CVE-2021-31166

highpriority · act · 90OT risk · criticalKEV · exploitedEPSS 0.999 · 100 %ileexploit · functionalEURUUS

grimoire priorityP0 · Act now

Exploitable?

Yes · in the wild

CISA KEV · 13 exploits · functional

Likely / severe?

99.9% (100th) EPSS

CVSS 7.5 · high

Is it mine?

12 products

Check your exposure

Who says so?

4 sources

cnnvd · enisa_euvd · fstec_bdu · nvd

added 2022-04-06remediate by 2022-04-27

required action Apply updates per vendor instructions.

EPSS · scored 2026-10-27

Microsoft HTTP Protocol Stack Remote Code Execution Vulnerability

HTTP Protocol Stack Remote Code Execution Vulnerability

cvss

Technical severity, 0–10. One row per scoring source.

9.8

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · high–critical · 7.5–9.8

v2.07.5highAV:N/AC:L/Au:N/C:P/I:P/A:Pprimary · NVD / NIST USexploitability 10 · impact 6.4

v2.07.5highAV:N/AC:L/Au:N/C:P/I:P/A:P/E:Hsecondary · CVSS-BT (t0sche)

v3.19.8criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · NVD / NIST USexploitability 3.9 · impact 5.9

v3.19.8criticalAV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · FSTEC (BDU) RU

v3.19.8criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:Csecondary · ENISA EU

v3.19.8criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · secure@microsoft.com USexploitability 3.9 · impact 5.9

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Exploitation: active · Automatable: yes · Technical Impact: totalcoordinatorcisa_ssvcUS

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-416USprimaryCWE-416US

ATT&CK techniques

ATT&CK techniques this enables or maps to.

exploits (13)

Public proof-of-concept and weaponised exploit code.

auxiliary/dos/windows/http/http_sys_accept_encoding_dos_cve_2021_31166Windows IIS HTTP Protocol Stack DOSfunctional · metasploit
0vercl0k/CVE-2021-31166Proof of concept for CVE-2021-31166, a remote HTTP.sys use-after-free triggered remotely.PoC · poc_in_github
0xmaximus/Home-DemolisherPoC for CVE-2021-31166 and CVE-2022-21907PoC · poc_in_github
ZZ-SOCMAP/CVE-2021-31166Windows HTTP协议栈远程代码执行漏洞 CVE-2021-31166PoC · poc_in_github
bgsilvait/WIn-CVE-2021-31166bgsilvait/WIn-CVE-2021-31166PoC · poc_in_github
corelight/CVE-2021-31166HTTP Protocol Stack CVE-2021-31166PoC · poc_in_github

affected products (12)

Products and version ranges known to be affected.

Microsoft Windows 10 Version 200410.0.0 → 10.0.19041.982enisa_euvdEU
Microsoft Windows 10 Version 20H210.0.0 → 10.0.19042.982enisa_euvdEU
Microsoft Windows Server version 200410.0.0 → 10.0.19041.982enisa_euvdEU
Microsoft Windows Server version 20H210.0.0 → 10.0.19042.982enisa_euvdEU
Microsoft Corp Windows 10 2004all versionsfstec_bduRU
Microsoft Corp Windows 10 20H2all versionsfstec_bduRU
Microsoft Corp Windows Server 2004 (Server Core Installation)all versionsfstec_bduRU
Microsoft Corp Windows Server 20H2 (Server Core Installation)all versionsfstec_bduRU
microsoft windows 10 2004< 10.0.19041.982nvdUScpe:2.3:o:microsoft:windows_10_2004:*:*:*:*:*:*:*:*
microsoft windows 10 20h2< 10.0.19042.982nvdUScpe:2.3:o:microsoft:windows_10_20h2:*:*:*:*:*:*:*:*
microsoft windows server 2004< 10.0.19041.982nvdUScpe:2.3:o:microsoft:windows_server_2004:*:*:*:*:*:*:*:*
microsoft windows server 20h2< 10.0.19042.982nvdUScpe:2.3:o:microsoft:windows_server_20h2:*:*:*:*:*:*:*:*

also known as (4)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd fstec_bdu nvd NVD CVE.org MITRE

published 2021-05-11modified 2026-06-17

related (12,235)

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+12230 more

references (10)

External citations — patches, advisories, analysis.

scry

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