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ShimApplication · Redhat

CVE-2023-40548

HIGH · 7.4 CVSS v3.1 Published 2024-01-29
Fix available
A fix is available. Upgrade to 15.8 or later.
See remediation →
79/100
Remediation priority · High
No privileges 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
A buffer overflow was found in Shim in the 32-bit system. The overflow happens due to an addition operation involving a user-controlled value parsed from the PE binary being used by Shim. This value is further used for memory allocation operations, leading to a heap-based buffer overflow. This flaw causes memory corruption and can lead to a crash or data integrity issues during the 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 · moderate confidence

A heap-based buffer overflow vulnerability exists in Shim's 32-bit system where a user-controlled value parsed from a PE (Portable Executable) binary is used in an addition operation for memory allocation. The lack of proper bounds checking on this value allows an attacker to cause memory corruption, potentially leading to crashes or data integrity issues during the boot phase.

MitigationApply vendor-provided security updates for Shim immediately. Until patches are available, consider disabling Secure Boot or ensuring only trusted, verified PE binaries are executed during the boot process to reduce attack surface.

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
Affected:< 15.8= 15.8
FedoraOperating system
Affected:= 39

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

CVSS:3.1/AV:L/AC:H/PR:N/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 if Shim is installed on the system
    Locate Shim EFI binaries in /boot/efi/EFI/ or check via package manager (rpm -qa | grep shim)
    Affected if Shim is not present on the system - the vulnerability does not apply
  2. Identify the installed Shim version
    For RPM-based systems, run 'rpm -qa | grep shim' and note the version number; for direct file inspection, use 'strings shimx64.efi | grep -i version' or check file metadata
    Affected if The installed version is < 15.8 or = 15.8 for Red Hat builds, or version matches Fedora 39 builds
  3. Determine if 32-bit Shim binary is in use
    Look for 32-bit Shim binaries such as shimia32.efi, shim.efi.i386, or similar i386/x86 variants in the EFI boot directory; check if the system booted using a 32-bit Shim
    Affected if A 32-bit Shim binary (i386/x86) is being used - the vulnerability is specifically in the 32-bit system component
  4. Verify the system architecture and boot mode
    Check system architecture with 'uname -m' and review boot logs or EFI boot order for which Shim binary was loaded; 32-bit PE parsing occurs on x86 systems
    Affected if The system is x86/i386 architecture or boots using 32-bit Shim for any reason
  5. Confirm if Secure Boot is currently enabled
    Check Secure Boot status via 'mokutil --sb-state' or through system firmware/UEFI settings
    Affected if Secure Boot is disabled - while not required for exploitation, the vulnerability is triggered during boot phase when PE binaries are loaded

The system is affected if Shim is installed with version < 15.8 or = 15.8 (Red Hat) or matching the Fedora 39 build, AND the 32-bit Shim component (i386/x86) is in use on the system.

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 15.8 or later
Fixed in 15.8
Interim mitigation

Apply vendor-provided security updates for Shim immediately. Until patches are available, consider disabling Secure Boot or ensuring only trusted, verified PE binaries are executed during the boot process to reduce attack surface.

Recommended fix High confidence

Shim 15.8 or later

  1. Update the shim package to version 15.8 or later using your system's package manager (e.g., dnf update shim-x64 or dnf update shim-x86 for 32-bit systems)
  2. Verify the installed version matches the fixed release (15.8 or newer) using rpm -q shim or dpkg -l shim
  3. Reboot the system to ensure the updated shim is loaded during the next boot
  4. After reboot, confirm the system boots successfully and the shim version is correct
Caveat Upgrading bootloader components carries inherent risk; ensure you have a recovery mechanism in place before rebooting

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
  • 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-2023-40548 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