GoKawiilMicrosoft has shared mitigations for YellowKey, a recently disclosed Windows BitLocker zero-day vulnerability that grants access to protected drives.
The security flaw was disclosed last week by an anonymous security researcher known as 'Nightmare Eclipse,' who described it as a backdoor and published a proof-of-concept (PoC) exploit.
Nightmare Eclipse said that exploiting this zero-day involves placing specially crafted 'FsTx' files on a USB drive or EFI partition, rebooting into WinRE, and then triggering a shell with unrestricted access to the BitLocker-protected storage volume by holding down the CTRL key.
Last month, they also disclosed the BlueHammer (CVE-2026-33825) and RedSun (no identifier) local privilege escalation (LPE) zero-day flaws, both of which are now being exploited in attacks.
The researcher also leaked GreenPlasma, a zero-day privilege-escalation security issue that attackers can abuse to obtain a SYSTEM shell, and UnDefend, another zero-day that attackers with standard user permissions can exploit to block Microsoft Defender definition updates.
While the exact circumstances that triggered this spree of exploit leaks are still unclear, Nightmare Eclipse previously said that these disclosures are in protest of how Microsoft's Security Response Center (MSRC) handled the disclosure process for other security flaws they reported in the past.
Microsoft shares YellowKey mitigations
On Tuesday, Microsoft said it is now tracking the YellowKey flaw under CVE-2026-45585 and shared mitigation measures to defend against potential attacks exploiting it in the wild.
"Microsoft is aware of a security feature bypass vulnerability in Windows publicly referred to as "YellowKey". The proof of concept for this vulnerability has been made public violating coordinated vulnerability best practices," Microsoft said in a Tuesday advisory.
"We are issuing this CVE to provide mitigation guidance that can be implemented to protect against this vulnerability until the security update is made available."
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