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CVE-2021-31977: Windows Hyper-V Denial of Service Vulnerability

• Severity: medium (CVSS 5.0 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 3.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-06-08 · updated 2026-06-17
• Weakness: CWE-119

Description

Windows Hyper-V Denial of Service Vulnerability

Affected products

• Microsoft Windows 10 Version 1607: 20h2, 21h1, 1607, 1809, 1909, 2004
• Microsoft Windows Server 2016: 20h2, 1909, 2004
• Microsoft Windows Server 2019: all versions
• Microsoft Windows 10 Version 1507: from 10.0.0 before 10.0.10240.18967 — fixed in 10.0.10240.18967
• Microsoft Windows 10 1607: from 10.0.0 before 10.0.14393.4467 — fixed in 10.0.14393.4467
• Microsoft Windows 10: from 10.0.0 before 10.0.17763.1999 — fixed in 10.0.17763.1999
• Microsoft Windows 10 1909: from 10.0.0 before 10.0.18363.1621 — fixed in 10.0.18363.1621
• Microsoft Windows 10 2004: from 10.0.0 before 10.0.19041.1052 — fixed in 10.0.19041.1052
• Microsoft Windows 10 21H1: from 10.0.0 before 10.0.19043.1052 — fixed in 10.0.19043.1052
• Microsoft Windows Server 2016: from 10.0.0 before 10.0.14393.4467 — fixed in 10.0.14393.4467
• Microsoft Windows Server 2019: from 10.0.0 before 10.0.17763.1999 — fixed in 10.0.17763.1999
• Microsoft Windows Server version 2004: from 10.0.0 before 10.0.19041.1052 — fixed in 10.0.19041.1052
• Microsoft Windows Server version 20H2: from 10.0.0 before 10.0.19042.1052 — fixed in 10.0.19042.1052

How to fix

Upgrade to a fixed version: Microsoft Windows 10 Version 1507 10.0.10240.18967; Microsoft Windows 10 1607 10.0.14393.4467; Microsoft Windows 10 10.0.17763.1999; Microsoft Windows 10 1909 10.0.18363.1621; Microsoft Windows 10 2004 10.0.19041.1052; Microsoft Windows 10 21H1 10.0.19043.1052; Microsoft Windows Server 2016 10.0.14393.4467; Microsoft Windows Server 2019 10.0.17763.1999; Microsoft Windows Server version 2004 10.0.19041.1052; Microsoft Windows Server version 20H2 10.0.19042.1052. Check the vendor advisory for mitigations.

References

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31977
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31977

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