FatFs Buffer Overflow via Unbounded LFN Filename Copy
Summary
| CVE | CVE-2026-6688 |
|---|---|
| State | PUBLISHED |
| Assigner | runZero |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-07-01 15:17:13 UTC |
| Updated | 2026-07-01 18:31:17 UTC |
| 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. |
Risk And Classification
Primary CVSS: v3.1 7.6 HIGH from 44488dab-36db-4358-99f9-bc116477f914
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Problem Types: CWE-120 | CWE-120 CWE-120 Buffer Copy without Checking Size of Input
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | 44488dab-36db-4358-99f9-bc116477f914 | Secondary | 7.6 | HIGH | CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H |
| 3.1 | CNA | CVSS | 7.6 | HIGH | CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H |
CVSS v3.1 Breakdown
Attack Vector
PhysicalAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
ChangedConfidentiality
HighIntegrity
HighAvailability
HighCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Vendor Declared Affected Products
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| www.runzero.com/blog/fatfs-bugs | 44488dab-36db-4358-99f9-bc116477f914 | www.runzero.com | |
| www.runzero.com/advisories/fatfs-long-fn-of-downstream-cve-2026-6688 | 44488dab-36db-4358-99f9-bc116477f914 | www.runzero.com | |
| github.com/runZeroInc/vulns-2026-fatfs-chance | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | github.com | |
| elm-chan.org/fsw/ff | 44488dab-36db-4358-99f9-bc116477f914 | elm-chan.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: HD Moore of runZero, Inc. (en)
CNA: Tod Beardsley of runZero, Inc. (en)
There are currently no legacy QID mappings associated with this CVE.