Security readout for executives and security teams
Plain-English summary
CVE-2023-40551 is a bootloader-chain issue in Shim, used by affected Red Hat Enterprise Linux systems during Secure Boot. A malformed MZ binary can cause an out-of-bounds read, potentially crashing the boot phase or exposing limited sensitive data.
Executive priority
Treat this as a scheduled but important infrastructure update. It is not evidenced as internet-scale active exploitation, but it affects the boot chain, where failures can cause outages and recovery complexity.
Technical view
The flaw is CWE-125 in Shim MZ binary parsing. CVSS is 5.1 with local attack vector, low complexity, high privileges, no user interaction, low confidentiality impact, and high availability impact. Red Hat lists affected shim, shim-signed, and shim-unsigned packages across RHEL 7, 8, and 9 streams.
Likely exposure
Exposure is most relevant on affected Red Hat Enterprise Linux systems using the listed Shim packages, especially Secure Boot-enabled fleets and long-lived EUS, AUS, TUS, SAP, or mission-critical streams.
Exploitation context
The provided sources do not show CISA KEV listing or active exploitation. The CVSS vector indicates local access with high privileges is required, limiting broad remote attack likelihood but making boot integrity and recovery planning important.
Researcher notes
Evidence supports an out-of-bounds read during MZ parsing in Shim. The affected data is specific to Red Hat package streams listed in the bundle. Public sources here do not provide exploit details or a universal non-update workaround.
Mitigation direction
- Review the matching Red Hat advisory for your RHEL stream.
- Apply vendor-provided shim updates through approved maintenance channels.
- Prioritize Secure Boot-enabled and operationally critical systems.
- Check Red Hat guidance before changing bootloader or Secure Boot configuration.
- Plan rollback and recovery procedures for boot-chain updates.
Validation and detection
- Inventory RHEL versions and installed shim-related packages.
- Compare package names and versions against the affected list.
- Confirm the applicable RHSA update is installed.
- Validate Secure Boot systems reboot successfully after maintenance.
- Record exceptions for unsupported or extended support streams.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-125: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2023-40551 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H0.84.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.1MediumVector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- RHSA-2024:1834CVE reference · vendor-advisory, x_refsource_REDHAT
- RHSA-2024:1835CVE reference · vendor-advisory, x_refsource_REDHAT
- RHSA-2024:1873CVE reference · vendor-advisory, x_refsource_REDHAT
- RHSA-2024:1876CVE reference · vendor-advisory, x_refsource_REDHAT
- RHSA-2024:1883CVE reference · vendor-advisory, x_refsource_REDHAT
- RHSA-2024:1902CVE reference · vendor-advisory, x_refsource_REDHAT
- RHSA-2024:1903CVE reference · vendor-advisory, x_refsource_REDHAT
- RHSA-2024:1959CVE reference · vendor-advisory, x_refsource_REDHAT
- RHSA-2024:2086CVE reference · vendor-advisory, x_refsource_REDHAT
- https://access.redhat.com/security/cve/CVE-2023-40551CVE reference · vdb-entry, x_refsource_REDHAT
- RHBZ#2259918CVE reference · issue-tracking, x_refsource_REDHAT
- https://lists.debian.org/debian-lts-announce/2024/05/msg00009.htmlCVE reference · x_transferred
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Out-of-bounds Read
Out-of-bounds Read represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.