A security researcher known as Nightmare Eclipse has released a new Microsoft Defender zero-day exploit named "ShieldBreak" after Microsoft released the August 2026 Patch Tuesday security updates. The new vulnerability is described as a bypass for RoguePlanet, another Defender privilege escalation flaw disclosed in June and patched by Microsoft one month later. However, cybersecurity expert Kevin Beaumont, who also published ShieldBreak exploitation detection queries for Microsoft Defender for Endpoint, said that the two exploits work very differently. "RoguePlanet was a filesystem race condition vuln that uses virtual disks and NT native file manipulation to trick quarantine process into overwriting system files," Beaumont noted. "ShieldBreak user-mode callback hook to change file…