Microsoft Fixes Bug That Broke Windows File History Backup Feature

Microsoft Patches File History Backup Failure From September Updates

Microsoft has fixed a bug that broke the built-in File History backup feature on Windows systems following the rollout of its September 2026 security updates. In a service alert acknowledged by the company and first reported by BleepingComputer, Microsoft confirmed on September 22, 2026, that File History was failing to create or update backups on affected devices after installing this month's Patch Tuesday updates. The fix is now rolling out via optional cumulative updates for Windows 11, though Windows 10 machines running the same feature remain affected pending a further update.

Details

What Broke

Silent Backup Failures

On affected systems, File History stopped creating or updating backups to external drives and network locations without any clear error dialog. Users only noticed the problem when they went looking for a recent restore point and found none available.

Misleading Drive Prompts

Windows would incorrectly display a "Reconnect your drive" message even when a compatible backup drive was properly connected and functioning — a symptom that led many users to first suspect a hardware or cabling fault rather than a software regression from the update.

Stale Timestamps and Missing Versions

The "Last Backup" timestamp shown in the File History control panel stopped updating on impacted machines, and previously backed-up files began showing "No previous version available" when users tried to restore an earlier copy — even for files that had been successfully backed up before the update was installed.

Crash Signatures in Event Viewer

Microsoft and affected users confirmed the underlying failure through Event Viewer, where crash entries referencing FileHistory.exe and KERNELBASE.dll appeared on systems experiencing the bug, giving administrators a concrete way to identify affected endpoints.

How It Was Fixed

Microsoft's remediation played out over roughly two weeks:

1. September 8 — The September 2026 Patch Tuesday security updates ship, including KB5124008 for Windows 11 24H2/25H2, introducing the File History regression alongside fixes for a number of actively exploited vulnerabilities.
2. September 14 — An out-of-band update, KB5129195, ships to address a separate multichannel audio issue from the same update wave. It does not fix File History, and at least one user reported it reintroduced the bug even after they had manually removed KB5124008.
3. September 19 — Microsoft adds the File History failure to its official known-issues documentation, acknowledging the regression roughly a week and a half after the triggering update shipped.
4. September 22–23 — Microsoft ships the fix as part of this month's optional, preview cumulative updates: KB5124006 for Windows 11 26H1 and KB5124010 for Windows 11 24H2/25H2. Release notes state the update "addresses an issue where File History might fail to back up or restore files to an external drive or network location."

Because these are optional "C-week" preview updates, they do not install automatically through standard Windows Update. Devices that don't manually opt in will remain affected until the fix is folded into the mandatory October 13 Patch Tuesday release. No corresponding fix has been announced yet for the Windows 10 builds Microsoft listed as affected.

Some users on Microsoft's support forums found that uninstalling KB5124008 entirely restored File History functionality. Microsoft has not endorsed this as a supported workaround — the update also patched a substantial number of vulnerabilities, including actively exploited zero-days, so removing it trades a backup inconvenience for a meaningfully worse security posture.

Impact Assessment

Recommendations

For IT Administrators

• Push KB5124006/KB5124010 to managed Windows 11 fleets now via WSUS, Intune, or a manual optional-update rollout rather than waiting for the October mandatory release, particularly for endpoints that depend on File History for local recovery.
• Do not recommend uninstalling KB5124008 as a fix for end users — it removes protection against actively exploited vulnerabilities and should only be considered a last resort by informed security staff.
• Track Microsoft's release health dashboard for a Windows 10 fix. The September 22 rollout only covers Windows 11; Windows 10 21H2 and later, plus Enterprise LTSC 2016/2019, remain unaddressed as of this writing.
• Sweep Event Viewer logs across managed endpoints for FileHistory.exe crash events referencing KERNELBASE.dll to identify machines silently missing backups before assuming recovery points exist.

For End Users

• Check Settings > Windows Update > Advanced options > Optional updates and install KB5124006 (Windows 11 26H1) or KB5124010 (Windows 11 24H2/25H2) if it's offered for your build.
• After installing, manually trigger a backup via Control Panel > System and Security > File History and confirm the "Last Backup" timestamp actually updates.
• Don't dismiss a "Reconnect your drive" message as a loose cable or dead port — verify against this known issue first before troubleshooting hardware you may not need to touch.
• Avoid uninstalling KB5124008 to work around the problem; wait for the optional update or the October Patch Tuesday release instead, and consider a secondary backup method in the meantime for critical files.

Key Takeaways

1. Microsoft confirmed the September 2026 security updates, primarily KB5124008, broke File History backups on Windows 10 21H2 and later, Windows 10 Enterprise LTSC 2016/2019, and Windows 11 23H2 and later.
2. Symptoms included silent backup failures, misleading "Reconnect your drive" prompts, frozen "Last Backup" timestamps, and FileHistory.exe crashes referencing KERNELBASE.dll in Event Viewer.
3. Microsoft fixed the issue for Windows 11 via optional cumulative updates KB5124006 (26H1) and KB5124010 (24H2/25H2), released around September 22–23.
4. The fix is optional and must be manually installed through Windows Update; it becomes mandatory with the October 13 Patch Tuesday release.
5. No confirmed fix has been announced yet for the affected Windows 10 versions.
6. Uninstalling KB5124008 restores File History for some users but reopens the vulnerabilities — including actively exploited zero-days — that the update patched, and is not a recommended fix.

Sources

• Microsoft fixes bug that broke Windows File History backup feature — BleepingComputer