Security researcher Nightmare Eclipse has released a zero-day exploit named ShieldBreak that allows privilege escalation on Windows by targeting a vulnerability in Microsoft Defender. This exploit, designated as CVE-2026-50656, is categorized as a race condition vulnerability and affects the latest versions of Windows 11 and Windows Server 2025, with potential impacts on Windows 10. The exploit was disclosed on June 9, 2026, and Microsoft acknowledged the issue on June 16, rolling out fixes by July 9. The mechanics of ShieldBreak involve manipulating Defender’s scan path and executing a scheduled task to gain System-level privileges. Experts have noted differences between ShieldBreak and the previously known RoguePlanet exploit, emphasizing that ShieldBreak requires Defender to be active to function.