CVE-2026-6686 PUBLISHED

FatFs Use of Uninitialized Clusters After Seek Past EOF

Assigner: runZero
Reserved: 20.04.2026 Published: 01.07.2026 Updated: 01.07.2026

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.

Metrics

CVSS Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CVSS Score: 4.6

Product Status

Vendor ChaN
Product FatFs
Versions Default: unaffected
  • affected from 0 to R0.16 (incl.)

Credits

  • HD Moore of runZero, Inc. finder
  • Tod Beardsley of runZero, Inc. coordinator

References

Problem Types

  • CWE-908 Use of uninitialized resource CWE