A security researcher has disclosed details of a newly discovered Windows vulnerability that could enable attackers to take complete control of a computer, shortly after Microsoft released its latest monthly security updates. The flaw, called ShieldBreak, affects Microsoft Defender, the security software built into Windows.
Researcher Nightmare Eclipse has published a proof-of-concept exploit demonstrating how the vulnerability could be used to escalate privileges from a low-privileged user account to SYSTEM-level access, potentially giving an attacker broad control over the affected device and its data, according to security reports.
The exploit has reportedly been tested on Windows 11 version 25H2 and Windows Server 2025. Nightmare Eclipse said that Windows 10 and other supported Windows Server editions are also vulnerable, although the published proof-of-concept was not tested on those platforms. Security researcher Will Dormann independently verified the reported behaviour and noted that Microsoft Defender must be enabled for the exploit to function.
ShieldBreak is drawing particular attention because it is described as a bypass for Microsoft’s earlier fix for another Defender vulnerability known as RoguePlanet (tracked as CVE-2026-50656), which was addressed in Microsoft’s July security updates. Nightmare Eclipse claims the new exploit can circumvent that patch. Microsoft has not yet released a dedicated security update for ShieldBreak.
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