CVE-2026-6688
FatFs Buffer Overflow via Unbounded LFN Filename Copy
- State
- Published
- Severity
- 7.6 High
- Published
- Jul 1, 2026
- Updated
- Jul 1, 2026
- Reserved
- Apr 20, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 7.6 High | CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H | runZero |
Weaknesses
- CWE-120 Buffer Copy without Checking Size of Input
Affected Products
| Product | Versions |
|---|---|
FatFsChaN |
|
References
- https://www.runzero.com/blog/fatfs-bugs/third-party-advisory
- https://github.com/runZeroInc/vulns-2026-fatfs-chancetechnical-description
- https://elm-chan.org/fsw/ff/product
- https://www.runzero.com/advisories/fatfs-long-fn-of-downstream-cve-2026-6688/third-party-advisory
Every record here comes from the CVE Program’s CVE List. © 1999–2026 The MITRE Corporation. CVE is a registered trademark of The MITRE Corporation. The records are reproduced under the CVE Program terms of use.