exFAT Logic Bug in FatFs R0.16 and Earlier by Chan
CVE-2026-6683

4.6MEDIUM

Key Information:

Vendor

Chan

Status
Fatfs
Vendor
CVE Published:
1 July 2026

What is CVE-2026-6683?

A divide-by-zero error exists in the exFAT sync logic of FatFs versions R0.16 and earlier, triggered by crafted metadata that results in n_fatent being zero during write or sync operations. This vulnerability falls under the category of CWE-369 and allows potential impact during data synchronization processes. Moreover, this issue may facilitate remote exploitation when updates are delivered through network pipelines. Users and administrators are advised to assess their systems for affected versions and apply mitigations where possible.

Affected Version(s)

FatFs 0

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

CVSS V3.1

Score:
4.6
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Physical
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

HD Moore of runZero, Inc.
Tod Beardsley of runZero, Inc.
.