Vulnerability Description
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 Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Elm-Chan | Fatfs | <= r0.16 |
Related Weaknesses (CWE)
References
- https://elm-chan.org/fsw/ff/Product
- https://github.com/runZeroInc/vulns-2026-fatfs-chanceThird Party AdvisoryExploit
- https://www.runzero.com/advisories/fatfs-long-fn-of-downstream-cve-2026-6688/Third Party Advisory
- https://www.runzero.com/blog/fatfs-bugs/Third Party AdvisoryExploit
- https://github.com/runZeroInc/vulns-2026-fatfs-chanceThird Party AdvisoryExploit
FAQ
What is CVE-2026-6688?
CVE-2026-6688 is a vulnerability with a CVSS score of 7.6 (HIGH). 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 i...
How severe is CVE-2026-6688?
CVE-2026-6688 has been rated HIGH with a CVSS base score of 7.6/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-6688?
Check the references section above for vendor advisories and patch information. Affected products include: Elm-Chan Fatfs.