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CVE-2026-8863 is a UEFI Secure Boot security feature bypass affecting multiple legacy Microsoft-signed shim bootloaders, primarily shim version 0.9 and earlier. These first-stage bootloaders remain trusted on systems that accept Microsoft's third-party UEFI signing chain, allowing an attacker to introduce an old but still-trusted shim into the boot path and use it to load untrusted or vulnerable second-stage boot components before the operating system initializes. The weakness stems from outdated shim builds that do not enforce later boot-chain protections such as stronger revocation handling, Machine Owner Key denylist enforcement, and Secure Boot Advanced Targeting support, enabling a Bring Your Own Vulnerable Bootloader style attack against the UEFI trust chain. Successful exploitation occurs in the early boot phase, before normal operating system security controls are active, and can be used to defeat Secure Boot's intended code-signing guarantees.
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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.
15 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A vulnerability in old Microsoft-signed UEFI shim bootloaders that allows attackers to bypass UEFI Secure Boot by bringing their own vulnerable shim and executing untrusted code during boot.
A Secure Boot bypass issue involving old Microsoft-signed shim bootloaders (version 0.9 or below) that remain trusted on UEFI systems carrying the Microsoft third-party UEFI certificate, allowing attackers to introduce vulnerable first-stage loaders and undermine boot-chain protections.
A vulnerability designation covering old and forgotten Microsoft-signed UEFI shim bootloaders that can be abused to bypass UEFI Secure Boot and execute untrusted code during boot on systems trusting the Microsoft third-party UEFI certificate.
A Secure Boot bypass issue involving old, Microsoft-signed vulnerable shim bootloaders that remain trusted and can be abused to execute arbitrary code during boot and deploy UEFI bootkits or other malware.
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.