CVE-2026-6686 MEDIUM

CVE-2026-6686: FatFs Use of Uninitialized Clusters After Seek Past EOF

Vendor Chan
Product FatFs
Weakness CWE-908
Published July 1, 2026
Last update July 1, 2026
View on NVD All CVEs

CVSS base score

4.6/10
Attack vector Physical
Attack complexity Low
Privileges required None
User interaction None
Confidentiality High
Integrity None

CVSS vector

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

What the vulnerability does

01Description

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.

Key dates

02Disclosure timeline

July 1, 2026 CVE published
July 1, 2026 Record updated