CVE-2026-6686FatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files beyond EOF without zero-filling newly allocated clusters.
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 4.6 MEDIUM (v3.1, NVD)CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- Weakness (CWE)
- CWE-908
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Not given
- NVD analysis
- Analyzed
- Record last updated
- Jul 2, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
elm-chan fatfs elm-chan:fatfs | through r0.16 | NVD |
References
- https://elm-chan.org/fsw/ff/product
- https://github.com/runZeroInc/vulns-2026-fatfs-chancethird-party-advisory, exploit
- https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/third-party-advisory
- https://www.runzero.com/blog/fatfs-bugs/third-party-advisory, exploit
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.