CVE-2026-21510: Windows Shell Security Feature Bypass Vulnerability | Rafael Pfister

Analysis on rafaelpfister.ch

Article · October 14, 2026 CVE-2026-96951: Windows Shell Mark of the Web Bypass Is Being Exploited—Install the October Update On October 13, 2026, Microsoft fixed an already exploited Windows Shell vulnerability (CVE-2026-96951, CVSS 8.8). Crafted files delivered by email or chat can bypass Mark of the Web protection. CISA lists the vulnerability in its KEV catalog; only the cumulative October update resolves it.

Vendor description

Protection mechanism failure in Windows Shell allows an unauthorized attacker to bypass a security feature over a network.

Reference data

Vendor

Microsoft

Affected products

Windows 10 Version 1607
Windows 10 Version 1809
Windows 10 Version 21H2
Windows 10 Version 22H2
Windows 11 version 22H3
Windows 11 Version 23H2
Windows 11 Version 24H2
Windows 11 Version 25H2
Windows 11 version 26H1
Windows 11 Version 26H1
Windows Server 2012
Windows Server 2012 (Server Core installation)
Windows Server 2012 R2
Windows Server 2012 R2 (Server Core installation)
Windows Server 2016
Windows Server 2016 (Server Core installation)
Windows Server 2019
Windows Server 2019 (Server Core installation)
Windows Server 2022
Windows Server 2022, 23H2 Edition (Server Core installation)
Windows Server 2025
Windows Server 2025 (Server Core installation)

CVSS 3.1

8.8 (HIGH)

Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

Weakness type

CWE-693: Protection Mechanism Failure

Published

February 10, 2026

In KEV catalog since

February 10, 2026

US federal deadline

March 3, 2026

Official sources

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