PT-2026-54928 · Chan · Fatfs

Hd Moore + 1 · Published 2026-07-01 · Updated 2026-07-01 · CVE-2026-6686

NVD

CVSS v3.1

4.6

Medium

Base vector

AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

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.

Exploit

Fix

Use of Uninitialized Resource

Weakness Enumeration

CWE-908

Related Identifiers

CVE-2026-6686

Affected Products

Fatfs

References · 5

• 🔥 https://github.com/runZeroInc/vulns-2026-fatfs-chance · Exploit
• https://nvd.nist.gov/vuln/detail/CVE-2026-6686 · Security Note
• https://runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686 · Note
• https://elm-chan.org/fsw/ff · Note
• https://runzero.com/blog/fatfs-bugs · Note