CVE-2026-6685

FatFs R0.16 and earlier exhibits a stale dirty-cache skip via unsigned-subtraction wrap in f_read() / f_write() (fp->sect - sect < cc) during interleaved read/write on fragmented filesystems. This maps to CWE-191 (Integer Underflow). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H (6.1, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total.
Wrap or Wraparound
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
NISTPrimary
6.1 MEDIUM
PHYSICAL
LOW
NONE
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Awaiting analysis
This vulnerability is currently awaiting analysis.
Base Score
CVSS 3.x
EPSS Score
Percentile: Unknown
Common Weakness Enumeration
References
https://elm-chan.org/fsw/ff/
https://github.com/runZeroInc/vulns-2026-fatfs-chance
https://www.runzero.com/advisories/fatfs-unsigned-sub-wrap-cve-2026-6685/
https://www.runzero.com/blog/fatfs-bugs/
https://github.com/runZeroInc/vulns-2026-fatfs-chance