CVE-2026-6686 - Vulnerability Details - OpenCVE

FatFs R0.16 and earlier contains an uninitialized cluster exposure when f_lseek() extends files beyond EOF without zero-filling newly allocated clusters. This maps to CWE-908 (Use of Uninitialized Resource). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (4.6, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Partial.

No CVSS v4.0

Attack Vector Physical

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact High

Integrity Impact None

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploitation poc

Automatable no

Technical Impact partial

Vendors	Products
Chan	Fatfs

No data.

No data.

References

Link	Providers
https://elm-chan.org/fsw/ff/
https://github.com/runZeroInc/vulns-2026-fatfs-chance
https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/
https://www.runzero.com/blog/fatfs-bugs/

History

Mon, 06 Jul 2026 23:15:00 +0000

Type	Values Removed	Values Added
First Time appeared		Chan Chan fatfs
Vendors & Products		Chan Chan fatfs

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 contains an uninitialized cluster exposure when f_lseek() extends files beyond EOF without zero-filling newly allocated clusters. This maps to CWE-908 (Use of Uninitialized Resource). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (4.6, Medium). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Partial.
Title		FatFs Use of Uninitialized Clusters After Seek Past EOF
Weaknesses		CWE-908
References		https://elm-chan.org/fsw/ff/ https://github.com/runZeroInc/vulns-2026-fatfs-chance https://www.runzero.com/advisories/fatfs-uninit-cluster-exposure-cve-2026-6686/ https://www.runzero.com/blog/fatfs-bugs/
Metrics		cvssV3_1 `{'score': 4.6, 'vector': 'CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N'}`

MITRE

Status: PUBLISHED

Assigner: runZero

Published: 2026-07-01T13:55:09.072Z

Updated: 2026-07-01T15:05:27.926Z

Reserved: 2026-04-20T15:06:22.242Z

Link: CVE-2026-6686

Vulnrichment

Updated: 2026-07-01T15:05:15.476Z

NVD

No data.

Redhat

No data.

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