Old Microsoft-signed UEFI shims may bypass Secure Boot

Colleagues, I’d like to flag a cybersecurity development. Researchers have identified 11 legacy Microsoft-signed UEFI shims that may be used to bypass Secure Boot.

The scenario is concerning because malicious code can execute before the operating system loads. This creates a pathway for UEFI bootkits and stealthy persistence.

Microsoft revoked the vulnerable bootloaders in the June 2026 Patch Tuesday update, but the risk remains wherever outdated or non-revoked components are still in use.

Why it matters: securing the boot chain is not a formality — it is a foundational security layer.

Are you checking the freshness of your boot components and revocation lists?