CVE-2026-21265: Microsoft Secure Boot Certificate Expiration Security Feature Bypass Vulnerability
This Microsoft advisory covers CVE-2026-21265 in Windows Server 2012 (Server Core installation), Windows Server 2012 R2 (Server Core installation) and Windows Server 2016 (Server Core installation).
- CVE-2026-21265
Key facts
- Vendor rating
- Medium, CVSS 6.4
- CISA KEV
- Not listed (catalogue checked )
- Affected
- 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 and 9 more below
- Fixed in
- 10.0.14393.8783, 10.0.17763.8276, 10.0.19044.6809 and 9 more below
- Source published
- Source revised
- Listed by VulniPulse
Compiled by VulniPulse from the linked sources. How records are collected and checked.
Affected products & platforms
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 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.
Text from the source record.
- 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 ·verify at source
How to fix CVE-2026-21265
Upgrade to a fixed release named by Microsoft:
- 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
Vendor guidance
- 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.
End-of-life dates for Windows Server
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