Microsoft HTTP Protocol Stack Remote Code Execution Vulnerability

CRITICAL 9.8EXPLOITED (CISA KEV)CVE-2021-31166 · Published 11/05/2021 · updated 17/06/2026

Microsoft HTTP Protocol Stack Remote Code Execution Vulnerability. Actively exploited: CISA added this vulnerability to its Known Exploited Vulnerabilities catalog on 06/04/2022. Patch affected systems as an emergency.

In short

CVE-2021-31166 is a CRITICAL (CVSS 9.8) vulnerability.
Exploited in the wild: CISA added it to the KEV catalog on 06/04/2022.
Chance of exploitation in the next 30 days (EPSS): 99.9%, higher than 100.0% of all vulnerabilities.
No patched version is listed yet: follow the vendor's advisory in References.

Package	Affected versions	Patched versions
HTTP Protocol Stack Microsoft	Versions not published yet (product named by CISA KEV)

Description

HTTP Protocol Stack Remote Code Execution Vulnerability

References

packetstormsecurity.com/files/162722/Microsoft-HTTP-Protocol-Stack-Remote-Code-Execution.html · Third Party Advisory
portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31166 · Patch
cisa.gov/known-exploited-vulnerabilities-catalog · US Government Resource
CISA KEV · CVE-2021-31166

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