CVE-2026-6686
FatFs Use of Uninitialized Clusters After Seek Past EOF
- Published
- Jul 1, 2026
- Updated
- Jul 1, 2026
- Assigning CNA
- runZero
- Evidence observed
- Aug 16, 2026
Primary CVSS
nvd · CVSS 3.1
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:NLow · next 30 days
- Percentile
- 17.4%
- Model date
- Sep 21, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
Summary
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.
Sources
1- vulns-2026-fatfs-chanceResearch
Documented security vulnerabilities in the FatFs embedded filesystem library with CVE details, fuzzing harness, exploit disk-image generator, and supply-chain impact analysis across dozens of downstream firmware projects.
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