Medium [CVE-2026-21265] Secure Boot Certificate Expiration Security Feature Bypass Vulnerability
This medium-severity Microsoft Server advisory covers CVE-2026-21265 affecting Windows Server 2012 (Server Core installation), Windows Server 2012 R2 (Server Core installation), Windows Server 2016 (Server Core installation).
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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 Signs updates to the DB and DBX
06/24/2026
DB Signs 3rd party boot loaders, Option ROMs, etc.
Microsoft Windows Production PCA 2011 Signs the Windows Boot Manager
For more information see this CVE and Windows Secure Boot certificate expiration and CA updates.
Affected products named by the advisory: Windows Server 2012; Windows Server 2012 (Server Core installation); Windows Server 2012 R2; Windows Server 2012 R2 (Server Core installation); and 8 more.
- Windows 10 Version 1607 10.0.14393.0 before 10.0.14393.8783
- Windows 10 Version 1809 10.0.17763.0 before 10.0.17763.8276
- Windows 10 Version 21H2 10.0.19044.0 before 10.0.19044.6809
- Windows 10 Version 22H2 10.0.19045.0 before 10.0.19045.6809
- Windows 11 version 23H2 10.0.22631.0 before 10.0.22631.6491
- Windows 11 Version 23H2 10.0.22631.0 before 10.0.22631.6491
- Windows 11 Version 24H2 10.0.26100.0 before 10.0.26100.7623
- Windows 11 Version 25H2 10.0.26200.0 before 10.0.26200.7623
- Windows Server 2012 6.2.9200.0 before 6.2.9200.25868
- Windows Server 2012 (Server Core installation) 6.2.9200.0 before 6.2.9200.25868
- Windows Server 2012 R2 6.3.9600.0 before 6.3.9600.22968
- Windows Server 2012 R2 (Server Core installation) 6.3.9600.0 before 6.3.9600.22968
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
- 10.0.14393.8783
- 10.0.17763.8276
- 10.0.19044.6809
- 10.0.19045.6809
- 10.0.22631.6491
- 10.0.26100.7623
- 10.0.26200.7623
- 6.2.9200.25868
- 6.3.9600.22968
- 10.0.20348.4648
- 10.0.25398.2092
- 10.0.26100.32230
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
Mitigation checklist
- 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.
Official advisory · high-confidence parse· fetched 2 months ago·verify at source
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