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Security Feature Bypass Vulnerability in Windows Secure Boot 

Indian – Computer Emergency Response Team (https://www.cert-in.org.in)

Severity Rating: HIGH

Software Affected

Windows 10 Version 1607 for 32-bit Systems, x64-based Systems

Windows 10 Version 1809 for 32-bit Systems, x64-based Systems

Windows 10 Version 21H2 for 32-bit Systems, x64-based Systems, ARM64-based Systems

Windows 10 Version 22H2 for 32-bit Systems, x64-based Systems, ARM64-based Systems

Windows 11 Version 23H2 for x64-based Systems, ARM64-based Systems

Windows 11 Version 24H2 for x64-based Systems, ARM64-based Systems

Windows 11 Version 25H2 for x64-based Systems, ARM64-based Systems

Windows Server 2012

Windows Server 2012 R2

Windows Server 2016

Windows Server 2019

Windows Server 2022

Windows Server 2025

Windows Server 2012 (Server Core installation)

Windows Server 2012 R2 (Server Core installation)

Windows Server 2016 (Server Core installation)

Windows Server 2019 (Server Core installation)

Windows Server 2022 (Server Core installation)

Windows Server 2022, 23H2 Edition (Server Core installation)

Windows Server 2025 (Server Core installation)

Microsoft certificates in the UEFI KEK and DB

Overview

A vulnerability has been reported in Windows Secure Boot which could allow an attacker to bypass security restrictions on the affected system.

Target Audience:

All end-user organizations and individuals using Windows systems with Secure Boot enabled.

Risk Assessment:

Risk of unauthorized system access.

Impact Assessment:

Potential for compromise of system boot integrity.

Description

Windows Secure Boot is a security feature that ensures a computer boots using only trusted, digitally signed firmware and operating system components, protecting against boot-level malware and rootkits.

This vulnerability exists in Windows Secure Boot due to improper handling of Secure Boot certificates in the UEFI firmware. An attacker with local administrative privileges could exploit this vulnerability to bypass Secure Boot protections.

Successful exploitation of the vulnerability could allow the attacker to load untrusted or malicious boot components during system startup resulting in compromising security of the affected system.

Note: These certificates are nearing expiration, and affected devices must update them to preserve Secure Boot functionality and prevent loss of critical security protections for the Windows Boot Manager and Secure Boot.

Solution

Apply appropriate security updates as mentioned in

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

Vendor Information

Microsoft

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

References

 

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

CVE Name

CVE-2026-21265

 

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Thanks and Regards,

CERT-In

Incident Response Help Desk

e-mail: incident@cert-in.org.in

Phone: +91-11-22902657

Toll Free Number: 1800-11-4949

Toll Free Fax : 1800-11-6969

Web: http://www.cert-in.org.in

PGP Fingerprint: A768 083E 4475 5725 B81A A379 2156 C0C0 B620 D0B4

PGP Key information:

https://www.cert-in.org.in/s2cMainServlet?pageid=CONTACTUS

Postal address:

Indian Computer Emergency Response Team (CERT-In)

Ministry of Electronics and Information Technology

Government of India

Electronics Niketan

6, C.G.O. Complex

New Delhi-110 003

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