A faulty update was wreaking havoc with the boot process and also damaged files.

Microsoft has apparently fixed some buggy Windows 10 updates that they rolled out over the past month. These updates contained a defective version of chkdsk that damaged the file system on some PCs and made Windows fail to boot.

The updates that included the fault are KB4586853, which was issued on November 30, 2020. A second update, KB4592438, was released on December 8, 2020.

The chkdsk issue in Windows 10

The bug was first noted on a German blog called “Born’s Tech and Windows World” on December 18:

“In Windows 10 20H2 with installed cumulative update KB4592438, chkdsk causes massive issues. It destroys the file system during a disk check on SSDs, so Windows 10 can’t start after a reboot,”

“On some systems, the chkdsk c: /f command caused the Windows drive to become corrupted. The system was subsequently unable to boot after the file check, because the Windows drive was no longer found.”

Microsoft fixes the issue

The German blog that reported on the bug earlier has now confirmed that the fix is out. “It worked, the bug I reported about chkdsk ending in an unbootable Windows 10 2004/20H2 on some systems has been fixed,” he writes.

“Microsoft has now published an addendum in the support article for update KBkb4592438, which describes exactly this bug. There, Microsoft writes that on a smaller number of systems that have this update installed, running chkdsk /f can corrupt the file system and the device may fail to boot.”

Fixes for managed and unmanaged systems

Microsoft states that this issue is fixed and should be automatically prevented on unmanaged (via WSUS, SCCM, etc.) devices. However, it may take up to 24 hours for the fix to be applied to unmanaged devices. Microsoft states that the fix may be applied to the device faster if users restart Windows 10.

Managed devices in enterprise environments that have this update installed and are experiencing this issue, can be fixed by installing and configuring a special Group Policy. For more information on the use of Group Policy, Microsoft refers to the Group Policy Overview.

If there are devices that have already hit the issue, Microsoft has listed troubleshooting steps which it says should fix the problem.

Tip: Microsoft has lost its grip on the Windows 10 update process