Forgotten Bootloaders Expose Secure Boot Blind Spot

Researchers discovered 11 vulnerable, but still trusted, UEFI shim bootloaders that could have been used to bypass Secure Boot on systems relying on Microsoft's third-party UEFI signing certificate. Despite being outdated and containing known flaws, these shims remained trusted components, allowing attackers to execute malicious code at boot time and establish persistent access. While Microsoft has revoked the vulnerable shims, patching legacy systems and addressing the ‘Secure Boot debt’ – the long-lived risk of outdated firmware – remains a significant challenge, particularly in complex enterprise environments.