A flaw in the Windows Boot Loader causes a security decision to rely on untrusted input, enabling an attacker with local authorization to bypass UEFI Secure Boot. The result is that unsigned firmware or boot components can be loaded, potentially compromising the integrity of the system’s startup process. The vulnerability does not provide additional remote access or data exposure beyond this local boot requirement.

Microsoft Windows 10 versions 1607, 1809, 21H2 and 22H2, as well as Windows Server 2016, 2019 and 2022—including Server Core installations—are affected by this flaw. These operating systems rely on UEFI firmware with Secure Boot enabled.

The CVSS base score of 6.7 indicates medium severity. Because the vulnerability requires the attacker to have local privilege to modify boot loader components or firmware, the attack vector is inferred to be local and practicable only when such access is available. No EPSS score is available and the vulnerability is not listed in the CISA KEV catalog, implying it is not currently exploited. Nevertheless, the ability to bypass a fundamental boot security mechanism warrants prompt remediation.