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CVE-2021-31166: HTTP Protocol Stack Remote Code Execution Vulnerability

• Severity: high (CVSS 7.5 v2.0)
• Exploited in the wild: yes — in CISA KEV since 2022-04-06
• EPSS: 99.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-05-11 · updated 2026-06-17
• Weakness: CWE-416

Description

HTTP Protocol Stack Remote Code Execution Vulnerability

Affected products

• Microsoft Windows 10 2004: before 10.0.19041.982 — fixed in 10.0.19041.982
• Microsoft Windows 10 20H2: before 10.0.19042.982 — fixed in 10.0.19042.982
• Microsoft Windows Server 2004: before 10.0.19041.982 — fixed in 10.0.19041.982
• Microsoft Windows Server 20H2: before 10.0.19042.982 — fixed in 10.0.19042.982
• Microsoft Windows 10 2004: from 10.0.0 before 10.0.19041.982 — fixed in 10.0.19041.982
• Microsoft Windows 10 20H2: from 10.0.0 before 10.0.19042.982 — fixed in 10.0.19042.982
• Microsoft Windows Server version 2004: from 10.0.0 before 10.0.19041.982 — fixed in 10.0.19041.982
• Microsoft Windows Server version 20H2: from 10.0.0 before 10.0.19042.982 — fixed in 10.0.19042.982

How to fix

Upgrade to a fixed version: Microsoft Windows 10 2004 10.0.19041.982; Microsoft Windows 10 20H2 10.0.19042.982; Microsoft Windows Server 2004 10.0.19041.982; Microsoft Windows Server 20H2 10.0.19042.982; Microsoft Windows 10 2004 10.0.19041.982; Microsoft Windows 10 20H2 10.0.19042.982; Microsoft Windows Server version 2004 10.0.19041.982; Microsoft Windows Server version 20H2 10.0.19042.982. Check the vendor advisory for mitigations.

References

• http://packetstormsecurity.com/files/162722/Microsoft-HTTP-Protocol-Stack-Remote-Code-Execution.html
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31166
• http://packetstormsecurity.com/files/162722/Microsoft-HTTP-Protocol-Stack-Remote-Code-Execution.html
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31166
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31166

Get alerted when CVE-2021-31166 or the next vulnerability affects your stack