CISA KEV entry
CVE-2021-31166Microsoft HTTP Protocol Stack Remote Code Execution Vulnerability
Microsoft HTTP Protocol Stack. Added to the CISA Known Exploited Vulnerabilities catalogue on 6 April 2022.
Data status: a source is stale
Last synced CISA catalogue version 2026.11.04 (released 4 November 2026) 1,768 entries Updated manually
- Date added
- 2022-04-06
- Federal due date
- 2022-04-27 21 days after it was added; passed at the sync of 2026-11-05
- Known ransomware use
- Unknown
- Forensic triage (BOD 26-04)
- No
- CVSS
- 9.8 Critical CVSS 3.1, scored by secure@microsoft.com
- EPSS
- 99.86% percentile 99.9, scored 2026-11-04
- CISA SSVC
- Exploitation active, automatable yes, technical impact total
- NVD status
- Analyzed published 2021-05-11, 330 days before the KEV listing
BOD 26-04 remediation window
With CISA's SSVC answers for this CVE (automatable: yes, technical impact: total), BOD 26-04 Table 1 gives 3 days and forensic triage on a publicly exposed asset (row 1) and 3 days and forensic triage on an asset that is not publicly exposed (row 9) S06. The catalogue due date, 21 days after the date added, was set before BOD 26-04 took effect on 10 June 2026 S06. The directive binds US federal civilian executive branch agencies only.
What CISA says
Short description
Microsoft HTTP Protocol Stack contains a vulnerability in http.sys that allows for remote code execution.
Required action
Apply updates per vendor instructions.
Notes
https://nvd.nist.gov/vuln/detail/CVE-2021-31166
CWE in the catalogue
CWE-416
Official links
- CISA KEV catalogue entry cisa.gov
- NVD record nvd.nist.gov
Vendor advisory and patch links
References NVD tags Vendor Advisory or Patch, exactly as NVD lists them.
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31166 Patch, Vendor Advisory
Links in CISA's notes
NVD details
- CWE (NVD)
- CWE-416 by nvd@nist.gov
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H- CVSS versions in NVD
- V2, V31
- Last modified in NVD
- 2026-06-17T03:51:21.910
Where each value comes from
| Field | Source | Fetched, UTC | State |
|---|---|---|---|
| Catalogue fields | CISA KEV JSON, version 2026.11.04 | 2026-11-05 11:38 | current |
| NVD published, status, CVSS, CWE, vendor links | NVD CVE API 2.0; CVSS: NVD (secure@microsoft.com) | 2026-11-03 12:37 | current at 2026-11-05 11:38 |
| EPSS | FIRST EPSS API, scores of 2026-11-04 | 2026-11-05 11:38 | current |
| CISA SSVC | CISA ADP (via NVD), record of 2025-02-07 | 2026-11-03 12:37 | current |
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