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Home - Vulnerability NotesPrint
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CERT-In Vulnerability Note CIVN-2026-0018
Security Feature Bypass Vulnerability in Windows Secure Boot

Original Issue Date:January 14, 2026

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

Disclaimer

The information provided herein is on "as is" basis, without warranty of any kind.

Contact Information

Email: info@cert-in.org.in
Phone: +91-11-22902657

Postal address

Indian Computer Emergency Response Team (CERT-In)
Ministry of Electronics and Information Technology
Government of India
Electronics Niketan
6, CGO Complex, Lodhi Road,
New Delhi - 110 003
India

 
Indian Computer Emergency Response Team - CERT-In, Ministry of Electronics and Information Technology, Government of India.
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