Microsoft BitLocker-protected drives can now be opened with just some files on a USB stick — YellowKey zero-day exploit demonstrates an apparent backdoor

There's nothing more dangerous than a bored engineer with a screwdriver, and hell hath no fury like a security researcher scorned. Last month, Security researcher Chaotic Eclipse (aka Nightmare-Eclipse) published two zero-day exploits, BlueHammer and RedSun, that made Windows Defender offer up system administrator privileges. They did this after their disclosure reports were allegedly dismissed by Microsoft's security team, resulting in a vendetta of sorts. Eclipse has now done it again, posting two new zero-day exploits, the first one an extremely serious BitLocker exploit named Yellow Key that grants full access to a locked drive. The second one, GreenPlasma, doesn't have a complete proof-of-concept (PoC), but it allegedly performs a local privilege escalation and gains system-level access. Given Eclipse's track record, it's a fair bet that it works as advertised.

YellowKey can be triggered simply by merely copying some files to a USB stick and rebooting to the Windows Recovery Environment. We tested this ourselves, and sure enough, not only does it work, it bears all the hallmarks of a backdoor, down to the exploit's files disappearing from the USB stick after it's used once.

The process is dead simple: grab any USB stick, get write access to the "System Volume Information," and copy into it the "FsTx" folder and its contents. Shift+click Restart to get Windows to the recovery environment, but then switch to holding down the Control key and don't let go. The machine will reboot, and without asking any questions or showing any menus, will drop you in an elevated command line with full access to the formerly Bitlocked drive, without asking for any keys.