Chaotic Eclipse, a security researcher, has revealed a proof-of-concept (PoC) for a new vulnerability called ShieldBreak, which is a zero-day flaw in Microsoft Defender that bypasses the patch for the previously identified CVE-2026-50656 (RoguePlanet). This vulnerability could allow attackers to execute code at the SYSTEM level on affected Windows systems. Chaotic Eclipse tested the PoC on the latest versions of Windows 11 and Windows Server 2025, achieving a 100% success rate. Windows 10 and its server editions are not supported by the PoC but remain vulnerable. Microsoft had issued security updates for RoguePlanet, which has a CVSS score of 7.8, affecting the Malware Protection Engine and representing a local privilege escalation issue. Chaotic Eclipse has previously disclosed two other zero-day vulnerabilities, YellowKey and GreenPlasma, which affect BitLocker and the Windows Collaborative Translation Framework, respectively. Microsoft criticized the public disclosure of these vulnerabilities as irresponsible and emphasized the importance of Coordinated Vulnerability Disclosure.