CVE-2021-43226

CRITICALNVD 7.89.0▲
EchelonGraph scoreHIGH confidence

Score elevated to 9.0 because this CVE is listed on the CISA Known Exploited Vulnerabilities catalog (added 2025-10-06), indicating real-world exploitation has been confirmed by US federal agencies. NVD baseline CVSS 7.8 retained for reference. Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: cisa_kev, epss, ghsa, nvd
Trending — 5 sources updated this weekExploited in the wild
9.0EG
EchelonGraph verdictPatch nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV)
CISA-KEV: ExploitedEPSS PROB: 3%CVSS: 7.8Exploit: cisa kev · ssvc active · kev ransomware · public exploitExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Windows Common Log File System Driver Elevation of Privilege Vulnerability

CVSS v3
7.8
EG Score
9.0(high)
EG Risk
81(Attend)
EG Risk 81/100SSVC: Attend

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity90% × 45%
Exploitation100% × 40%
Automatability0% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
3%
EPSS %ILE
87%
KEV
⚠ Exploited

Published

December 15, 2021

Last Modified

August 22, 2026

Advisory Details (2)

Auto-updated Jun 4, 2026
⚠️ Active exploitation confirmed. Patch available. Sources: microsoft, cisa.
cisa Patch Available🔴 Active Exploitation

Known Exploited Vulnerabilities Catalog | CISA

Known Exploited Vulnerabilities Catalog | CISA. Listed in CISA Known Exploited Vulnerabilities catalog.

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-43226
microsoft Patch Available

Security Update Guide - Microsoft Security Response Center

Security Update Guide - Microsoft Security Response Center. Patch available via Microsoft Security Update

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-43226

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(1)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 97× in last 7d / 394× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 1,479 total refreshes for this CVE.

  1. 2026-09-25 10:58 UTCGHSA enrichment
  2. 2026-09-25 06:36 UTCVendor advisory
  3. 2026-09-25 06:36 UTCGHSA enrichment
  4. 2026-09-25 02:14 UTCVendor advisory
  5. 2026-09-25 02:14 UTCGHSA enrichment
  6. 2026-09-24 21:52 UTCVendor advisory
  7. 2026-09-24 21:51 UTCGHSA enrichment
  8. 2026-09-24 19:31 UTCCISA KEV update
  9. 2026-09-24 17:29 UTCEG score recompute
  10. 2026-09-24 17:29 UTCVendor advisory
  11. 2026-09-24 17:29 UTCGHSA enrichment
  12. 2026-09-24 14:00 UTCEPSS rescore
  13. 2026-09-24 14:00 UTCEPSS rescore
  14. 2026-09-24 13:07 UTCVendor advisory
  15. 2026-09-24 13:07 UTCGHSA enrichment
  16. 2026-09-24 08:45 UTCVendor advisory
  17. 2026-09-24 08:45 UTCGHSA enrichment
  18. 2026-09-24 04:23 UTCVendor advisory
  19. 2026-09-24 04:23 UTCGHSA enrichment
  20. 2026-09-24 00:00 UTCVendor advisory
  21. 2026-09-24 00:00 UTCGHSA enrichment
  22. 2026-09-23 19:38 UTCVendor advisory
  23. 2026-09-23 19:38 UTCGHSA enrichment
  24. 2026-09-23 15:17 UTCEG score recompute
  25. 2026-09-23 15:17 UTCVendor advisory
Show 75 more
  1. 2026-09-23 15:17 UTCGHSA enrichment
  2. 2026-09-23 13:44 UTCEPSS rescore
  3. 2026-09-23 10:55 UTCVendor advisory
  4. 2026-09-23 10:55 UTCGHSA enrichment
  5. 2026-09-23 06:33 UTCVendor advisory
  6. 2026-09-23 06:33 UTCGHSA enrichment
  7. 2026-09-23 02:11 UTCVendor advisory
  8. 2026-09-23 02:11 UTCGHSA enrichment
  9. 2026-09-22 21:49 UTCVendor advisory
  10. 2026-09-22 21:49 UTCGHSA enrichment
  11. 2026-09-22 19:36 UTCCISA KEV update
  12. 2026-09-22 17:27 UTCEG score recompute
  13. 2026-09-22 17:27 UTCVendor advisory
  14. 2026-09-22 17:27 UTCGHSA enrichment
  15. 2026-09-22 14:44 UTCEPSS rescore
  16. 2026-09-22 12:59 UTCVendor advisory
  17. 2026-09-22 12:59 UTCGHSA enrichment
  18. 2026-09-22 08:37 UTCVendor advisory
  19. 2026-09-22 08:37 UTCGHSA enrichment
  20. 2026-09-22 04:15 UTCVendor advisory
  21. 2026-09-22 04:15 UTCGHSA enrichment
  22. 2026-09-21 23:53 UTCEG score recompute
  23. 2026-09-21 23:53 UTCVendor advisory
  24. 2026-09-21 23:53 UTCGHSA enrichment
  25. 2026-09-21 20:28 UTCEPSS rescore
  26. 2026-09-21 19:31 UTCVendor advisory
  27. 2026-09-21 19:31 UTCGHSA enrichment
  28. 2026-09-21 19:09 UTCCISA KEV update
  29. 2026-09-21 15:09 UTCVendor advisory
  30. 2026-09-21 15:09 UTCGHSA enrichment
  31. 2026-09-21 10:47 UTCVendor advisory
  32. 2026-09-21 10:47 UTCGHSA enrichment
  33. 2026-09-21 06:25 UTCVendor advisory
  34. 2026-09-21 06:25 UTCGHSA enrichment
  35. 2026-09-21 02:03 UTCVendor advisory
  36. 2026-09-21 02:03 UTCGHSA enrichment
  37. 2026-09-20 21:41 UTCEG score recompute
  38. 2026-09-20 21:41 UTCVendor advisory
  39. 2026-09-20 21:41 UTCGHSA enrichment
  40. 2026-09-20 20:13 UTCEPSS rescore
  41. 2026-09-20 17:19 UTCVendor advisory
  42. 2026-09-20 17:19 UTCGHSA enrichment
  43. 2026-09-20 12:57 UTCVendor advisory
  44. 2026-09-20 12:57 UTCGHSA enrichment
  45. 2026-09-20 08:33 UTCVendor advisory
  46. 2026-09-20 08:33 UTCGHSA enrichment
  47. 2026-09-20 04:11 UTCVendor advisory
  48. 2026-09-20 04:10 UTCGHSA enrichment
  49. 2026-09-19 23:49 UTCVendor advisory
  50. 2026-09-19 23:49 UTCGHSA enrichment
  51. 2026-09-19 19:27 UTCEG score recompute
  52. 2026-09-19 19:27 UTCVendor advisory
  53. 2026-09-19 19:27 UTCGHSA enrichment
  54. 2026-09-19 15:38 UTCEPSS rescore
  55. 2026-09-19 15:05 UTCVendor advisory
  56. 2026-09-19 15:05 UTCGHSA enrichment
  57. 2026-09-19 10:42 UTCVendor advisory
  58. 2026-09-19 10:42 UTCGHSA enrichment
  59. 2026-09-19 06:18 UTCVendor advisory
  60. 2026-09-19 06:18 UTCGHSA enrichment
  61. 2026-09-19 01:56 UTCVendor advisory
  62. 2026-09-19 01:56 UTCGHSA enrichment
  63. 2026-09-18 21:34 UTCEG score recompute
  64. 2026-09-18 21:34 UTCVendor advisory
  65. 2026-09-18 21:34 UTCGHSA enrichment
  66. 2026-09-18 19:23 UTCEPSS rescore
  67. 2026-09-18 19:20 UTCCISA KEV update
  68. 2026-09-18 17:12 UTCVendor advisory
  69. 2026-09-18 17:12 UTCGHSA enrichment
  70. 2026-09-18 14:15 UTCCISA KEV update
  71. 2026-09-18 12:50 UTCVendor advisory
  72. 2026-09-18 12:50 UTCGHSA enrichment
  73. 2026-09-18 08:27 UTCVendor advisory
  74. 2026-09-18 08:27 UTCGHSA enrichment
  75. 2026-09-18 04:05 UTCVendor advisory

Publicly available exploits

(1 reference)

Working exploit code is in the public domain (1 GitHub PoC). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCRosayxy/cve-2021-43226PoC
    First seen Oct 30, 2023

    a Proof of Concept of cve-2021-43226,stack overflow in Windows driver clfs.sys

    Open source ↗

Related CVEs(same CWE)

Frequently asked(6)

What is CVE-2021-43226?
CVE-2021-43226 is a critical vulnerability published on December 15, 2021. Windows Common Log File System Driver Elevation of Privilege Vulnerability
When was CVE-2021-43226 disclosed?
CVE-2021-43226 was first published in the National Vulnerability Database on December 15, 2021, with the most recent update on August 22, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-43226 actively exploited?
Yes. CISA added CVE-2021-43226 to the Known Exploited Vulnerabilities catalog on October 6, 2025, affecting Microsoft Windows. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.
What is the CVSS score of CVE-2021-43226?
CVE-2021-43226 has a CVSS v3 base score of 7.8 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.
Which products are affected by CVE-2021-43226?
CVE-2021-43226 affects Microsoft Windows. The full affected-products list, including version ranges and fixed versions, is shown in the Affected Packages section of this page.
How do I remediate CVE-2021-43226?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-43226, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2021-43226

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