CVE-2021-3418
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIf certificates that signed grub are installed into db, grub can be booted directly. It will then boot any kernel without signature validation. The booted kernel will think it was booted in secureboot mode and will implement lockdown, yet it could have been tampered. This flaw is a reintroduction of CVE-2020-15705 and only affects grub2 versions prior to 2.06 and upstream and distributions using the shim_lock mechanism.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceThis vulnerability allows GRUB2 to boot directly without signature validation when certificates that signed GRUB are installed into the db. This bypasses the secure boot chain, allowing tampered kernels to boot while the kernel believes it's running in secureboot mode with lockdown active. Only affects GRUB2 versions prior to 2.06 using the shim_lock mechanism.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 2.06CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- High
- Privileges
- High
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed GRUB2 versionRun 'grub2-install --version' or 'grub-mkversion' to determine the installed GRUB2 version numberAffected if Version is less than 2.06
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Verify shim is in useCheck for shim EFI binaries in the EFI system partition, typically at /boot/efi/EFI/*/shim*.efi, and confirm shim_lock is loaded in GRUBAffected if Shim is present and shim_lock module is loaded
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Confirm secure boot is enabledRun 'mokutil --sb-state' to check if UEFI secure boot is activeAffected if Secure boot shows as enabled
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Inspect db UEFI variable for certificatesUse 'mokutil --list-enrolled' to list certificates enrolled in the UEFI db variable, or examine the db UEFI variable directly for any certificates that could sign GRUBAffected if Certificates exist in db that can validate GRUB directly without shim validation
System is affected if GRUB2 version is below 2.06, shim with shim_lock is in use, secure boot is enabled, AND certificates are enrolled in the db that could sign GRUB directly.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data2.06
Upgrade GRUB2 to version 2.06 or later and ensure the secure boot chain properly validates all components before execution. Review and remove any certificates from db that could enable direct GRUB booting.
- Consultation3.0 h
- Implementation6.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-3418 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-3418 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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