CVE-2026-21265

Name: CVE-2026-21265
Creator: NVD / NIST
Published: 2026-01-13T18:16:25.053+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.4/10EPSS 0.97%

Last modified Jun 17, 2026

CVE-2026-21265 is a medium-severity vulnerability rated 6.4/10 on the CVSS scale. 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. EPSS estimates a 0.97% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1

6.4/10

CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

0.97%

57.2th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-1329

Affected Software

Vendor	Product	Versions
Microsoft	Windows 10 1607	< 10.0.14393.8783
Microsoft	Windows 10 1809	< 10.0.17763.8276
Microsoft	Windows 10 21h2	< 10.0.19044.6809
Microsoft	Windows 10 22h2	< 10.0.19045.6809
Microsoft	Windows 11 23h2	< 10.0.22631.6491
Microsoft	Windows 11 24h2	< 10.0.26100.7623
Microsoft	Windows 11 25h2	< 10.0.26200.7623
Microsoft	Windows Server 2012	All versions
Microsoft	Windows Server 2012	r2
Microsoft	Windows Server 2016	< 10.0.14393.8783
Microsoft	Windows Server 2019	< 10.0.17763.8276
Microsoft	Windows Server 2022	< 10.0.20348.4648
Microsoft	Windows Server 2022 23h2	< 10.0.25398.2092
Microsoft	Windows Server 2025	< 10.0.26100.32230

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21265Vendor Advisory

Timeline

Published: Jan 13, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-21265?

How severe is CVE-2026-21265?

CVE-2026-21265 has a CVSS score of 6.4/10 (MEDIUM severity). The EPSS model estimates a 0.97% probability of exploitation in the next 30 days.

How do I fix CVE-2026-21265?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-21265?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST