CVE-2026-6686

medium

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.

References

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

https://thehackernews.com/2026/07/unpatched-flaws-disclosed-in-filesystem.html

https://www.runzero.com/blog/fatfs-bugs/

https://github.com/runZeroInc/vulns-2026-fatfs-chance

https://elm-chan.org/fsw/ff/

Details

Source: Mitre, NVD

Published: 2026-07-01

Updated: 2026-07-02

Risk Information

CVSS v2

Base Score: 4.9

Vector: CVSS2#AV:L/AC:L/Au:N/C:C/I:N/A:N

Severity: Medium

CVSS v3

Base Score: 4.6

Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Severity: Medium

EPSS

EPSS: 0.00163