A Windows 10 update rolled out by Microsoft contained a buggy 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 and KB4592438. Microsoft’s notes on these updates now incorporate a warning: “A small number of devices that have installed this update have reported that when running chkdsk /f, their file system might get damaged and the device might not boot.”
The notes further reveal: “This issue is resolved and should now be prevented automatically on non-managed devices,” meaning PCs that are not enterprise-managed. On managed PCs Microsoft recommended a group policy setting that rolls back the faulty update. If there are devices that have already hit the issue, Microsoft has listed troubleshooting steps which it says should fix the problem.
The chkdsk utility itself is not listed in the files that are patched by these updates, suggesting that the problem is with other system files called by chkdsk.