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CVE-2021-42286: Windows Core Shell SI Host Extension Framework for Composable Shell Elevation of Privilege Vulnerability

• Severity: medium (CVSS 4.6 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-11-10 · updated 2026-08-19
• Weakness: CWE-269

Description

Windows Core Shell SI Host Extension Framework for Composable Shell Elevation of Privilege Vulnerability

Affected products

• Microsoft Windows 10 Version 1607: 20h2, 21h1, 2004
• Microsoft Windows Server: 20h2
• Microsoft Windows Server 2016: 2004
• Microsoft Windows 10 2004: from 10.0.0 before 10.0.19041.1348 — fixed in 10.0.19041.1348
• Microsoft Windows 10 20H2: from 10.0.0 before 10.0.19042.1348 — fixed in 10.0.19042.1348
• Microsoft Windows 10 21H1: from 10.0.0 before 10.0.19043.1348 — fixed in 10.0.19043.1348
• Microsoft Windows Server version 2004: from 10.0.0 before 10.0.19041.1348 — fixed in 10.0.19041.1348
• Microsoft Windows Server version 20H2: from 10.0.0 before 10.0.19041.1348 — fixed in 10.0.19041.1348

How to fix

Upgrade to a fixed version: Microsoft Windows 10 2004 10.0.19041.1348; Microsoft Windows 10 20H2 10.0.19042.1348; Microsoft Windows 10 21H1 10.0.19043.1348; Microsoft Windows Server version 2004 10.0.19041.1348; Microsoft Windows Server version 20H2 10.0.19041.1348. Check the vendor advisory for mitigations.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-42286
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42286

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