What is the BlueHammer vulnerability in Microsoft Defender?

BlueHammer is a flaw in Microsoft Defender, tracked as CVE-2026-33825, that allows for insufficient granularity of access control, enabling unauthorized users to elevate their privileges locally.

What is the deadline for federal agencies to patch BlueHammer?

Federal Civilian Executive Branch (FCEB) agencies must patch or discontinue use of the vulnerable software by May 6, 2026.

Who disclosed the BlueHammer vulnerability and why?

The BlueHammer vulnerability was disclosed in early April 2026 by a researcher named 'Chaotic Eclipse,' who was reportedly dissatisfied with Microsoft's vulnerability disclosure process.

Home / Technology / Researcher's Revenge: Microsoft Defender Flaws Exposed

Researcher's Revenge: Microsoft Defender Flaws Exposed

25 Apr

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Summary

Microsoft Defender flaw BlueHammer added to CISA's exploited list.
Federal agencies must patch by May 6 due to active exploitation.
Disgruntled researcher 'Chaotic Eclipse' disclosed multiple zero-days.

Researcher's Revenge: Microsoft Defender Flaws Exposed

The US Cybersecurity and Infrastructure Security Agency (CISA) has officially recognized BlueHammer, a critical flaw within Microsoft Defender, by adding it to its Known Exploited Vulnerabilities catalog. This action mandates that Federal Civilian Executive Branch (FCEB) agencies must address the vulnerability by May 6, 2026, or cease its use.

BlueHammer, tracked as CVE-2026-33825, allows unauthorized users to escalate privileges locally on affected systems. Its initial disclosure in early April 2026 came from security researcher 'Chaotic Eclipse,' who expressed dissatisfaction with Microsoft's vulnerability disclosure procedures. The researcher also subsequently revealed RedSun, another privilege escalation flaw, and unDefend, which can block Defender updates.