ShimApplication · Redhat
CVE-2023-40551
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 · uneditedA flaw was found in the MZ binary format in Shim. An out-of-bounds read may occur, leading to a crash or possible exposure of sensitive data during the system's boot phase.
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 confidenceA flaw in Shim's MZ binary format parser allows an out-of-bounds read during the boot process, potentially causing a denial of service (crash) or exposing sensitive memory contents. The MZ format is a legacy DOS/Windows executable format that Shim must parse when loading bootloaders.
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
ShimApplication
< 15.8
FedoraOperating system
= 39
Enterprise LinuxOperating system
= 8.0= 9.0CVSS 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
- High
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/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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Identify installed Shim packageRun 'rpm -qa | grep shim-x64' or 'rpm -qa | grep shim' to list installed Shim packagesAffected if Package version is found and is < 15.8 (Red Hat Shim), or system is Fedora 39, or system is RHEL 8.0 or 9.0 with unpatched Shim
-
Get precise Shim version numberRun 'rpm -q --qf '%{VERSION}-%{RELEASE} ' shim-x64' or check the shim package metadata directlyAffected if Version string shows a release earlier than 15.8
-
Verify shim binary in EFI system partitionCheck the active Shim binary used at boot: 'ls -la /boot/efi/EFI/*/shimx64.efi' and note the file modification date or version if embeddedAffected if The Shim binary in the EFI partition is the vulnerable version
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Confirm Secure Boot enrollment statusCheck if Shim is enrolled in UEFI/Secure Boot keys: 'mokutil --list-enrolled' or check UEFI firmware settingsAffected if Secure Boot is enabled and using the affected Shim, making boot-time exploitation possible
A system is affected if it runs any Shim version < 15.8 (Red Hat), or is Fedora 39, or is RHEL 8.0/9.0 with an unpatched Shim binary used in the boot process.
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.
dbcve · scoped15.8
Update Shim to a patched version that properly bounds-checks MZ format parsing. Given the boot-phase exploitation context, ensure secure boot configurations are reviewed and test boot process thoroughly after patching.
Shim version 15.8 or later
- Update your system package list: `dnf check-update` or `yum check-update`
- Install the updated shim package: `sudo dnf update shim-x64` or `sudo yum update shim-x64`
- Reboot the system to load the updated bootloader
- Verify the shim version is 15.8 or later: `rpm -q shim-x64`
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Shim
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing8.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,656.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-40551 — 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-2023-40551 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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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.
- 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
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