CVE-2021-31166
CriticalExploitedPublic exploitHTTP Protocol Stack Remote Code Execution Vulnerability
Published May 11, 2021 · Updated Oct 30, 2025
Key Facts
Patch immediately- CVE-2021-31166 is a critical-severity vulnerability (CVSS 9.8 v3.1) affecting Windows 10 1809 (Microsoft), Windows 10 2004 (Microsoft), windows 10 20H2 (Microsoft) and 2 more products.
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Mar 24, 2022 and is known to be used in ransomware campaigns. Public exploit code is available.
- EPSS estimates a 100% probability of exploitation in the next 30 days.
- Fixed versions are available, including Windows 10 1809 10.0.19041.982, Windows 10 2004 10.0.19041.982, windows 10 20H2 10.0.19042.982.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
100%
Higher than 99.9% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings, used by ransomware
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2021-31166 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
Description
HTTP Protocol Stack Remote Code Execution Vulnerability
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Apr 6, 2022 | Apr 27, 2022 | Not reported |
| Industry KEV feed | Mar 24, 2022 | Apr 27, 2022 | Known |
| CIRCL KEV | Apr 6, 2022 | Apr 27, 2022 | Not reported |
| ENISA EUVD | Apr 6, 2022 | n/a | Not reported |
Required action: Apply updates per vendor instructions.
Affected Products
9 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| Windows 10 1809Microsoft | 10.0.19041.982 | 10.0.19041.982 |
| Windows 10 2004Microsoft | See advisory | 10.0.19041.982 |
| windows 10 20H2Microsoft | 10.0.19042.982 | 10.0.19042.982 |
| Windows Server 2004Microsoft | 10.0.19041.982 | 10.0.19041.982 |
| windows server 20H2Microsoft | 10.0.19042.982 | 10.0.19042.982 |
Patched Releases
Windows 10 1809
10.0.19041.982
Windows 10 2004
10.0.19041.982
windows 10 20H2
10.0.19042.982
Windows Server 2004
10.0.19041.982
windows server 20H2
10.0.19042.982
Timeline
Publicly disclosed
May 11, 2021
Added to Industry KEV feed
Mar 24, 2022
Added to CISA KEV
Apr 6, 2022
Added to CIRCL KEV
Apr 6, 2022
Added to ENISA EUVD
Apr 6, 2022
Last updated
Oct 30, 2025
Weakness Type
- CWE-416 Use After Free
References
- advisoryhttp://packetstormsecurity.com/files/162722/Microsoft-HTTP-Protocol-Stack-Remote-Code-Execution.html
- patchhttps://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31166
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
FAQ
Common Questions.
HTTP Protocol Stack Remote Code Execution Vulnerability
Affected: Windows 10 1809 (Microsoft) versions 10.0.19041.982; Windows 10 2004 (Microsoft); windows 10 20H2 (Microsoft) versions 10.0.19042.982, among others. The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Mar 24, 2022 and is known to be used in ransomware campaigns.
Yes. It was added on Apr 6, 2022 with a federal remediation due date of Apr 27, 2022.
Public exploit code is available.
Fixed versions are available, including Windows 10 1809 10.0.19041.982, Windows 10 2004 10.0.19041.982, windows 10 20H2 10.0.19042.982.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
Is CVE-2021-31166 Running On Your Attack Surface?
Brandefense maps vulnerabilities like this one to your internet-facing assets and tells you exactly where to patch.
Request A Demo