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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| ChaN | FatFs | ≤ R0.16 | — |
References
- https://www.runzero.com/blog/fatfs-bugs/ third-party-advisory
- https://github.com/runZeroInc/vulns-2026-fatfs-chance technical-description
- https://elm-chan.org/fsw/ff/ product
- https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/ third-party-advisory