On Friday, Microsoft confirmed it has begun working on a security patch for a Defender zero-day vulnerability named "ShieldBreak." A security researcher who uses the "Nightmare Eclipse" handle disclosed this privilege escalation vulnerability after Microsoft released the August 2026 Patch Tuesday security updates. "Microsoft is aware of the reported vulnerability and is actively investigating the validity and potential applicability of these claims," a Microsoft spokesperson told BleepingComputer when asked for a statement regarding the new ShieldBreak zero-day. "Microsoft is committed to investigating security issues and updating impacted products to protect customers as soon as possible." Nightmare Eclipse described ShieldBreak as a bypass for RoguePlanet, another Defender privilege…