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CVE-2021-31166

CRITICAL9.8
CISA KEV

Published 2021-05-11 · Updated 2026-06-17 · Source secure@microsoft.com

Summary

CVE-2021-31166 is a critical-severity (CVSS 9.8) vulnerability in Microsoft HTTP Protocol Stack. CISA added it to the Known Exploited Vulnerabilities catalog on April 6, 2022, which means exploitation in the wild has been confirmed; US federal agencies had to remediate it by April 27, 2022. CISA does not currently list it as used in ransomware campaigns. Microsoft has 390 vulnerabilities in the KEV catalog, 117 of them linked to ransomware.

All 390 known-exploited Microsoft vulnerabilities →

Description

HTTP Protocol Stack Remote Code Execution Vulnerability

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE-416CWE-416

CISA Known-Exploited Vulnerability

Product: Microsoft — HTTP Protocol Stack

Name: Microsoft HTTP Protocol Stack Remote Code Execution Vulnerability

Date added: 2022-04-06 · Due: 2022-04-27

Required action: Apply updates per vendor instructions.

View on NVD