Vulnerable UEFI Shim Bootloaders Risk Broad Secure Boot Bypass

**Executive summary:** Security researchers identified critical vulnerabilities in older versions of the open-source UEFI shim bootloader (notably versions 0.9 and earlier) that allow attackers to bypass Secure Boot using BYOVD-style techniques, enabling arbitrary code execution during early boot, persistent compromise that can survive reboots and OS reinstalls, and broad supply-chain exposure across multiple vendors; Microsoft recommends deploying DBX revocations while administrators must test updates carefully to avoid unintentionally bricking systems.