How severe is CVE-2021-31166?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2021-31166 known to be exploited?

Yes. CVE-2021-31166 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-04-06), indicating it is being actively exploited. 76 public proof-of-concept repositories are indexed.

Vulnerability in Microsoft Windows 10 Version 2004

CVE-2021-31166

HTTP Protocol Stack Remote Code Execution Vulnerability

EPSS: 0.931 (99.8th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C.

Affected products

Microsoft Windows 10 Version 2004 — versions 10.0.0
Microsoft Windows 10 Version 20h2 — versions 10.0.0
Microsoft Windows Server Version 2004 — versions 10.0.0
Microsoft Windows Server Version 20h2 — versions 10.0.0

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2022-04-06. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2022-04-27.

Required action: Apply updates per vendor instructions.

Public proof-of-concept exploits

References

portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31166 (x_refsource_MISC)
packetstormsecurity.com/files/162722/Microsoft-HTTP-Protocol-Stack-Remote-Code-… (x_refsource_MISC)

Frequently asked questions

What is CVE-2021-31166?: CVE-2021-31166 is a critical-severity vulnerability in Microsoft Windows 10 Version 2004. CVSS score: 9.8/10. Published 2021-05-11.
How severe is CVE-2021-31166?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-31166 known to be exploited?: Yes. CVE-2021-31166 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-04-06), indicating it is being actively exploited. 76 public proof-of-concept repositories are indexed.