Vulnerability in Chan Fatfs
CVE-2026-6686
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 4.6 (Medium). Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.003 (15.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 15th percentile — 15.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000
Affected products
- Chan Fatfs — versions 0
- Elm-Chan Fatfs
Weakness classification (CWE)
References
- 44488dab-36db-4358-99f9-bc116477f914 (Exploit, Third Party Advisory, third-party-advisory)
- 44488dab-36db-4358-99f9-bc116477f914 (Exploit, technical-description, Third Party Advisory)
- 44488dab-36db-4358-99f9-bc116477f914 (Product, product)
- 44488dab-36db-4358-99f9-bc116477f914 (Third Party Advisory, third-party-advisory)
Frequently asked questions
- What is CVE-2026-6686?
- CVE-2026-6686 is a medium-severity vulnerability in Chan Fatfs, classified under Use of Uninitialized Resource. CVSS score: 4.6/10. Published 2026-07-01.
- How severe is CVE-2026-6686?
- Medium severity. CVSS v3 base score is 4.6 out of 10.