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CVE-2026-21265 is a Windows Secure Boot security feature bypass condition caused by the impending expiration of Microsoft Secure Boot certificates originally issued in 2011 and stored in UEFI trust databases, including KEK and DB. These certificates are used to validate updates to Secure Boot trust stores, third-party boot components, option ROMs, and the Windows Boot Manager. If affected systems do not receive updated replacement certificates, or if the operating system and firmware certificate update protection path fails because of firmware defects, Secure Boot trust updates may fail or behave unpredictably. This can disrupt the intended Secure Boot trust chain and undermine the mechanism that ensures boot components are signed by trusted authorities. The issue is therefore not a conventional memory-corruption flaw, but a trust-validation weakness tied to certificate lifecycle management and unreliable propagation of trust-anchor updates through firmware-dependent mechanisms.
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No public exploit code observed for this vulnerability.
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Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
25 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Windows Secure Boot certificate update/expiration issue labeled as a security feature bypass; primarily a reliability/maintainability security prerequisite with minimal direct attack vector described.
A Microsoft-reported critical zero-day vulnerability addressed in the January 2026 Patch Tuesday release; specific technical details are not provided in the content.
A Secure Boot security feature bypass related to expiring Secure Boot certificates, potentially undermining the trust mechanism for firmware modules.
An issue related to Secure Boot certificate expiration (certificates issued in 2011) that can cause systems to stop trusting new boot loaders or fail to receive future security updates if not updated in time; not described as immediate exploitation.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.