CVE-2026-6686

mediumCVSS 4.6covered by 1 sourcefirst seen 2026-07-01

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.

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Exploitation outlook

Low exploitation risk0.18% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 7% of all EPSS-scored CVEs.

Advisory coverage (1)

mediumCVE-2026-6686: FatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files…nvd · 2026-07-01

External references

NVD record for CVE-2026-6686

CVE.org record

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