Security readout for executives and security teams
CVE-2021-31166 is a critical Microsoft Windows HTTP Protocol Stack remote code execution flaw. It can be reached over the network without authentication or user interaction on affected systems. CISA lists it as known exploited, so organizations should treat unpatched, exposed Windows 10 and Windows Server 2004/20H2 assets as urgent. Exposure is most likely on affected Windows 10 or Windows Server 2004/20H2 systems where HTTP Protocol Stack functionality is reachable, especially internet-facing HTTP services. The bundle does not prove every listed Windows host is exploitable; validate OS version, patch level, and whether HTTP.sys-backed services are exposed. Immediate priority for exposed or mission-critical Windows systems. The vulnerability is critical, remotely reachable, requires no authentication, and is in CISA KEV. Patch verification should be tracked as an urgent remediation item. Mitigation focus: Apply Microsoft security guidance and updates for CVE-2021-31166.; Prioritize internet-facing affected Windows Server and Windows 10 assets.; Restrict external access to exposed HTTP.sys-backed services until patched..
Michael Williams reviewed this cited source version on .
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Open ATT&CK lookupExecution behavior lookup
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Open ATT&CK lookupCVE-2021-31166 mapping review
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Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.8 (3.1)
- Known Exploited
- Yes
- Published
Vector: 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
CNA and ADP enrichment extracted from CVE v5
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CISA KEV status
CVSS vector scores
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CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C3.95.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9.8CriticalVector: 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
Source materials
- CVE List V5 sourceCVE List V5
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31166CVE reference · x_refsource_MISC
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-31166CVE reference · government-resource
Products and packages named in the record
CWE details
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Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.