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Critical 9.8Known exploited (CISA KEV)Published May 11, 2021
CVE-2021-31166HTTP Protocol Stack Remote Code Execution Vulnerability
Updated under an hour ago ()
Does this affect you?
It affects Microsoft Windows 10 Version 2004 and 4 other products. Add what you run to find out whether that includes you.
CISA lists it as known exploited since Apr 6, 2022; federal agencies had to remediate by Apr 27, 2022. Treat that date as your deadline.
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HTTP Protocol Stack Remote Code Execution Vulnerability
- CVSS
- 9.8 CRITICAL (v3.1, CNA)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
- Weakness (CWE)
- CWE-416
- Known exploited
- Added to CISA KEV Apr 6, 2022; federal remediation due Apr 27, 2022Apply updates per vendor instructions.
- EPSS (exploitation in the next 30 days)
- 99.87% (percentile 100)
- Assigned by
- microsoft
- NVD analysis
- Analyzed
- Record last updated
- Oct 21, 2025
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Microsoft Windows 10 Version 2004 microsoft:windows_10_1809 | from 10.0.0 before 10.0.19041.982 | CNA record |
Microsoft Windows Server version 2004 microsoft:windows_server_2004 | from 10.0.0 before 10.0.19041.982 | CNA record |
Microsoft Windows 10 Version 20H2 microsoft:windows_10_20h2 | from 10.0.0 before 10.0.19042.982 | CNA record |
Microsoft Windows Server version 20H2 microsoft:windows_server_20h2 | from 10.0.0 before 10.0.19042.982 | CNA record |
microsoft windows_10_2004 microsoft:windows_10_2004 | before 10.0.19041.982 | NVD |
microsoft windows_10_20h2 microsoft:windows_10_20h2 | before 10.0.19042.982 | NVD |
microsoft windows_server_2004 microsoft:windows_server_2004 | before 10.0.19041.982 | NVD |
microsoft windows_server_20h2 microsoft:windows_server_20h2 | before 10.0.19042.982 | NVD |
References
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31166x-refsource-misc, patch, vendor-advisory
- http://packetstormsecurity.com/files/162722/Microsoft-HTTP-Protocol-Stack-Remote-Code-Execution.htmlx-refsource-misc, third-party-advisory, vdb-entry
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31166us-government-resource
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.