Windows Secure Boot Certificate Update Security Feature Bypass

CVE-2026-21265 is a security feature bypass vulnerability affecting Microsoft Windows Secure Boot. The issue arises from the handling of Secure Boot certificates originally issued in 2011 that are approaching expiration in 2026. Windows relies on these certificates to validate boot components through UEFI Secure Boot. If certificate updates are not applied correctly, Secure Boot may fail to enforce trust validation consistently. A local attacker with administrative privileges could exploit this condition to weaken Secure Boot protections, potentially allowing untrusted boot components to execute. This vulnerability does not allow remote exploitation and requires local, high-privilege access.