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CVE-2021-31166

98
FAUCET Score

CVE-2021-31166 is a critical Remote Code Execution vulnerability affecting the HTTP Protocol Stack in various versions of Microsoft Windows 10 and Windows Server. With a CVSS score of 9.8, it presents a severe risk as it can be exploited remotely without authentication and has a high impact on confidentiality, integrity, and availability. This vulnerability is actively exploited in the wild, as indicated by its presence in the KEV catalog, and has garnered significant community attention and media coverage, including a Metasploit module for denial-of-service. Its wormable nature and high FAUCET Risk Score of 100/100 underscore the urgency for patching.

Impacted Technologies

VendorProductVersion(s)CPE
< 10.0.19041.982CPE matchmatch criteria
cpe:2.3:o:microsoft:windows_10_2004:*:*:*:*:*:*:*:*
< 10.0.19042.982CPE matchmatch criteria
cpe:2.3:o:microsoft:windows_10_20h2:*:*:*:*:*:*:*:*
< 10.0.19041.982CPE matchmatch criteria
cpe:2.3:o:microsoft:windows_server_2004:*:*:*:*:*:*:*:*
< 10.0.19042.982CPE matchmatch criteria
cpe:2.3:o:microsoft:windows_server_20h2:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.8CRITICAL

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
99.66%
Probability of exploitation in next 30 days
EPSS Percentile
99.9%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
Added to KEV · Apr 6, 2022
Metasploit: Windows IIS HTTP Protocol Stack DOS · May 11, 2021
This CVE's current EPSS score of 0.9966 is in the 100th percentile among its peer group of 36,897 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (8)

microsoftpatch availablevia nvd_reference
View patch
microsoftpatch availablevia msrc
Product: Windows 10 Version 2004 for 32-bit SystemsFixed in: 10.0.19041.982
View patch
microsoftpatch availablevia msrc
Product: Windows 10 Version 2004 for ARM64-based SystemsFixed in: 10.0.19041.982
View patch
microsoftpatch availablevia msrc
Product: Windows 10 Version 2004 for x64-based SystemsFixed in: 10.0.19041.982
View patch
microsoftpatch availablevia msrc
Product: Windows Server, version 2004 (Server Core installation)Fixed in: 10.0.19041.982
View patch
microsoftpatch availablevia msrc
Product: Windows 10 Version 20H2 for 32-bit SystemsFixed in: 10.0.19042.982
View patch
microsoftpatch availablevia msrc
Product: Windows 10 Version 20H2 for ARM64-based SystemsFixed in: 10.0.19042.982
View patch
microsoftpatch availablevia msrc
Product: Windows Server, version 20H2 (Server Core Installation)Fixed in: 10.0.19042.982
View patch

Vendor Advisories (1)

microsoft2021-May/CVE-2021-31166Critical

HTTP Protocol Stack Remote Code Execution Vulnerability

May 11, 2021

References

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