Microsoft has confirmed a zero-day privilege escalation vulnerability (CVE-2026-50656, internally tracked as RoguePlanet) in the Microsoft Malware Protection Engine, which underlies Microsoft Defender on virtually every Windows system. A public proof-of-concept exploit is available and no patch exists, meaning any local user or process on an affected Windows endpoint can escalate to SYSTEM-level access without additional prerequisites. The business risk is immediate and broad: compromised endpoints can lead to full system takeover, lateral movement, data exfiltration, and ransomware deployment across the enterprise.