CVE-2026-6686
FatFs Use of Uninitialized Clusters After Seek Past EOF
- State
- Published
- Severity
- 4.6 Medium
- Published
- Jul 1, 2026
- Updated
- Jul 1, 2026
- Reserved
- Apr 20, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 4.6 Medium | CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N | runZero |
Weaknesses
- CWE-908 Use of uninitialized resource
Affected Products
| Product | Versions |
|---|---|
FatFsChaN |
|
References
- https://www.runzero.com/blog/fatfs-bugs/third-party-advisory
- https://github.com/runZeroInc/vulns-2026-fatfs-chancetechnical-description
- https://elm-chan.org/fsw/ff/product
- https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/third-party-advisory
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