Nightmare Eclipse has released a new Microsoft Defender zero-day exploit named "ShieldBreak" after Microsoft released the August 2026 Patch Tuesday security updates.

The PoC posted by Nightmare Eclipse, who has been feuding with Microsoft for months, grants an attacker system-level privileges once they gain any access.

ShieldBreak is a claimed patch bypass for Defender flaw CVE-2026-50656, with a PoC tested on Windows 11 25H2 and Server 2025.