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CVE-2021-33781: Azure AD Security Feature Bypass Vulnerability

• Severity: medium (CVSS 5.5 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-07-14 · updated 2026-08-10

Description

Azure AD Security Feature Bypass Vulnerability

Affected products

• Microsoft Windows 10 Version 1607: 20h2, 21h1, 1809, 1909, 2004
• Microsoft Windows Server 2016: 20h2, 2004
• Microsoft Windows Server 2019: all versions
• Microsoft Windows 10 1607: from 10.0.14393.0 before 10.0.14393.4704 — fixed in 10.0.14393.4704
• Microsoft Windows 10: from 10.0.17763.0 before 10.0.17763.2061 — fixed in 10.0.17763.2061
• Microsoft Windows 10 1909: from 10.0.0 before 10.0.18363.1679 — fixed in 10.0.18363.1679
• Microsoft Windows 10 2004: from 10.0.0 before 10.0.19041.1110 — fixed in 10.0.19041.1110
• Microsoft Windows 10 20H2: from 10.0.0 before 10.0.19042.1110 — fixed in 10.0.19042.1110
• Microsoft Windows 10 21H1: from 10.0.0 before 10.0.19043.1110 — fixed in 10.0.19043.1110
• Microsoft Windows 11 21H2: from 10.0.22000.0 before 10.0.22000.258 — fixed in 10.0.22000.258
• Microsoft Windows Server 2016: from 10.0.14393.0 before 10.0.14393.4704 — fixed in 10.0.14393.4704
• Microsoft Windows Server 2019: from 10.0.17763.0 before 10.0.17763.2061 — fixed in 10.0.17763.2061
• Microsoft Windows Server version 2004: from 10.0.0 before 10.0.19041.1110 — fixed in 10.0.19041.1110
• Microsoft Windows Server version 20H2: from 10.0.0 before 10.0.19042.1110 — fixed in 10.0.19042.1110

How to fix

Upgrade to a fixed version: Microsoft Windows 10 1607 10.0.14393.4704; Microsoft Windows 10 10.0.17763.2061; Microsoft Windows 10 1909 10.0.18363.1679; Microsoft Windows 10 2004 10.0.19041.1110; Microsoft Windows 10 20H2 10.0.19042.1110; Microsoft Windows 10 21H1 10.0.19043.1110; Microsoft Windows 11 21H2 10.0.22000.258; Microsoft Windows Server 2016 10.0.14393.4704; Microsoft Windows Server 2019 10.0.17763.2061; Microsoft Windows Server version 2004 10.0.19041.1110; Microsoft Windows Server version 20H2 10.0.19042.1110. Check the vendor advisory for mitigations.

References

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-33781
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-33781

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