What is CVE-2026-6688?

CVE-2026-6688 is a high-severity vulnerability in Chan Fatfs, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 7.6/10. Published 2026-07-01.

How severe is CVE-2026-6688?

High severity. CVSS v3 base score is 7.6 out of 10.

Buffer overflow in Chan Fatfs

CVE-2026-6688

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.

Vulnerability class: Buffer Overflow

EPSS: 0.004 (35.1th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 7.6 (High). Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H.

Affected products

Chan Fatfs — versions 0
Elm-chan Fatfs

Weakness classification (CWE)

CWE-120 — Buffer Copy without Checking Size of Input (Classic Buffer Overflow)

References

44488dab-36db-4358-99f9-bc116477f914 (Exploit, Third Party Advisory, third-party-advisory)
44488dab-36db-4358-99f9-bc116477f914 (Exploit, technical-description, Third Party Advisory)
44488dab-36db-4358-99f9-bc116477f914 (Product, product)
44488dab-36db-4358-99f9-bc116477f914 (Third Party Advisory, third-party-advisory)

Frequently asked questions

What is CVE-2026-6688?: CVE-2026-6688 is a high-severity vulnerability in Chan Fatfs, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 7.6/10. Published 2026-07-01.
How severe is CVE-2026-6688?: High severity. CVSS v3 base score is 7.6 out of 10.