CVE-2026-6686CWE-908

FatFs Use of Uninitialized Clusters After Seek Past EOF

Medium · published July 1, 2026

CVSS v3.1
4.6
EPSS
0%
Percentile
16.1
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
4.6 · MEDIUM
Vector
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CVSS v4.0
Not supplied
EPSS
0.00255 · 16.1th percentile
Weakness
CWE-908 · Use of Uninitialized Resource
Published
2026-07-01T13:55Z
EPSS history
Timeline
  • 01 JUL 13:55Z
    FatFs Use of Uninitialized Clusters After Seek Past EOF
    cvelistv5