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VulnerabilityPublished Updated

CVE-2023-40547: Red Hat Enterprise Linux 7 · Out-of-bounds Write

Affects Red Hat Enterprise Linux 7Source CVE Database V5

0

Not known to be exploited · CVSS 8.3 High.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score
8.3High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
5.4% chance of exploitation in 30 days – higher than 92% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 25 Jan 2024

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

AI-suggested

  1. Secure the boot environment by restricting physical and network access to boot servers and infrastructure to prevent unauthorized interception or modification of boot traffic.
  2. Employ network-level protections such as strong encryption (e.g., HTTPS with validated certificates) and network segmentation to protect HTTP boot traffic from MitM attacks.
  3. Monitor and audit boot server configurations and logs for signs of compromise or unauthorized changes.
  4. Apply any available patches or updates from Red Hat addressing this vulnerability as soon as they are released.
  5. Consider upgrading to newer versions of Red Hat Enterprise Linux that may include improved secure boot mechanisms or mitigations.
  6. Implement hardware-based secure boot features and trusted platform modules (TPM) to enhance boot integrity verification.
  7. Use intrusion detection systems capable of monitoring early boot processes and network boot traffic anomalies.
  8. Educate system administrators on the risks of network booting and the importance of securing boot infrastructure.
  9. Regularly review and update incident response plans to include scenarios involving boot-level compromises.

Description

A remote code execution vulnerability was found in Shim. The Shim boot support trusts attacker-controlled values when parsing an HTTP response. This flaw allows an attacker to craft a specific malicious HTTP request, leading to a completely controlled out-of-bounds write primitive and complete system compromise. This flaw is only exploitable during the early boot phase, an attacker needs to perform a Man-in-the-Middle or compromise the boot server to be able to exploit this vulnerability successfully.

References

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