CVE-2026-21265
MEDIUMDescription
Windows Secure Boot stores Microsoft certificates in the UEFI KEK and DB. These original certificates are approaching expiration, and devices containing affected certificate versions must update them to maintain Secure Boot functionality and avoid compromising security by losing security fixes related to Windows boot manager or Secure Boot. The operating system’s certificate update protection mechanism relies on firmware components that might contain defects, which can cause certificate trust updates to fail or behave unpredictably. This leads to potential disruption of the Secure Boot trust chain and requires careful validation and deployment to restore intended security guarantees. Certificate Authority (CA) Location Purpose Expiration Date Microsoft Corporation KEK CA 2011 KEK Signs updates to the DB and DBX 06/24/2026 Microsoft Corporation UEFI CA 2011 DB Signs 3rd party boot loaders, Option ROMs, etc. 06/27/2026 Microsoft Windows Production PCA 2011 DB Signs the Windows Boot Manager 10/19/2026 For more information see this CVE and Windows Secure Boot certificate expiration and CA updates.
How to fix
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:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Exploit Intelligence
Moderate risk: more likely to be exploited than 58% of all known CVEs.
References
Related Vulnerabilities
Other CWE-1329 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2026-41097 | High | 6.7 | 1.4% | - | Fix |
| CVE-2026-48573 | High | 7.9 | 1.0% | - | Fix |
| CVE-2026-48576 | High | 7.9 | 1.0% | - | Fix |
| CVE-2022-34381 | Critical | 9.1 | 1.0% | - | Fix |
| CVE-2021-38398 | Medium | 6.5 | 0.4% | - | - |
Common questions
How do I fix CVE-2026-21265?
Published advisories record a fix for 20 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-2026-21265 being actively exploited?
Not that we know of. CVE-2026-21265 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.97% is the estimated probability that it will be exploited in the next 30 days. That is higher than 58% of all scored CVEs.
How severe is CVE-2026-21265?
CVE-2026-21265 has a CVSS v3 base score of 6.4, rated medium. 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-2026-21265 affect?
Published advisories record a fix for Windows 10 Version 1607 (Windows), Windows 10 Version 1809 (Windows), Windows 10 Version 21H2 (Windows), Windows 10 Version 22H2 (Windows), and 16 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
Embed a live status badge for CVE-2026-21265
Markdown
[](https://tridentstack.com/cve/CVE-2026-21265)HTML
<a href="https://tridentstack.com/cve/CVE-2026-21265"><img src="https://tridentstack.com/cve/badge/CVE-2026-21265.svg" alt="CVE-2026-21265"></a>Find and fix vulnerabilities across your fleet
TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.
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 2026-07-30.