CVE-2026-6685

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.

CVSS v3 6.1 MEDIUM

6.1^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 0.9 / Impact : 5.2

Attack Vector PHYSICAL

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://elm-chan.org/fsw/ff/	Product
https://github.com/runZeroInc/vulns-2026-fatfs-chance	Third Party Advisory Exploit
https://www.runzero.com/advisories/fatfs-unsigned-sub-wrap-cve-2026-6685/	Third Party Advisory
https://www.runzero.com/blog/fatfs-bugs/	Third Party Advisory Exploit
https://github.com/runZeroInc/vulns-2026-fatfs-chance	Third Party Advisory Exploit

Configurations

Configuration 1 (hide)

cpe:2.3:a:elm-chan:fatfs:*:*:*:*:*:*:*:*

History

02 Jul 2026, 14:38

Type	Values Removed	Values Added
CPE		cpe:2.3:a:elm-chan:fatfs::::::::
First Time		Elm-chan Elm-chan fatfs
References	~~() https://elm-chan.org/fsw/ff/ -~~	() https://elm-chan.org/fsw/ff/ - Product
References	~~() https://github.com/runZeroInc/vulns-2026-fatfs-chance -~~	() https://github.com/runZeroInc/vulns-2026-fatfs-chance - Third Party Advisory, Exploit
References	~~() https://www.runzero.com/advisories/fatfs-unsigned-sub-wrap-cve-2026-6685/ -~~	() https://www.runzero.com/advisories/fatfs-unsigned-sub-wrap-cve-2026-6685/ - Third Party Advisory
References	~~() https://www.runzero.com/blog/fatfs-bugs/ -~~	() https://www.runzero.com/blog/fatfs-bugs/ - Third Party Advisory, Exploit

01 Jul 2026, 17:16

Type	Values Removed	Values Added
References	~~() https://github.com/runZeroInc/vulns-2026-fatfs-chance -~~	() https://github.com/runZeroInc/vulns-2026-fatfs-chance -

01 Jul 2026, 15:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-07-01 15:17

Updated : 2026-07-02 14:38

NVD link : CVE-2026-6685

Mitre link : CVE-2026-6685

CVE.ORG link : CVE-2026-6685

JSON object : View

Products Affected

elm-chan

fatfs

CWE

CWE-191

Integer Underflow (Wrap or Wraparound)

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