CVE-2026-6688

HIGH 7.6

FatFs Buffer Overflow via Unbounded LFN Filename Copy

CVSS Score

7.6

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-120
Vendor	chan
Product	fatfs
Published	Jul 1, 2026
Last Updated	Jul 1, 2026

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CVSS v3 Breakdown

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

Attack Vector

Physical

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Affected Versions

ChaN / FatFs

0 ≤ R0.16

References

NVD ↗ CVE.org ↗ EPSS Data ↗

runzero.com: https://www.runzero.com/blog/fatfs-bugs/ github.com: https://github.com/runZeroInc/vulns-2026-fatfs-chance elm-chan.org: https://elm-chan.org/fsw/ff/ runzero.com: https://www.runzero.com/advisories/fatfs-long-fn-of-downstream-cve-2026-6688/

Credits

HD Moore of runZero, Inc. Tod Beardsley of runZero, Inc.