ゼットスケーラーのセキュリティアドバイザリ
セキュリティ アドバイザリー -
February 10, 2026
Zscaler protects against 9 new vulnerabilities for Windows
Zscaler, working with Microsoft through their MAPP program, has proactively deployed protection for the following 9 vulnerabilities included in the February 2026 Microsoft security bulletins. Zscaler will continue to monitor exploits associated with all vulnerabilities in the February release and deploy additional protections, as necessary.
CVE-2026-21231 – Windows Kernel Elevation of Privilege Vulnerability
Severity: Important
Subscriptions Required
- Advanced Cloud Sandbox
- Advanced Threat Protection
Affected Software
- Windows 11 version 26H1 for x64-based Systems
- Windows 11 Version 26H1 for ARM64-based Systems
- Windows Server 2012 R2 (Server Core installation)
- Windows Server 2012 R2
- Windows Server 2012 (Server Core installation)
- Windows Server 2012
- Windows Server 2016 (Server Core installation)
- Windows Server 2016
- Windows 10 Version 1607 for x64-based Systems
- Windows 10 Version 1607 for 32-bit Systems
- Windows Server 2025
- Windows 11 Version 24H2 for x64-based Systems
- Windows 11 Version 24H2 for ARM64-based Systems
- Windows Server 2022, 23H2 Edition (Server Core installation)
- Windows 11 Version 23H2 for x64-based Systems
- Windows 11 Version 23H2 for ARM64-based Systems
- Windows 11 Version 25H2 for x64-based Systems
- Windows 11 Version 25H2 for ARM64-based Systems
- Windows Server 2025 (Server Core installation)
- Windows 10 Version 22H2 for 32-bit Systems
- Windows 10 Version 22H2 for ARM64-based Systems
- Windows 10 Version 22H2 for x64-based Systems
- Windows 10 Version 21H2 for x64-based Systems
- Windows 10 Version 21H2 for ARM64-based Systems
- Windows 10 Version 21H2 for 32-bit Systems
- Windows Server 2022 (Server Core installation)
- Windows Server 2022
- Windows Server 2019 (Server Core installation)
- Windows Server 2019
- Windows 10 Version 1809 for x64-based Systems
- Windows 10 Version 1809 for 32-bit Systems
CVE-2026-21238 – Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability
Severity: Important
Subscriptions Required
- Advanced Threat Protection
- Advanced Cloud Sandbox
Affected Software
- Windows Server 2012 R2 (Server Core installation)
- Windows Server 2012 R2
- Windows Server 2012 (Server Core installation)
- Windows Server 2012
- Windows Server 2016 (Server Core installation)
- Windows Server 2016
- Windows 10 Version 1607 for x64-based Systems
- Windows 10 Version 1607 for 32-bit Systems
- Windows Server 2025
- Windows 11 Version 24H2 for x64-based Systems
- Windows 11 Version 24H2 for ARM64-based Systems
- Windows Server 2022, 23H2 Edition (Server Core installation)
- Windows 11 Version 23H2 for x64-based Systems
- Windows 11 Version 23H2 for ARM64-based Systems
- Windows 11 Version 25H2 for x64-based Systems
- Windows 11 Version 25H2 for ARM64-based Systems
- Windows Server 2025 (Server Core installation)
- Windows 10 Version 22H2 for 32-bit Systems
- Windows 10 Version 22H2 for ARM64-based Systems
- Windows 10 Version 22H2 for x64-based Systems
- Windows 10 Version 21H2 for x64-based Systems
- Windows 10 Version 21H2 for ARM64-based Systems
- Windows 10 Version 21H2 for 32-bit Systems
- Windows Server 2022 (Server Core installation)
- Windows Server 2022
- Windows Server 2019 (Server Core installation)
- Windows Server 2019
- Windows 10 Version 1809 for x64-based Systems
- Windows 10 Version 1809 for 32-bit Systems
- Windows 11 version 26H1 for x64-based Systems
- Windows 11 Version 26H1 for ARM64-based Systems
CVE-2026-21241 – Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability
Severity: Important
Subscriptions Required
- Advanced Cloud Sandbox
- Advanced Threat Protection
Affected Software
- Windows Server 2025
- Windows 11 Version 24H2 for x64-based Systems
- Windows 11 Version 24H2 for ARM64-based Systems
- Windows Server 2022, 23H2 Edition (Server Core installation)
- Windows 11 Version 23H2 for x64-based Systems
- Windows 11 Version 23H2 for ARM64-based Systems
- Windows 11 Version 25H2 for x64-based Systems
- Windows 11 Version 25H2 for ARM64-based Systems
- Windows Server 2025 (Server Core installation)
- Windows Server 2022 (Server Core installation)
- Windows Server 2022
- Windows 11 version 26H1 for x64-based Systems
- Windows 11 Version 26H1 for ARM64-based Systems
CVE-2026-21253 – Mailslot File System Elevation of Privilege Vulnerability
Severity: Important
Subscriptions Required
- Advanced Cloud Sandbox
- Advanced Threat Protection
Affected Software
- Windows Server 2016 (Server Core installation)
- Windows 10 Version 1607 for 32-bit Systems
- Windows 10 Version 1607 for x64-based Systems
- Windows Server 2016
- Windows Server 2025
- Windows 11 Version 24H2 for x64-based Systems
- Windows 11 Version 24H2 for ARM64-based Systems
- Windows Server 2022, 23H2 Edition (Server Core installation)
- Windows 11 Version 23H2 for x64-based Systems
- Windows 11 Version 23H2 for ARM64-based Systems
- Windows 11 Version 25H2 for x64-based Systems
- Windows 11 Version 25H2 for ARM64-based Systems
- Windows Server 2025 (Server Core installation)
- Windows 10 Version 22H2 for 32-bit Systems
- Windows 10 Version 22H2 for ARM64-based Systems
- Windows 10 Version 22H2 for x64-based Systems
- Windows Server 2019 (Server Core installation)
- Windows Server 2019
- Windows 10 Version 1809 for 32-bit Systems
- Windows Server 2022 (Server Core installation)
- Windows Server 2012 R2 (Server Core installation)
- Windows Server 2012
- Windows Server 2012 R2
- Windows Server 2012 (Server Core installation)
- Windows 10 Version 21H2 for 32-bit Systems
- Windows 10 Version 1809 for x64-based Systems
- Windows 10 Version 21H2 for x64-based Systems
- Windows 10 Version 21H2 for ARM64-based Systems
- Windows Server 2022
- Windows 11 version 26H1 for x64-based Systems
- Windows 11 Version 26H1 for ARM64-based Systems
CVE-2026-21510 – Windows Shell Security Feature Bypass Vulnerability
Severity: Important
Subscriptions Required
- Advanced Threat Protection
Affected Software
- Windows 11 version 26H1 for x64-based Systems
- Windows 11 Version 26H1 for ARM64-based Systems
- Windows Server 2012 R2 (Server Core installation)
- Windows Server 2012 R2
- Windows Server 2012 (Server Core installation)
- Windows Server 2012
- Windows Server 2016 (Server Core installation)
- Windows Server 2016
- Windows 10 Version 1607 for x64-based Systems
- Windows 10 Version 1607 for 32-bit Systems
- Windows Server 2025
- Windows 11 Version 24H2 for x64-based Systems
- Windows 11 Version 24H2 for ARM64-based Systems
- Windows Server 2022, 23H2 Edition (Server Core installation)
- Windows 11 Version 23H2 for x64-based Systems
- Windows 11 Version 23H2 for ARM64-based Systems
- Windows 11 Version 25H2 for x64-based Systems
- Windows 11 Version 25H2 for ARM64-based Systems
- Windows Server 2025 (Server Core installation)
- Windows 10 Version 22H2 for 32-bit Systems
- Windows 10 Version 22H2 for ARM64-based Systems
- Windows 10 Version 22H2 for x64-based Systems
- Windows 10 Version 21H2 for x64-based Systems
- Windows 10 Version 21H2 for ARM64-based Systems
- Windows 10 Version 21H2 for 32-bit Systems
- Windows Server 2022 (Server Core installation)
- Windows Server 2022
- Windows Server 2019 (Server Core installation)
- Windows Server 2019
- Windows 10 Version 1809 for x64-based Systems
- Windows 10 Version 1809 for 32-bit Systems
CVE-2026-21511 – Microsoft Outlook Spoofing Vulnerability
Severity: Important
Subscriptions Required
- Advanced Cloud Sandbox
- Advanced Threat Protection
Affected Software
- Microsoft Office LTSC for Mac 2021
- Microsoft 365 Apps for Enterprise for 64-bit Systems
- Microsoft 365 Apps for Enterprise for 32-bit Systems
- Microsoft Office 2019 for 64-bit editions
- Microsoft Office 2019 for 32-bit editions
- Microsoft SharePoint Server 2019
- Microsoft SharePoint Enterprise Server 2016
- Microsoft Word 2016 (64-bit edition)
- Microsoft Word 2016 (32-bit edition)
- Microsoft Office LTSC for Mac 2024
- Microsoft Office LTSC 2024 for 64-bit editions
- Microsoft Office LTSC 2024 for 32-bit editions
- Microsoft SharePoint Server Subscription Edition
- Microsoft Office LTSC 2021 for 32-bit editions
- Microsoft Office LTSC 2021 for 64-bit editions
CVE-2026-21514 – Microsoft Word Security Feature Bypass Vulnerability
Severity: Important
Subscriptions Required
- Advanced Cloud Sandbox
- Advanced Threat Protection
Affected Software
- Microsoft Office LTSC for Mac 2024
- Microsoft Office LTSC 2024 for 64-bit editions
- Microsoft Office LTSC 2024 for 32-bit editions
- Microsoft Office LTSC 2021 for 32-bit editions
- Microsoft Office LTSC 2021 for 64-bit editions
- Microsoft Office LTSC for Mac 2021
- Microsoft 365 Apps for Enterprise for 64-bit Systems
- Microsoft 365 Apps for Enterprise for 32-bit Systems
CVE-2026-21519 – Desktop Window Manager Elevation of Privilege Vulnerability
Severity: Important
Subscriptions Required
- Advanced Cloud Sandbox
- Advanced Threat Protection
Affected Software
- Windows 11 version 26H1 for x64-based Systems
- Windows 11 Version 26H1 for ARM64-based Systems
- Windows Server 2016 (Server Core installation)
- Windows Server 2016
- Windows 10 Version 1607 for x64-based Systems
- Windows 10 Version 1607 for 32-bit Systems
- Windows Server 2025
- Windows 11 Version 24H2 for x64-based Systems
- Windows 11 Version 24H2 for ARM64-based Systems
- Windows Server 2022, 23H2 Edition (Server Core installation)
- Windows 11 Version 23H2 for x64-based Systems
- Windows 11 Version 23H2 for ARM64-based Systems
- Windows 11 Version 25H2 for x64-based Systems
- Windows 11 Version 25H2 for ARM64-based Systems
- Windows Server 2025 (Server Core installation)
- Windows 10 Version 22H2 for 32-bit Systems
- Windows 10 Version 22H2 for ARM64-based Systems
- Windows 10 Version 22H2 for x64-based Systems
- Windows 10 Version 21H2 for x64-based Systems
- Windows 10 Version 21H2 for ARM64-based Systems
- Windows 10 Version 21H2 for 32-bit Systems
- Windows Server 2022 (Server Core installation)
- Windows Server 2022
- Windows Server 2019 (Server Core installation)
- Windows Server 2019
- Windows 10 Version 1809 for x64-based Systems
- Windows 10 Version 1809 for 32-bit Systems
CVE-2026-21525 – Windows Remote Access Connection Manager Denial of Service Vulnerability
Severity: Moderate
Subscriptions Required
- Advanced Threat Protection
- Advanced Cloud Sandbox
Affected Software
- Windows 11 version 26H1 for x64-based Systems
- Windows 11 Version 26H1 for ARM64-based Systems
- Windows Server 2012 R2 (Server Core installation)
- Windows Server 2012 R2
- Windows Server 2012 (Server Core installation)
- Windows Server 2012
- Windows Server 2016 (Server Core installation)
- Windows Server 2016
- Windows 10 Version 1607 for x64-based Systems
- Windows 10 Version 1607 for 32-bit Systems
- Windows Server 2025
- Windows 11 Version 24H2 for x64-based Systems
- Windows 11 Version 24H2 for ARM64-based Systems
- Windows Server 2022, 23H2 Edition (Server Core installation)
- Windows 11 Version 23H2 for x64-based Systems
- Windows 11 Version 23H2 for ARM64-based Systems
- Windows 11 Version 25H2 for x64-based Systems
- Windows 11 Version 25H2 for ARM64-based Systems
- Windows Server 2025 (Server Core installation)
- Windows 10 Version 22H2 for 32-bit Systems
- Windows 10 Version 22H2 for ARM64-based Systems
- Windows 10 Version 22H2 for x64-based Systems
- Windows 10 Version 21H2 for x64-based Systems
- Windows 10 Version 21H2 for ARM64-based Systems
- Windows 10 Version 21H2 for 32-bit Systems
- Windows Server 2022 (Server Core installation)
- Windows Server 2022
- Windows Server 2019 (Server Core installation)
- Windows Server 2019
- Windows 10 Version 1809 for x64-based Systems
- Windows 10 Version 1809 for 32-bit Systems