CVE-2026-6686

MEDIUMPre-NVD 4.64.6—
EchelonGraph scoreHIGH confidence

Score 4.6 from GitHub Security Advisory published 2026-07-01. a secondary CVSS source baseline 4.6; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this week
4.6
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 4.6Exploit: NoneExposed: 0

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

FatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files beyond EOF without zero-filling newly allocated clusters. This maps to CWE-908 (Use of Uninitialized Resource). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (4.6, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Partial.

CVSS v3
4.6
EG Score
4.6(high)
EPSS
7.4%
KEV
Not listed

Published

July 1, 2026

Last Modified

July 2, 2026

Advisory Details (3)

Auto-updated Jul 3, 2026
⚠️ Active exploitation confirmed. No patch confirmed yet.
generic

GitHub - runZeroInc/vulns-2026-fatfs-chance · GitHub

https://github.com/runZeroInc/vulns-2026-fatfs-chance
generic🔴 Active Exploitation

Seven FatFs bugs, one very large blast radius

https://www.runzero.com/blog/fatfs-bugs/
generic🔴 Active Exploitation

FatFS uninitialized cluster exposure after seek beyond EOF

https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/

Vendor Advisories for CVE-2026-6686(1)

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 22× in last 7d / 22× 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. 2026-07-07 03:26 UTCEG score recompute
  2. 2026-07-07 03:25 UTCGHSA enrichment
  3. 2026-07-06 16:27 UTCEPSS rescore
  4. 2026-07-06 16:27 UTCEPSS rescore
  5. 2026-07-06 05:33 UTCEG score recompute
  6. 2026-07-06 05:33 UTCGHSA enrichment
  7. 2026-07-06 02:23 UTCEPSS rescore
  8. 2026-07-06 02:23 UTCEPSS rescore
  9. 2026-07-05 07:40 UTCEG score recompute
  10. 2026-07-05 07:39 UTCGHSA enrichment
  11. 2026-07-05 02:31 UTCEPSS rescore
  12. 2026-07-05 02:30 UTCEPSS rescore
  13. 2026-07-04 09:46 UTCEG score recompute
  14. 2026-07-04 09:45 UTCGHSA enrichment
  15. 2026-07-04 06:31 UTCEPSS rescore
  16. 2026-07-04 06:31 UTCEPSS rescore
  17. 2026-07-03 11:52 UTCEG score recompute
  18. 2026-07-03 11:52 UTCGHSA enrichment
  19. 2026-07-02 13:55 UTCEG score recompute
  20. 2026-07-02 13:55 UTCGHSA enrichment
  21. 2026-07-01 16:03 UTCEG score recompute
  22. 2026-07-01 16:02 UTCGHSA enrichment

Frequently asked(5)

What is CVE-2026-6686?
CVE-2026-6686 is a medium vulnerability published on July 1, 2026. FatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files beyond EOF without zero-filling newly allocated clusters. This maps to CWE-908 (Use of Uninitialized Resource). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (4.6, Medium). The…
When was CVE-2026-6686 disclosed?
CVE-2026-6686 was first published in the National Vulnerability Database on July 1, 2026, with the most recent update on July 2, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-6686 actively exploited?
CVE-2026-6686 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 7.4% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-6686?
CVE-2026-6686 has a CVSS v3 base score of 4.6 (NVD).
How do I remediate CVE-2026-6686?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-6686, 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-2026-6686

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