There’s a vulnerability in Microsoft’s handling of NTFS filesystem images that was discovered by Marius Tivadar, a security researcher at Bitdefender. To exploit the vulnerability, the Romanian hardware expert just published proof-of-code on GitHub that will result in crashing most computers running Windows even when they are in a locked state.

Windows machines crash in a few seconds because of the autoplay feature

Tivadar’s proof-of-concept includes a malformed NTFS image that you can place on a USB thumb drive. If you insert the USB drive in a Windows computer, it will crash in a few seconds displaying the BSOD. “Auto-play is activated by default,” Tivadar detailed in a PDF document.

Even with auto-play [is] disabled, [the] system will crash when the file is accessed. This can be done for [example,] when Windows Defender scans the USB stick, or any other tool opening it.

Locked PCs running Windows also crash

The worst thing about the bug is the fact that it can crash even locked PCs. In other words, PCs crash even when they should not read data from USB drives.

I strongly believe that this behavior should be changed, [and] no USB stick/volume should be mounted when the system is locked,” Tivadar said. “Generally speaking, no driver should be loaded, no code should get executed when the system is locked and external peripherals are inserted into the machine.

Microsoft couldn’t care less

Tivadar contacted the tech giant last year, but he decided to publish the code today because the company declined to categorize the issue as a security bug. Microsoft even downgraded the severity of the bug saying that the exploit required physical access or social engineering that would trick the user.

Hey Marius, Your report requires either physical access or social engineering, and as such, does not meet the bar for servicing down-level (issuing a security patch). […] Your attempt to responsibly disclose a potential security issue is appreciated and we hope you continue to do so.

Tivadar said that you don’t even need physical access because the bug can be deployed via malware.

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