Reference page — cumulative record through Sunday, October 4, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2021-31166

CVE-2021-31166CRITICAL

Microsoft Windows 10 Version 2004 — HTTP Protocol Stack Remote Code Execution Vulnerability

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS    %ile   KEV
   N   L   N   N  U  H  H  H    9.8   .9987   100.0   YES

AFFECTED
  Product                      Versions  Fixed
  Windows 10 Version 2004      10.0.0 –  —
  Windows Server version 2004  10.0.0 –  —
  Windows 10 Version 20H2      10.0.0 –  —
  Windows Server version 20H2  10.0.0 –  —

TIMELINE
  Apr 14  Reserved by microsoft
  May 11  Published (CNA: microsoft)
  Apr 6   Added to CISA KEV, remediation due 2022-04-27

CWE-416 · CNA: microsoft · CVSS v3.1 · 3 references · KEV due April 27, 2022

Description

HTTP Protocol Stack Remote Code Execution Vulnerability

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
April 14, 2021	Reserved	Reserved by microsoft
May 11, 2021	Published	Published (CNA: microsoft)
April 6, 2022	KEV ADDED	Added to CISA KEV, remediation due 2022-04-27

Affected

Affected products and packages — 4 rows
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
Microsoft	Windows 10 Version 2004	—	10.0.0	—
Microsoft	Windows Server version 2004	—	10.0.0	—
Microsoft	Windows 10 Version 20H2	—	10.0.0	—
Microsoft	Windows Server version 20H2	—	10.0.0	—

Weaknesses

CWE-416

References (3)

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

Authoritative record: CVE-2021-31166 at cve.org

Vendors: microsoft

Weaknesses: CWE-416

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2021-31166 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Sunday, October 4, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.