CVE-2026-21265

Boot trust degradation via expired Secure Boot certificates

Published Jan 13, 2026 · Updated Jan 13, 2026

Security feature bypass in Microsoft Windows Secure Boot allows local administrators to disrupt the boot trust chain via expiring certificates. The certificate update protection mechanism depends on UEFI firmware to replace the 2011 KEK and DB certificates, and defective firmware can reject or mishandle those trust-store writes. Secure Boot must be enabled and an affected 2011 certificate must remain; failed renewal blocks later Boot Manager, DB, and DBX protections while normal startup continues.

CVSS severity6.4
Medium
EPSS probability1.07%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Security feature bypass in Microsoft Windows Secure Boot allows local administrators to disrupt the boot trust chain via expiring certificates. The certificate update protection mechanism depends on UEFI firmware to replace the 2011 KEK and DB certificates, and defective firmware can reject or mishandle those trust-store writes. Secure Boot must be enabled and an affected 2011 certificate must remain; failed renewal blocks later Boot Manager, DB, and DBX protections while normal startup continues.

The record

CVE
CVE-2026-21265
Published
Jan 13, 2026
Updated
Jan 13, 2026
Vendor
Microsoft
Product
Windows Server 2019
Classifications
CWE-1329
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Jan 13, 2026CVE publishedPublication date reported by the CVE source.
  2. Jan 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.0.17763.0 <10.0.17763.8276

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

Microsoft · Windows Server 2019version=10.0.17763.0 <10.0.17763.8276
Microsoft · Windows Server 2025 (Server Core installation)version=10.0.26100.0 <10.0.26100.32230
Microsoft · Windows 11, version 25H2version=10.0.26200.0 <10.0.26200.7623
Microsoft · Windows Server 2016 (Server Core installation)version=10.0.14393.0 <10.0.14393.8783
Microsoft · Windows 11, version 24H2version=10.0.26100.0 <10.0.26100.7623
Microsoft · Windows Server 2012 (Server Core installation)version=6.2.9200.0 <6.2.9200.25868
Microsoft · Windows Server 2012version=6.2.9200.0 <6.2.9200.25868
Microsoft · Windows 10 Version 21H2version=10.0.19044.0 <10.0.19044.6809
Microsoft · Windows Server 2022, 23H2 Edition (Server Core installation)version=10.0.25398.0 <10.0.25398.2092
Microsoft · Windows Server 2016version=10.0.14393.0 <10.0.14393.8783
Microsoft · Windows 11 Version 22H3version=10.0.22631.0 <10.0.22631.6491
Microsoft · Windows 10 Version 22H2version=10.0.19045.0 <10.0.19045.6809
Microsoft · Windows Server 2012 R2 (Server Core installation)version=6.3.9600.0 <6.3.9600.22968
Microsoft · Windows Server 2019 (Server Core installation)version=10.0.17763.0 <10.0.17763.8276
Microsoft · Windows 11 Version 23H2version=10.0.22631.0 <10.0.22631.6491
Microsoft · Windows 10 Version 1607version=10.0.14393.0 <10.0.14393.8783
Microsoft · Windows Server 2022version=10.0.20348.0 <10.0.20348.4648
Microsoft · Windows Server 2025version=10.0.26100.0 <10.0.26100.32230
Microsoft · Windows 10 Version 1809version=10.0.17763.0 <10.0.17763.8276
Microsoft · Windows Server 2012 R2version=6.3.9600.0 <6.3.9600.22968

Published CVSS scores

6.4Microsoft CorporationCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-1329Reliance on Component That is Not Updateable

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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