CVE-2026-6685

FatFs Integer Underflow in Dirty-Sector Cache Flush

CVSS 6.1 MEDIUMCWE-191

Vexday Risk Score

10Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 6.1EPSS —KEV nãoPoC —Nuclei —Metasploit —Patch —

Lifecycle

01 Jul 2026Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

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.

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

Affected products

ChaN · FatFs

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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/