Medium severity4.6NVD Advisory· Published Jul 1, 2026· Updated Jul 2, 2026
CVE-2026-6686
CVE-2026-6686
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
2Patches
Vulnerability mechanics
References
3- www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/nvdThird Party Advisory
- www.runzero.com/blog/fatfs-bugs/nvdThird Party AdvisoryExploit
- elm-chan.org/fsw/ff/nvdProduct
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