dbcve.org
Grub2Application · Gnu

CVE-2022-28735

HIGH · 7.8 CVSS v3.1 Published 2023-07-20
Fix available
A fix is available. Upgrade to 2.06-3 or later.
See remediation →
80/100
Remediation priority · High
Zero-click

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 · unedited
The GRUB2's shim_lock verifier allows non-kernel files to be loaded on shim-powered secure boot systems. Allowing such files to be loaded may lead to unverified code and modules to be loaded in GRUB2 breaking the secure boot trust-chain.

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 · moderate confidence

The GRUB2 shim_lock verifier incorrectly allows non-kernel files to be loaded on systems with shim-powered secure boot enabled. This bypasses the secure boot trust chain by permitting unverified code and modules to execute in the bootloader environment, potentially allowing attackers to run malicious code before the OS loads.

MitigationApply vendor patches to shim and GRUB2 to enforce proper file type validation in the shim_lock verifier. Ensure secure boot configurations only allow loading of verified kernel files and signed GRUB2 modules.

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
Grub2Application
Affected:>= 2.00, < 2.06-3

CVSS 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
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/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 checks

Work through these to decide whether this CVE applies to you.

  1. Check GRUB2 version
    Run `grub2-install --version` or check your OS package manager for the installed grub2 or grub2-efi-x64 package version
    Affected if The installed version is greater than or equal to 2.00 and less than 2.06-3
  2. Verify secure boot is enabled with shim
    Run `mokutil --sb-state` to check if secure boot is active. Check for shim by examining the presence of shim-signed or shimx64 in /boot/efi/EFI/
    Affected if Secure boot is enabled and the shim bootloader is present in the EFI system partition
  3. Check shim_lock verifier configuration
    Inspect GRUB configuration files for shim_lock module loading. Check /boot/efi/EFI/*/grub.cfg for 'shim_lock' or examine if shim_lock.cfg exists. List available GRUB modules in /boot/efi/EFI/*/x86_64-efi/
    Affected if The shim_lock verifier is loaded or configured in the GRUB environment on a secure boot system

You are affected if GRUB2 version is between 2.00 and 2.06-2 (inclusive) AND secure boot with shim is enabled on your system, allowing the shim_lock verifier to incorrectly accept non-kernel files.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

dbcve · scoped
Upgrade available Upgrade to 2.06-3 or later
Fixed in 2.06-3
Interim mitigation

Apply vendor patches to shim and GRUB2 to enforce proper file type validation in the shim_lock verifier. Ensure secure boot configurations only allow loading of verified kernel files and signed GRUB2 modules.

Recommended fix High confidence

GRUB2 version 2.06-3 or later

  1. Identify the current GRUB2 version installed on the system using the package manager or running 'grub-install --version'
  2. Obtain GRUB2 version 2.06-3 or later from the distribution's package repository or upstream source
  3. Upgrade GRUB2 packages using the appropriate package manager for the distribution (e.g., apt, yum, dnf, zypper)
  4. Update the GRUB bootloader to ensure the new version is installed to the EFI system partition
  5. Reboot the system to verify the new GRUB2 version loads correctly
  6. Verify the shim_lock verifier is functioning properly and only allows kernel files to be loaded on shim-powered secure boot systems
Caveat Upgrading GRUB2 requires careful testing and may require re-enrollment of secure boot keys; ensure backup of current boot configuration before proceeding

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Grub2 Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,760
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $7,616.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2022-28735 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data