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.

No CVSS v4.0

Attack Vector Physical

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact High

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Exploitation poc

Automatable no

Technical Impact partial

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
ChaN FatFs unaffected
Version Status Constraints
0 affected ≤ R0.16

No data.

No data.

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Project Subscriptions

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Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://elm-chan.org/fsw/ff/ cve-icon
https://github.com/runZeroInc/vulns-2026-fatfs-chance cve-icon cve-icon
https://www.runzero.com/advisories/fatfs-unsigned-sub-wrap-cve-2026-6685/ cve-icon
https://www.runzero.com/blog/fatfs-bugs/ cve-icon
History

Wed, 01 Jul 2026 16:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Wed, 01 Jul 2026 14:30:00 +0000

Type Values Removed Values Added
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.
Title FatFs Integer Underflow in Dirty-Sector Cache Flush
Weaknesses CWE-191
References
Metrics cvssV3_1

{'score': 6.1, 'vector': 'CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H'}

Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: runZero

Published:

Updated: 2026-07-01T15:26:37.612Z

Reserved: 2026-04-20T15:06:21.250Z

Link: CVE-2026-6685

cve-icon Vulnrichment

Updated: 2026-07-01T15:26:33.909Z

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-07-01T16:45:04Z

Weaknesses