Three vulnerabilities in Microsoft Defender, known as BlueHammer (CVE-2026-33825), RedSun, and UnDefend, are being actively exploited by hackers. BlueHammer has been patched, while RedSun and UnDefend remain unpatched. The public release of exploit code has accelerated real-world attacks, affecting Windows 10, Windows 11, and Windows Server systems. Attackers have begun exploiting these vulnerabilities, leading to concerns about privilege escalation, disruption of security updates, and the rapid spread of attacks.