CVE-2026-6686 — Security Box Score

CVE · referencelatest edition

Reference page — cumulative record through Wednesday, August 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-6686MEDIUM

ChaN FatFs — FatFs Use of Uninitialized Clusters After Seek Past EOF

  AV  AC  PR  UI  S  C  I  A   CVSS    EPSS   %ile   KEV
   P   L   N   N  U  H  N  N    4.6   .0038   31.1     —

AFFECTED
  Product  Versions     Fixed
  FatFs    unspecified  —

TIMELINE
  Apr 20  Reserved by runZero
  Jul 1   EXPLOIT PUBLISHED — CVE-2026-6686 (ChaN FatFs). Public exploit reference added.
  Jul 1   Published (CNA: runZero)

CWE-908 · CNA: runZero · CVSS v3.1 · 4 references · NVD status: Analyzed

Description

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.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
April 20, 2026	Reserved	Reserved by runZero
July 1, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-6686 (ChaN FatFs). Public exploit reference added.
July 1, 2026	Published	Published (CNA: runZero)

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
ChaN	FatFs	—	—	—

Weaknesses

CWE-908

References (4)

https://elm-chan.org/fsw/ff/ [Product]
https://github.com/runZeroInc/vulns-2026-fatfs-chance [Third Party Advisory, Exploit]
https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/ [Third Party Advisory]
https://www.runzero.com/blog/fatfs-bugs/ [Third Party Advisory, Exploit]

Authoritative record: CVE-2026-6686 at cve.org

Vendors: chan

Weaknesses: CWE-908

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-6686 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Wednesday, August 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.