Microsoft has shipped a fix for the Windows File History backup bug that left users on multiple Windows 10 and Windows 11 versions unable to create or update backups after installing September 2026 security updates. The fix arrived quietly, but the underlying problem had already caused enough noise in Event Viewer and enough confusion over phantom drive errors to warrant its own service alert.
What the File History backup bug actually does
File History, accessible via Control Panel under System and Security, backs up a user’s account profile (Documents, Music, Pictures, Videos and Desktop) to an external drive or network location, then lets them retrieve older versions of files from hours, days or weeks back. After the September Patch Tuesday updates landed, the feature started misbehaving in several overlapping ways on affected machines.
On impacted systems, File History was triggering application crash events in Event Viewer referencing FileHistory.exe and KERNELBASE.dll. Backed-up files showed ‘No previous version available’, and the ‘Last Backup’ timestamp stopped updating. According to Microsoft Support, affected devices were also incorrectly displaying a ‘Reconnect your drive’ message even when a compatible backup drive was connected and working properly, a particularly disorienting symptom, since it pointed users towards a hardware problem that did not exist.
‘After installing the September 2026 Windows security update, some customers using File History might be unable to create or update backups,’ Microsoft said in a Saturday service alert seen by BleepingComputer.
The affected versions span a wide slice of the installed base: Windows 10 21H2 or later, Windows 10 Enterprise LTSC 2016 and 2019, and Windows 11 23H2 and later.
Which updates carry the Windows File History backup fix
PCWorld confirmed that the bug traces specifically to KB5124008 and KB5122878, the Windows 11 and Windows 10 September security updates respectively. Microsoft has now resolved the Windows File History backup bug for Windows 11 customers through two optional cumulative updates: KB5124006 for devices running Windows 11 26H1, and KB5124010 for those on Windows 11 24H2 and 25H2.
‘This update addresses an issue where File History might fail to back up or restore files to an external drive or network location,’ Microsoft said. ‘We recommend you install the latest update for your device as it contains important improvements and issue resolutions, including this one.’
Users who prefer to skip optional updates (or who simply do not want to install a preview build) will receive the fix automatically with next month’s Patch Tuesday rollout on October 13.
It is worth noting that Windows 10 users are not yet covered by the optional fix. Microsoft’s announcement on Tuesday addressed Windows 11 customers specifically, which means Windows 10 machines remain exposed until the October Patch Tuesday updates arrive.
Part of a broader September update headache
The File History fix is one of several remediation efforts Microsoft has had to mount in the wake of this month’s Patch Tuesday. A week ago, out-of-band updates went out to address Hyper-V problems, Remote Desktop Services failures and USB audio issues, all triggered by the same September security update batch. Days after that, Microsoft shared a temporary workaround for a separate bug preventing some Windows 11 users from logging in with valid domain credentials after installing the same updates.
For anyone running the affected Windows File History backup feature and wanting the fix today rather than waiting until 13 October, the optional cumulative updates are available through Windows Update now.
