Microsoft’s Secure Boot has been broken for a decade and no one noticed until now
| Source: Ars Technica AI
Tags: Secure Boot, UEFI, Microsoft, ESET, firmware security, bootkit, Linux security
ESET researchers found that 11 Microsoft-signed UEFI shim binaries — some from 2013 — were never revoked, letting any attacker with brief physical device access bypass Secure Boot entirely and install persistent bootkit malware that survives OS reinstalls on both Windows and Linux.
Details
Security firm ESET disclosed that Microsoft's Secure Boot has been trivially bypassable for 13 of its 14 years, due to Microsoft failing to revoke signed UEFI shim binaries after vulnerabilities were discovered in them. Researchers identified 11 such images — at least one from 2013 — that remain cryptographically trusted despite being known-defective.\n\nThe attack requires no novel exploit. An attacker with physical access installs one of these old, still-trusted shim binaries to bypass the entire Secure Boot chain, then loads bootkit malware that persists through OS reinstalls and hard drive replacements because it embeds in firmware rather than storage. ESET researcher Martin Smolár described the root cause as a key management failure, not a code vulnerability.\n\nBoth Windows and Linux devices are affected. Some of the shims came from Red Hat, OpenSUSE, and Oracle Linux; others from third-party utilities. Protections like SBAT and MOK deny lists didn't exist when many of these shims were signed, and Microsoft never retroactively added them to revocation lists.\n\nFor AI infrastructure teams running workloads on bare metal or UEFI edge hardware, persistent firmware compromise can undermine trust in the entire software stack including model serving environments. Patches depend on Microsoft updating its shim revocation list; until then, physical access controls are the primary mitigation.