How To Mitigate The YellowHammer Microsoft BitLocker Zero-Day Vulnerability

It has been quite the week for Microsoft users when it comes to zero-day threat mitigation advice. Hot on the heels of the Microsoft recommendation to check the Exchange Emergency Mitigation Service if you use Exchange Server, as CVE-2026-42897 is confirmed as already under attack, comes fresh mitigation advice for Windows BitLocker users after the public release of security bypass exploit code by a researcher with a grudge about the way Microsoft Security Response Center responded to their vulnerability reports. That vulnerability, now tracked on the Common Vulnerabilities and Exposures database as CVE-2026-45585, and better known as YellowKey, could enable an attacker to gain access to BitLocker-protected storage using nothing more than a maliciously prepared USB key.

Organizations should treat this as an active threat, Neena Sharma, a cybersecurity specialist at Filigran, told me at the time, advising that, as immediate patching isn’t possible, they should implement “compensating controls like restricting USB boot access."

That patch is still not ready to roll out, but in the meantime, Microsoft has published mitigation advice given the likelihood that this will be targeted by attackers now that exploit code is known. In a May 19 advisory posting, the Microsoft Security Response Center said the “guidance that can be implemented to protect against this vulnerability until the security update is made available.”

The mitigations are, for the most part, likely outside the scope of most Windows consumers, and as such should only be attempted if you are sure of your abilities, have made backups and are willing to do so at your own risk. However, Microsoft said that you can add a PIN to your BitLocker protection to prevent exploitation, and the various methods for doing so are included in the published advisory. Given that YellowKey has yet to be exploited in the wild, and that successful exploitation requires physical access to your machine, I would suggest that, for most users, it will make sense to either wait for the security update to roll out or, if your risk profile demands it, add that PIN. Full mitigation instructions, including all necessary command-line codes, are included in the advisory.