ShimApplication · Redhat
CVE-2023-40549
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 · uneditedAn out-of-bounds read flaw was found in Shim due to the lack of proper boundary verification during the load of a PE binary. This flaw allows an attacker to load a crafted PE binary, triggering the issue and crashing Shim, resulting in a denial of service.
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 confidenceShim bootloader contains an out-of-bounds read vulnerability due to missing boundary checks when loading PE (Portable Executable) binaries. An attacker can trigger the vulnerability by supplying a crafted PE binary, causing Shim to read beyond allocated memory boundaries and crash, resulting in denial of service.
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
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/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.
-
Identify installed Shim packageOn RPM-based systems (RHEL, Fedora), run: rpm -qa | grep -i shim-x64 or rpm -q shim-x64Affected if Shim package is installed on the system
-
Retrieve Shim versionRun: rpm -q --queryformat '%{VERSION}' shim-x64 (or the specific shim package name found)Affected if A version number is returned by the query
-
Compare version to affected rangeCompare the installed version number to 15.8 - versions less than 15.8 are affectedAffected if Installed version is less than 15.8 (for RHEL Shim packages)
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Check Fedora versionIf not using RHEL Shim package, run: cat /etc/fedora-release to verify if running Fedora 39Affected if System is running Fedora 39 with Shim installed
System is affected if Shim bootloader is installed and its version is below 15.8, or if running Fedora 39 with any Shim version.
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
Avoid loading untrusted or unverified PE binaries through Shim. Apply vendor-provided patches to Shim to add proper boundary validation during PE binary loading.
Shim version 15.8 or later
- Check current Shim version: rpm -q shim-x64 or rpm -qa | grep shim
- Update Shim package to version 15.8 or later: dnf update shim-x64 (Fedora) or yum update shim-x64 (RHEL)
- Verify the updated version: rpm -q shim-x64
- Reboot the system to ensure the new Shim binary is loaded
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Shim
Scoped from the published advisory
- Consultation2.0 h
- Implementation8.0 h
- Testing4.0 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 $4,480.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-40549 — 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-2023-40549 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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