Cybersecurity researchers report that attackers may be able to bypass UEFI Secure Boot by abusing old, Microsoft-signed “shims”—first-stage boot loaders intended to allow Linux and other boot tools to operate under Secure Boot. One report says researchers identified 11 Microsoft-signed shim applications that could be vulnerable on systems that use the modern UEFI firmware standard. If exploited, an attacker can execute untrusted code during the system’s boot process, potentially enabling malicious UEFI bootkits or other malware.
A second outlet adds that the full scope of affected systems is uncertain because there is no definitive public inventory of how many older shim versions remain deployed across UEFI devices. It also cites ESET’s findings that vulnerable versions correspond to shim releases at version 0.9 or below. According to that report, Microsoft has revoked the problematic shim certificates/versions, with the revocations occurring in June. The reports collectively emphasize that Secure Boot is designed to prevent unauthorized boot code, but these particular signed components may allow a path around that protection when present in vulnerable, older forms.
