CVE-2026-83991

MEDIUMPre-NVD 5.55.5—
EchelonGraph scoreHIGH confidence

Score 5.5 from GitHub Security Advisory published 2026-09-08. the CNA's CVSS baseline 5.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: cna:microsoft, epss, ghsa
Trending — 4 sources updated this weekElevated
5.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.5Exploit: Elevated riskExposed: 0

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

Missing authentication for critical function in Windows Cloud Files Mini Filter Driver allows an authorized attacker to perform tampering locally.

CVSS v3
5.5
EG Score
5.5(high)
EG Risk
41(Track)
EG Risk 41/100SSVC: Track

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
Severity55% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
28%
KEV
Not listed

Published

September 8, 2026

Last Modified

September 18, 2026

Advisory Details (1)

Auto-updated Sep 9, 2026
Patch available. Sources: microsoft.
microsoft Patch Available

Security Update Guide - Microsoft Security Response Center

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

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-83991

Vendor Advisories for CVE-2026-83991(2)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 38× in last 7d / 76× 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.

  1. 2026-09-20 20:16 UTCEPSS rescore
  2. 2026-09-20 19:16 UTCVendor advisory
  3. 2026-09-20 19:16 UTCGHSA enrichment
  4. 2026-09-19 20:11 UTCEG score recompute
  5. 2026-09-19 20:11 UTCVendor advisory
  6. 2026-09-19 20:11 UTCGHSA enrichment
  7. 2026-09-18 21:06 UTCEG score recompute
  8. 2026-09-18 21:06 UTCVendor advisory
  9. 2026-09-18 21:06 UTCGHSA enrichment
  10. 2026-09-18 19:28 UTCEPSS rescore
  11. 2026-09-18 14:12 UTCVendor advisory
  12. 2026-09-18 14:12 UTCGHSA enrichment
  13. 2026-09-17 23:06 UTCVendor advisory
  14. 2026-09-17 23:06 UTCGHSA enrichment
  15. 2026-09-17 20:11 UTCVendor advisory
  16. 2026-09-17 20:11 UTCGHSA enrichment
  17. 2026-09-17 19:55 UTCEG score recompute
  18. 2026-09-17 19:55 UTCVendor advisory
  19. 2026-09-17 19:55 UTCGHSA enrichment
  20. 2026-09-17 19:32 UTCEPSS rescore
  21. 2026-09-16 22:12 UTCVendor advisory
  22. 2026-09-16 22:12 UTCGHSA enrichment
  23. 2026-09-16 21:52 UTCEG score recompute
  24. 2026-09-16 21:52 UTCVendor advisory
  25. 2026-09-16 21:52 UTCGHSA enrichment
Show 51 more
  1. 2026-09-16 14:09 UTCEPSS rescore
  2. 2026-09-16 05:15 UTCEPSS rescore
  3. 2026-09-15 22:47 UTCVendor advisory
  4. 2026-09-15 22:47 UTCGHSA enrichment
  5. 2026-09-15 18:00 UTCEG score recompute
  6. 2026-09-15 18:00 UTCVendor advisory
  7. 2026-09-15 17:59 UTCGHSA enrichment
  8. 2026-09-15 03:12 UTCEPSS rescore
  9. 2026-09-15 03:12 UTCEPSS rescore
  10. 2026-09-14 22:57 UTCVendor advisory
  11. 2026-09-14 22:57 UTCGHSA enrichment
  12. 2026-09-14 17:49 UTCVendor advisory
  13. 2026-09-14 17:49 UTCGHSA enrichment
  14. 2026-09-13 21:10 UTCEG score recompute
  15. 2026-09-13 21:10 UTCVendor advisory
  16. 2026-09-13 21:10 UTCGHSA enrichment
  17. 2026-09-12 22:05 UTCEG score recompute
  18. 2026-09-12 22:05 UTCVendor advisory
  19. 2026-09-12 22:05 UTCGHSA enrichment
  20. 2026-09-11 22:58 UTCVendor advisory
  21. 2026-09-11 22:58 UTCGHSA enrichment
  22. 2026-09-11 20:06 UTCVendor advisory
  23. 2026-09-11 20:06 UTCGHSA enrichment
  24. 2026-09-11 17:03 UTCEG score recompute
  25. 2026-09-11 17:03 UTCVendor advisory
  26. 2026-09-11 17:03 UTCGHSA enrichment
  27. 2026-09-10 23:37 UTCGHSA enrichment
  28. 2026-09-10 21:24 UTCEG score recompute
  29. 2026-09-10 21:24 UTCGHSA enrichment
  30. 2026-09-09 22:19 UTCEG score recompute
  31. 2026-09-09 22:19 UTCGHSA enrichment
  32. 2026-09-09 20:49 UTCEG score recompute
  33. 2026-09-09 20:49 UTCVendor advisory
  34. 2026-09-09 20:49 UTCGHSA enrichment
  35. 2026-09-09 20:09 UTCEG score recompute
  36. 2026-09-09 20:09 UTCVendor advisory
  37. 2026-09-09 20:09 UTCGHSA enrichment
  38. 2026-09-09 19:30 UTCEG score recompute
  39. 2026-09-09 19:30 UTCVendor advisory
  40. 2026-09-09 19:30 UTCGHSA enrichment
  41. 2026-09-09 18:40 UTCEG score recompute
  42. 2026-09-09 18:40 UTCVendor advisory
  43. 2026-09-09 18:40 UTCGHSA enrichment
  44. 2026-09-08 23:44 UTCEG score recompute
  45. 2026-09-08 23:44 UTCVendor advisory
  46. 2026-09-08 23:43 UTCGHSA enrichment
  47. 2026-09-08 18:57 UTCEG score recompute
  48. 2026-09-08 18:57 UTCGHSA enrichment
  49. 2026-09-08 17:55 UTCEG score recompute
  50. 2026-09-08 17:55 UTCVendor advisory
  51. 2026-09-08 17:25 UTCMITRE cvelistV5first tracked

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 PoCkarollooool/CVE-2026-83991-writeup-and-poc
    First seen Sep 9, 2026

    CVE-2026-83991: Windows Cloud Files access-check bypass

    Open source ↗

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-83991?
CVE-2026-83991 is a medium vulnerability published on September 8, 2026. Missing authentication for critical function in Windows Cloud Files Mini Filter Driver allows an authorized attacker to perform tampering locally.
When was CVE-2026-83991 disclosed?
CVE-2026-83991 was first published in the National Vulnerability Database on September 8, 2026, with the most recent update on September 18, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-83991 actively exploited?
CVE-2026-83991 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 72.3% of all scored CVEs.
What is the CVSS score of CVE-2026-83991?
CVE-2026-83991 has a CVSS v4.0 base score of 5.5 (CNA self-assessment; NVD's own analysis pending).
How do I remediate CVE-2026-83991?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-83991, 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-2026-83991

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