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CVE-2021-26431: Windows Recovery Environment Agent Elevation of Privilege Vulnerability

• Severity: medium (CVSS 4.6 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-08-12 · updated 2026-08-10

Description

Windows Recovery Environment Agent Elevation of Privilege Vulnerability

Affected products

• Microsoft Windows 10 Version 1607: 20h2, 21h1, 2004
• Microsoft Windows Server 2016: 20h2, 2004
• Microsoft Windows 10 2004: from 10.0.0 before 10.0.19041.1165 — fixed in 10.0.19041.1165
• Microsoft Windows 10 20H2: from 10.0.0 before 10.0.19042.1165 — fixed in 10.0.19042.1165
• Microsoft Windows 10 21H1: from 10.0.0 before 10.0.19043.1165 — fixed in 10.0.19043.1165
• Microsoft Windows Server version 2004: from 10.0.0 before 10.0.19041.1165 — fixed in 10.0.19041.1165
• Microsoft Windows Server version 20H2: from 10.0.0 before 10.0.19042.1165 — fixed in 10.0.19042.1165

How to fix

Upgrade to a fixed version: Microsoft Windows 10 2004 10.0.19041.1165; Microsoft Windows 10 20H2 10.0.19042.1165; Microsoft Windows 10 21H1 10.0.19043.1165; Microsoft Windows Server version 2004 10.0.19041.1165; Microsoft Windows Server version 20H2 10.0.19042.1165. Check the vendor advisory for mitigations.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-26431
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26431
• https://www.zerodayinitiative.com/advisories/ZDI-21-1053/

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