Microsoft has confirmed that its September 2026 Windows security updates can prevent File History from creating or updating backups on some systems.
The regression places users who rely on the built-in feature at risk of assuming their files are protected when no recent backup has actually completed.
File History is a Windows backup capability accessed through Control Panel under System and Security. It periodically copies files to an external drive or network location and retains earlier versions, allowing users to recover documents that were accidentally changed, corrupted, or deleted.
September updates Break File History Backup
Microsoft added the problem to its known-issues documentation on September 19, following the September 8 security update rollout.
Affected computers may repeatedly show a “Reconnect your drive” warning even though a backup disk remains connected, accessible, and operational.
The File History interface may also retain an outdated “Last Backup” timestamp, while files that were previously protected can display “No previous version available.”
These indicators suggest the backup engine is not completing its expected operations rather than proving that the storage device itself has failed.
Administrators investigating the fault may find application-crash records in Windows Event Viewer that reference FileHistory.exe and KERNELBASE.dll.
Microsoft has not explained the underlying technical cause, and its advisory does not provide an official workaround. According to the advisory, Microsoft says it is developing a resolution for a future Windows update and will publish more information when available.
The issue affects Windows 11 versions 26H1, 25H2, 24H2, and 23H2, along with Windows 10 versions 22H2 and 21H2. Windows 10 Enterprise LTSC 2019 and LTSC 2016 are also listed as affected.
Microsoft says Windows Server platforms are not impacted. For Windows 11 24H2 and 25H2, the problem is documented with KB5124008, while the corresponding September security update for Windows 11 26H1 is KB5124012.
Users should verify backup status instead of treating the presence of a connected drive as confirmation of protection. Open Control Panel, select System and Security, choose File History, and inspect the most recent backup time.
Users can also open several important files through File History’s restore interface to confirm that recoverable versions exist. Event Viewer should be reviewed for crashes involving the two named components.
Although some users report that removing KB5124008 restores File History, uninstalling a security update can reopen vulnerabilities addressed by the patch and should not be treated as a low-risk fix.
Until Microsoft releases a correction, affected users should maintain a separate, verified backup using another trusted product or controlled manual copy process.
Organizations should monitor endpoint backup success, alert on stale timestamps, and test restoration rather than relying only on job status.
The incident reinforces a basic resilience rule: a backup is trustworthy only after you’ve independently validated its contents and recovery path.
Cut every SOC alert investigation by 21 min. Power your SOC with instant IOC context for immediate response: Integrate TI Lookup in your SOC
The post Microsoft Confirms September 2026 Windows Updates Break File History Backups appeared first on Cyber Security News.