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CVE-2021-31166

HTTP Protocol Stack Remote Code Execution Vulnerability

9.8 CriticalIn KEVPublic exploit

HTTP Protocol Stack Remote Code Execution Vulnerability

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

99.9%Up 98.9 points since May 12, 2021
90%50%10%1%

What each source reports

CVE List Score used 9.8

HTTP Protocol Stack Remote Code Execution Vulnerability

HTTP Protocol Stack Remote Code Execution Vulnerability

Record
CVE-2021-31166
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Weakness
CWE-416
Updated
2026-11-02
EUVDEUVD-2021-18079 9.8

HTTP Protocol Stack Remote Code Execution Vulnerability

Record
EUVD-2021-18079
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Updated
2026-11-02
GitHub AdvisoriesGHSA-3mj9-c62w-jw5w 9.8

HTTP Protocol Stack Remote Code Execution Vulnerability

HTTP Protocol Stack Remote Code Execution Vulnerability

Record
GHSA-3mj9-c62w-jw5w
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-416
Updated
2026-11-02
CISA KEV No score

Microsoft HTTP Protocol Stack Remote Code Execution Vulnerability

Microsoft HTTP Protocol Stack contains a vulnerability in http.sys that allows for remote code execution.

Record
CVE-2021-31166
Weakness
CWE-416
Updated
2026-11-02
NVD 9.8

HTTP Protocol Stack Remote Code Execution Vulnerability

Record
CVE-2021-31166
CVSS 3.1
9.8 CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS 2.0
7.5 HighAV:N/AC:L/Au:N/C:P/I:P/A:P
Weakness
CWE-416
Updated
2026-11-02

Affected products

Public exploits

Links only. Every CVE stores no exploit code.

Public exploits
SourceLinkDate
PoC in GitHub0vercl0k/CVE-2021-311662021-05-16
PoC in GitHubcorelight/CVE-2021-311662021-05-17
PoC in GitHubmvlnetdev/CVE-2021-31166-detection-rules2021-05-17
PoC in GitHubzha0gongz1/CVE-2021-311662021-05-17
PoC in GitHubzecopro/CVE-2021-311662021-05-19
PoC in GitHubbgsilvait/WIn-CVE-2021-311662021-05-23
PoC in GitHuby0g3sh-99/CVE-2021-31166-Exploit2021-07-03
PoC in GitHubZZ-SOCMAP/CVE-2021-311662021-09-27
PoC in GitHubiranzai/CVE-2021-31166-exploit2021-10-20
PoC in GitHubmauricelambert/CVE-2021-311662022-03-07
PoC in GitHub0xmaximus/Home-Demolisher2022-11-22
PoC in GitHubtesterxma/cve-2021-31166-poc2026-10-24
MetasploitWindows IIS HTTP Protocol Stack DOS2021-05-11

History

History
RecordedChangedSources
exploitation, exploits
first indexedCVE List, EUVD, GitHub Advisories, CISA KEV, Metasploit, NVD, PoC in GitHub

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-31166 is a critical vulnerability (CVSS 9.8) in Microsoft Http Protocol Stack, published May 11, 2021. CISA lists it as known to be exploited, since April 6, 2022. EUVD reports exploitation since April 6, 2022. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 99.9%, the 99th percentile. No source names a fixed version.

References

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