for technologists, enterprises, and end users
- Technologists and security teams: Watch Event Viewer for crash events referencing FileHistory.exe and KERNELBASE.dll and verify backup integrity for systems running the affected Windows releases. The File History failure can leave end-user profiles without recent recoverable versions of files even when external or network drives appear connected.
- Enterprises and procurement leaders: Note the explicit list of impacted releases—Windows 10 21H2 or later, Windows 10 Enterprise LTSC 2016/2019, and Windows 11 23H2 and later—when assessing risk, remote backup strategies, and the need for additional mitigations beyond built-in File History.
- End users: Be alert to “Reconnect your drive” messages, a static “Last Backup” timestamp, or “No previous version available” statuses for files; those signs may indicate File History is not creating or updating backups after the September updates.
Microsoft’s public advisory confirms File History is among several post‑update disruptions this month but does not, in the reporting seen by BleepingComputer, provide a patch or a File History–specific workaround in that alert. Administrators and users who rely on File History for routine backups will want to confirm their recent restore points and alternative backup copies while monitoring Microsoft’s further advisories for any targeted fix or update.
