CVE-2026-6688

FatFs Buffer Overflow via Unbounded LFN Filename Copy

CVSS 7.6 HIGHCWE-120

Vexday Risk Score

18Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 7.6EPSS —KEV nãoPoC —Nuclei —Metasploit —Patch —

Lifecycle

01 Jul 2026Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

FatFs R0.16 and earlier contains a downstream-caller vulnerability pattern associated with FatFs long filename handling. With LFN enabled, fno.fname can be up to 255 characters; many callers copy it into short fixed buffers without bounds checks, causing overflow. This maps to CWE-120 (Buffer Copy without Checking Size of Input). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H (7.6, High). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total.

CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/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-long-fn-of-downstream-cve-2026-6688/https://www.runzero.com/blog/fatfs-bugs/