CVE-2026-6688: Elm-Chan Fatfs

High severity, CVSS 7.6. EPSS: 0.3% chance of exploitation in the next 30 days.

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.

Affected products

• Elm-Chan Fatfs: up to and including r0.16

Published 2026-07-01. Last modified 2026-07-02.