Vulnerability · Published Jul 1, 2026 · Assigned by runZero

CVE-2026-6683FatFs Divide-by-Zero in exFAT Sync

Medium 4.6

In plain English

A medium-severity security flaw in FatFs from ChaN. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 23% of all known vulnerabilities).

Severity (CVSS 3.1)4.6Medium

Exploit odds (30 days)0.3%top 76.5% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

FatFs R0.16 and earlier contains a divide-by-zero in exFAT sync logic bug when crafted metadata causes n_fatent - 2 to be zero during write/sync operations. This maps to CWE-369 (Divide By Zero). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (4.6, Medium). Network-delivered update media can make this remote in some pipelines. The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Partial.

Affected products (as reported)

Vendor	Product	Versions
ChaN	FatFs	0 – through R0.16

Weakness: CWE-369 · Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://www.runzero.com/blog/fatfs-bugs/ third-party-advisory
https://github.com/runZeroInc/vulns-2026-fatfs-chance technical-description
https://elm-chan.org/fsw/ff/ product
https://www.runzero.com/advisories/fatfs-exfat-divide-by-zero-cve-2026-6683 third-party-advisory