Microsoft says a September security update has broken File History backups for users across current versions of Windows 11 and for Windows 10 machines still receiving monthly patches through the Extended Security Updates program. The company disclosed the problem in its Knowledge Base support pages for the September 8 Patch Tuesday rollout. Affected users may be unable to create or run backups through File History.
The symptoms vary. Some users are told to reconnect their backup drive even when the drive is connected and working properly, according to Microsoft. The timestamp for the last backup may also fail to refresh. Files that were previously backed up without trouble can display an error saying no previous version is available.
The bug touches all current Windows 11 releases, including 26H1, 25H2, 24H2 and 23H2. Windows 10 is affected as well, because users registered for Extended Security Updates continue to receive monthly security updates. Users who suspect they have hit the problem can check the Windows Event Viewer for application crash events that reference FileHistory.exe or KERNELBASE.dll.
File History has been a fixture of Windows for years, offering a way to back up and restore important folders and files from a user account, including Documents, Music, Pictures, Videos and Desktop. Microsoft still technically supports the feature, but it treats File History as legacy and no longer develops it. Instead, the company steers users toward OneDrive or the Windows Backup program for backing up, syncing and recovering files.
For the newest Windows 11 releases, Microsoft has already shipped a fix. A preview update released Tuesday patches the bug so File History should work again. The update is optional, so users must install it themselves through Settings and Windows Update, where it appears as a 2026-09 Preview Update followed by a KB number.
The KB number depends on the Windows 11 edition. Users on Windows 11 26H1 will see KB5124006, while those on Windows 11 25H2 or 24H2 will find KB5124010. Clicking the Download & install link runs it. Although preview updates can be buggy, Microsoft offers no other option for now to those who depend on File History. Users who can wait will get the same fix in the October Patch Tuesday rollout.
Windows 11 23H2 and Windows 10 users have a longer wait. Microsoft no longer supports version 23H2, and Windows 10 is supported only through the ESU updates. The company says it is working on a fix for the issue and will release it in a future Windows update.
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