The File History backup bug introduced by Microsoft’s September 2026 security updates is breaking backups on a wide range of Windows 10 and Windows 11 devices, with affected users reporting crash events, stale timestamps, and misleading error messages. Microsoft has issued a service alert acknowledging the problem, which spans eight distinct Windows releases.
File History, introduced back in Windows 8, automatically saves copies of files in a user’s profile folders (Documents, Music, Pictures, Videos and Desktop) to an external drive or a network location. It is distinct from the newer Windows Backup, which pushes data to OneDrive. On affected systems, the feature fails silently or noisily, depending on which symptom manifests first.
What the File History Backup Bug Actually Looks Like
The symptoms are varied enough to cause real confusion. Affected devices may show application crash events in Event Viewer referencing FileHistory.exe and KERNELBASE.dll. Windows may also display a ‘Reconnect your drive’ message even when a compatible backup drive is connected and functioning correctly, a particularly frustrating red herring for anyone who spends time unplugging and re-plugging hardware looking for a fault that isn’t there.
Beyond the misleading prompt, users may find that the ‘Last Backup’ timestamp simply stops updating, and previously backed-up files report ‘No previous version available.’ That last symptom is the one most likely to sting at the worst possible moment, when someone actually needs to recover a file.
In its service alert, first spotted by Microsoft MVP Susan Bradley and seen by BleepingComputer, Microsoft confirmed the scope of the problem: ‘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.’
Affected Windows Versions and the Fix
The File History backup bug affects a broad range of releases. On the Windows 11 side, versions 23H2, 24H2, 25H2 and 26H1 are all in scope. Windows 10 is equally exposed, with version 22H2, version 21H2, Enterprise LTSC 2019 and Enterprise LTSC 2016 all listed as affected. The originating updates include KB5124012 for Windows 11 26H1, KB5124008 for 25H2 and 24H2, KB5122880 for 23H2, KB5122878 for Windows 10 22H2 and 21H2, KB5122876 for LTSC 2019 and KB5123099 for LTSC 2016.
One group not affected: according to Notebookcheck, Windows Server editions are not touched by this particular bug, which will at least spare administrators a separate class of headache.
As for the fix, Tech Insider reports that Microsoft has confirmed a resolution, with the problem addressed in updates released on and after 22 September 2026, including KB5124010. Tech Insider also notes that BleepingComputer first reported the File History outage on 21 September 2026. Separately, Senserva indicates the issue is resolved in updates released on and after 14 September 2026, such as KB5129236, a discrepancy in dates between the two sources that Microsoft’s own documentation will need to settle for anyone tracking the precise remediation timeline.
The practical upshot: if you are running an affected version and have not yet applied a post-September 14 or post-September 22 cumulative update, File History may be silently failing. Worth checking before you need it.
A Busy Month for September 2026 Patch Problems
The File History issue is far from the only fallout from this month’s cumulative updates. One week before the File History alert, Microsoft released out-of-band updates to address Remote Desktop Services failures, Hyper-V issues and USB audio problems, all traced back to the same September 2026 security release. Microsoft subsequently confirmed those emergency updates did not resolve all the audio problems, and that work on the remaining audio fix was still ongoing.
A separate bug also surfaced preventing some Windows 11 users from logging in with valid domain credentials after installing the September updates, for which Microsoft shared a temporary workaround while a proper patch is prepared.
For affected users, the priority is straightforward: install the confirmed fix updates (particularly KB5124010) and verify that File History resumes creating backups as expected. Access is through Control Panel, under System and Security, then File History.
