Vulnerability · Published Jul 1, 2026 · Assigned by runZero

CVE-2026-6682FatFs Integer Overflow in FAT32 Volume Mount

High 7.6

In plain English

A high-severity integer overflow in FatFs from ChaN. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 25% of all known vulnerabilities).

Severity (CVSS 3.1)7.6High

Exploit odds (30 days)0.3%top 74.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

In FatFS R0.16 and earlier contains a FAT32 integer overflow bug in mount_volume() where fasize *= fs->n_fats can wrap, leading to attacker-controlled file-size metadata and unsafe read lengths in downstream callers. This maps to CWE-190 (Integer Overflow or Wraparound). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H (7.6, High). Remote delivery is also possible in OTA/update pipelines. The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total.

Affected products (as reported)

Vendor	Product	Versions
ChaN	FatFs	0 – through R0.16

Weakness: CWE-190 · Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/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-fat32-int-of-mnt-cve-2026-6682/ third-party-advisory