CVE-2026-6686 | FatFs R0.16 and earlier contains an uninitialized cluster ex… | CVSS 4.6 MEDIUM

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.

Metadata

CVE ID: CVE-2026-6686
State: PUBLISHED
Assigner: runZero
Reserved: 2026-04-20 15:06 UTC
Published: 2026-07-01 13:55 UTC
Last updated: 2026-07-01 15:05 UTC
Primary CWE: CWE-908
CWE-908 Use of uninitialized resource
Vendor / Product: ChaN / FatFs
Sources: cve.org · NVD

Severity & Metrics

4.6 MEDIUM CVSS 3.1

CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

SSVC — CISA Coordinator

Exploitation: PoC
Automatable: no
Tech. Impact: partial

Affected products (1)

Vendor	Product	Platform	Versions
ChaN	FatFs	—	0 ≤ R0.16

Weakness (CWE)

CWE	Source	Description
CWE-908	cna	CWE-908 Use of uninitialized resource

CVSS scores (1)

Score	Severity	Version	Source	Vector
4.6	MEDIUM	3.1	cna	CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

References (4)