The September 2026 Windows security updates introduced a known issue affecting the File History backup feature on Windows 10 (21H2 and later, Enterprise LTSC 2016/2019) and Windows 11 (23H2 and later). The bug caused File History to fail backing up or restoring files, triggered application crashes referencing FileHistory.exe and KERNELBASE.dll, and generated erroneous 'Reconnect your drive' alerts. Microsoft acknowledged the problem and released fixes in optional cumulative updates KB5124006 and KB5124010 for Windows 11 26H1 and 24H2/25H2, respectively. The fix will also be included in the October 13, 2026 Patch Tuesday updates. This issue is not a security vulnerability but a functional bug impacting backup reliability.

Users of affected Windows versions experienced failure of the File History backup feature, preventing creation or updating of backups to external or network drives. This could lead to loss of backup data continuity and inability to restore previous file versions. The issue caused application crashes and misleading system alerts, potentially disrupting user workflows dependent on File History backups. There is no indication of security compromise or exploitation; the impact is limited to backup functionality degradation.

Microsoft has released optional cumulative updates (KB5124006 and KB5124010) for Windows 11 versions 26H1 and 24H2/25H2 that resolve the File History backup issue. Users are recommended to install these updates to restore backup functionality. For users who do not install the optional updates, the fix will be included in the October 13, 2026 Patch Tuesday updates. No additional action is required beyond applying these updates. This is a functional bug fix, not a security vulnerability requiring emergency response.