CVE-2026-6686: 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

mediumCVSS 4.6CVE-2026-6686

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.

Details

Source: NVD Recent CVEs (US · database · site)
Severity: medium — CVSS 4.6
Published: 2026-07-01
Last updated: 2026-07-02
Exploitation: Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-6686

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-66860.18% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 7% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-6686	coverage & exploitation status	NVD · CVE.org

Recent advisories for FatFs R0.16 and

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

highCVE-2026-6688: FatFs R0.16 and earlier contains a downstream-caller vulnerability pattern associated with FatF…nvd · 2026-07-01
highCVE-2026-6687: FatFs R0.16 and earlier contains a stack overflow bug in f_getlabel() because exFAT label lengt…nvd · 2026-07-01
mediumCVE-2026-6685: FatFs R0.16 and earlier exhibits a stale dirty-cache skip via unsigned-subtraction wrap in f_re…nvd · 2026-07-01
mediumCVE-2026-6684: FatFs prior to R0.16 that use GPT scanning with 'FF_LBA64 = 1' contains an issue where an unbou…nvd · 2026-07-01
mediumCVE-2026-6683: FatFs R0.16 and earlier contains a divide-by-zero in exFAT sync logic bug when crafted metadata…nvd · 2026-07-01
highCVE-2026-6682: In FatFS R0.16 and earlier contains a FAT32 integer overflow bug in mount_volume() where fasize…nvd · 2026-07-01

CVE-2026-6686: 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

Details

Exploitation outlook

Referenced CVEs

Recent advisories for FatFs R0.16 and

More from NVD Recent CVEs