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Fencer Vulns
medium 6.4

CVE-2026-21265 json

Secure Boot Certificate Expiration Security Feature Bypass Vulnerability

published 2026-01-13 9 mo ago modified 2026-07-30 3 mo ago also EUVD-2026-2100

cvss
6.4
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.1%
EPSS 1.1% chance of exploitation in 30 days, percentile 65%
public exploits
0
none known

Summary

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.

Patch / fix

  • Microsoft Windows 10 Version 1607 10.0.14393.8783
  • Microsoft Windows 10 Version 1809 10.0.17763.8276
  • Microsoft Windows 10 Version 21H2 10.0.19044.6809
  • Microsoft Windows 10 Version 22H2 10.0.19045.6809
  • Microsoft Windows 11 version 23H2 10.0.22631.6491
  • Microsoft Windows 11 Version 24H2 10.0.26100.7623
  • Microsoft Windows 11 Version 25H2 10.0.26200.7623
  • Microsoft Windows Server 2012 6.2.9200.25868
  • Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.25868
  • Microsoft Windows Server 2012 R2 6.3.9600.22968
  • Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.22968
  • Microsoft Windows Server 2016 10.0.14393.8783
  • Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.8783
  • Microsoft Windows Server 2019 10.0.17763.8276
  • Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.8276
  • Microsoft Windows Server 2022 10.0.20348.4648
  • Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.2092
  • Microsoft Windows Server 2025 10.0.26100.32230
  • Microsoft Windows Server 2025 (Server Core installation) 10.0.26100.32230

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
9 mo ago

Exploit prediction

1.10% chance of exploitation in the next 30 days, higher than 65% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.4 CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
CNA 3.1 6.4 CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Microsoft Windows 10 Version 1607
  • Microsoft Windows 10 Version 1809
  • Microsoft Windows 10 Version 21H2
  • Microsoft Windows 10 Version 22H2
  • Microsoft Windows 11 version 23H2
  • Microsoft Windows 11 Version 24H2
  • Microsoft Windows 11 Version 25H2
  • Microsoft Windows Server 2012
  • Microsoft Windows Server 2012 (Server Core installation)
  • Microsoft Windows Server 2012 R2
  • Microsoft Windows Server 2012 R2 (Server Core installation)
  • Microsoft Windows Server 2016
  • Microsoft Windows Server 2016 (Server Core installation)
  • Microsoft Windows Server 2019
  • Microsoft Windows Server 2019 (Server Core installation)
  • Microsoft Windows Server 2022
  • Microsoft Windows Server 2022, 23H2 Edition (Server Core installation)
  • Microsoft Windows Server 2025
  • Microsoft Windows Server 2025 (Server Core installation)

Classification

Weakness
  • CWE-1329 Reliance on Component That is Not Updateable

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.