FatFs Integer Underflow in Dirty-Sector Cache Flush
Summary
| CVE | CVE-2026-6685 |
|---|---|
| State | PUBLISHED |
| Assigner | runZero |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-07-01 15:17:12 UTC |
| Updated | 2026-07-01 18:31:17 UTC |
| Description | FatFs R0.16 and earlier exhibits a stale dirty-cache skip via unsigned-subtraction wrap in f_read() / f_write() (fp->sect - sect < cc) during interleaved read/write on fragmented filesystems. This maps to CWE-191 (Integer Underflow). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H (6.1, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total. |
Risk And Classification
Primary CVSS: v3.1 6.1 MEDIUM from 44488dab-36db-4358-99f9-bc116477f914
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Problem Types: CWE-191 | CWE-191 CWE-191 Integer underflow (wrap or wraparound)
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | 44488dab-36db-4358-99f9-bc116477f914 | Secondary | 6.1 | MEDIUM | CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H |
| 3.1 | CNA | CVSS | 6.1 | MEDIUM | CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H |
CVSS v3.1 Breakdown
Attack Vector
PhysicalAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
HighAvailability
HighCVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/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 | |
| github.com/runZeroInc/vulns-2026-fatfs-chance | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | github.com | |
| www.runzero.com/advisories/fatfs-unsigned-sub-wrap-cve-2026-6685 | 44488dab-36db-4358-99f9-bc116477f914 | www.runzero.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.