Security readout for executives and security teams
Plain-English summary
Shim is the small UEFI Secure Boot loader used before the OS starts. This flaw can read past a buffer while validating SBAT metadata, potentially exposing sensitive boot-time data. The attacker needs local privileges, so urgency is measured: prioritize affected Red Hat boot infrastructure, especially shared, regulated, or high-trust systems.
Executive priority
Treat this as a moderate confidentiality risk, not an emergency remote compromise. Patch through normal security maintenance, with higher priority for sensitive systems, shared infrastructure, and environments where boot-time data exposure would be materially damaging.
Technical view
CVE-2023-40550 is a CWE-125 out-of-bounds read in shim verify_buffer_sbat(). Red Hat rates it medium with CVSS 3.1 score 5.5: local attack vector, low complexity, low privileges, no user interaction, high confidentiality impact, and no integrity or availability impact.
Likely exposure
Exposure is most likely on affected Red Hat Enterprise Linux 7, 8, 9, and named EUS/AUS/TUS/SAP streams using vulnerable shim, shim-signed, or shim-unsigned packages listed in the source bundle.
Exploitation context
The supplied sources do not show KEV listing or active exploitation. The CVSS vector indicates local access with low privileges is required. The stated impact is possible sensitive data exposure during boot, not remote code execution or service disruption.
Researcher notes
Evidence is strongest for Red Hat-packaged shim variants and listed RHEL streams. The bundle describes the bug class and impact but does not provide exploit details, proof of active exploitation, or broader non-Red Hat affected product data beyond the transferred Debian reference.
Mitigation direction
- Apply the relevant Red Hat RHSA shim updates for each affected RHEL stream.
- Prioritize systems using UEFI Secure Boot and affected shim-family packages.
- Check Red Hat CVE and errata pages for stream-specific package guidance.
- Include bootloader update handling in maintenance windows where operationally required.
Validation and detection
- Inventory RHEL 7, 8, 9, and named extended-support streams.
- Compare installed shim-family package versions with the affected versions in the source bundle.
- Confirm the applicable Red Hat security advisory is applied on each system.
- Track exceptions where vendor guidance or maintenance windows delay remediation.
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-2023-40550 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
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
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:L/UI:N/S:U/C:H/I:N/A:N1.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
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-2023-40550CVE reference · vdb-entry, x_refsource_REDHAT
- RHBZ#2259915CVE 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.