After Microsoft threatened legal action, a security researcher publishes a new Windows zero-day bug

A security researcher published details and a proof-of-concept for a zero-day vulnerability dubbed "ShieldBreak" in Windows Defender that enables escalation to full system access on Windows 10, Windows 11 (25H2) and Windows Server 2025; the exploit is released as a Windows app that requires user execution, Microsoft has not yet patched the issue, and the disclosure follows a contentious history between the researcher and Microsoft over prior bug reports.