Nightmare Eclipse, a security researcher, disclosed a new Windows vulnerability called ShieldBreak on August 12, 2026. The flaw can let an attacker elevate privileges from a low‑level user to full device control. Microsoft has not released a patch for ShieldBreak.

Eclipse has previously published several bugs affecting Microsoft products. In recent months the researcher has released details of multiple vulnerabilities, some of which were later exploited in the wild. The researcher faced a legal threat from Microsoft in early August after the company threatened to sue researchers who publish zero‑day details outside its disclosure process.

The vulnerability exploits a weakness in Windows Defender, the built‑in anti‑malware engine. A proof‑of‑concept app demonstrates the exploit; the user must run the app to trigger it. Security researcher Will Dormann confirmed that the exploit works when Windows Defender is enabled. ShieldBreak affects Windows 10, Windows 11 (including version 25H2), and Windows Server 2025, according to Eclipse. The earlier bug RoguePlanet was patched by Microsoft, but Eclipse said the fix was incomplete and the new exploit shows a bypass of that patch.

Microsoft said it is aware of the reported vulnerability and is investigating its validity. The company has not yet issued a patch. The disclosure occurred the day after Microsoft’s monthly Patch Tuesday, which addressed roughly 500 security issues, a number driven by the company’s use of AI to identify flaws.

The episode adds to a series of disputes between Eclipse and Microsoft over the handling of bug reports. Security experts continue to monitor the situation for a possible patch and for any attempts to weaponize the flaw.