Unbounded Loop Vulnerability in FatFs by Elm-Chan
CVE-2026-6684

4.6MEDIUM

Key Information:

Vendor

Chan

Status
Fatfs
Vendor
CVE Published:
1 July 2026

What is CVE-2026-6684?

An unbounded loop vulnerability exists in FatFs versions prior to R0.16 when performing GPT scanning with 'FF_LBA64 = 1'. This vulnerability is triggered by an excessive loop count derived from the GPT header field GPTH_PtNum. This can cause lengthy or infinite mount-time scans, disrupting system performance and potentially leading to denial-of-service conditions. It is crucial for users to update to the latest version of FatFs to mitigate this risk.

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.
.