CVE-2023-40547
HIGHEPSS 92th pctlDescription
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.
How to fix
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Exploit Intelligence
High risk: more likely to be exploited than 92% of all known CVEs.
References
Related Vulnerabilities
Other CWE-787 (Out-of-bounds Write) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2025-22457 | Critical | 9.0 | 100% | KEV + Ransom | Fix |
| CVE-2025-0282 | Critical | 9.0 | 100% | KEV + Ransom | - |
| CVE-2023-4863 | High | 8.8 | 100% | KEV | Fix |
| CVE-2015-3113 | Critical | 9.8 | 100% | KEV | Fix |
| CVE-2021-20038 | Critical | 9.8 | 100% | KEV + Ransom | - |
| CVE-2019-11043 | High | 8.7 | 100% | KEV + Ransom | Fix |
Common questions
How do I fix CVE-2023-40547?
Published advisories record a fix for 41 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2023-40547 being actively exploited?
Not that we know of. CVE-2023-40547 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 5.4% is the estimated probability that it will be exploited in the next 30 days. That is higher than 92% of all scored CVEs.
How severe is CVE-2023-40547?
CVE-2023-40547 has a CVSS v3 base score of 8.3, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2023-40547 affect?
Published advisories record a fix for shim (Debian), Windows 10 (Windows), Windows 10 Version 1607 (Windows), Windows 10 Version 1809 (Windows), and 37 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-26.