# CVE-2026-6682: ChaN FatFs integer overflow in mount_volume

Source: https://junglewise.ai/threats/cve-2026-6682-chan-fatfs-integer-overflow-in-mount-volume  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-01. Updated: 2026-07-01  
License: CC BY 4.0 with a link back

CVE-2026-6682 · Severity: high · CVSS 7.6 · Published 2026-07-01

FatFs is a widely used open-source software library that allows embedded devices, such as IoT sensors and industrial controllers, to read and write data on SD cards and USB drives. A vulnerability in how the library handles FAT32 file systems allows an attacker to provide a specially crafted storage device or update file that triggers memory corruption. This can lead to a complete system takeover, data theft, or permanent device failure, impacting a vast range of consumer and industrial electronics.

Technologies: [ChaN FatFs](https://junglewise.ai/threats/technologies/fatfs). Vendors: [ChaN](https://junglewise.ai/threats/vendors/chan).

## Quick answers

**Is CVE-2026-6682 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-6682 being exploited in the wild.

**How severe is CVE-2026-6682?** High severity, with a CVSS score of 7.6, published 1 July 2026.

**Which products and versions are affected?** ChaN FatFs R0.16 and earlier.

**Is there a fix for CVE-2026-6682?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-6682 attacked?** It is attacked with physical access or over the network, in a software library.

**Am I affected by CVE-2026-6682?** Check whether you run ChaN FatFs at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An integer overflow (CWE-190) exists in the mount_volume() function of FatFs when processing FAT32 volumes. Specifically, the multiplication of the FAT size (fasize) by the number of FATs (fs->n_fats) can wrap around on 32-bit systems if provided with crafted values in the BIOS Parameter Block (BPB). This overflow causes the library to miscalculate the location of the data area (fs->database), allowing an attacker to forge file metadata returned by functions like f_stat() and f_readdir(). Downstream applications that rely on the resulting finfo.fsize to allocate buffers or limit f_read() operations become vulnerable to heap or stack-based buffer overflows. While the primary attack vector is physical (malicious SD card), the vulnerability can also be triggered via network-delivered OTA update containers if they are mounted before full cryptographic verification.

## Affected products

- ChaN FatFs R0.16 and earlier

## Timeline

- 2026-06-30: advisory: Initial advisory published by runZero
- 2026-07-01: disclosed: CVE-2026-6682 published to NVD

## References

- [https://elm-chan.org/fsw/ff/](https://elm-chan.org/fsw/ff/)
- [https://github.com/runZeroInc/vulns-2026-fatfs-chance](https://github.com/runZeroInc/vulns-2026-fatfs-chance)
- [https://www.runzero.com/advisories/fatfs-fat32-int-of-mnt-cve-2026-6682/](https://www.runzero.com/advisories/fatfs-fat32-int-of-mnt-cve-2026-6682/)
- [https://www.runzero.com/blog/fatfs-bugs/](https://www.runzero.com/blog/fatfs-bugs/)

## Related threats

- [ChaN FatFs buffer overflow in long filename handling](https://junglewise.ai/threats/cve-2026-6688-chan-fatfs-buffer-overflow-in-long-filename-handling)
- [ChaN FatFs stack overflow in f_getlabel](https://junglewise.ai/threats/cve-2026-6687-chan-fatfs-stack-overflow-in-f-getlabel)
- [ChaN FatFs uninitialized cluster exposure in f_lseek](https://junglewise.ai/threats/cve-2026-6686-chan-fatfs-uninitialized-cluster-exposure-in-f-lseek)
- [ChaN FatFs integer underflow in f_read and f_write](https://junglewise.ai/threats/cve-2026-6685-chan-fatfs-integer-underflow-in-f-read-and-f-write)
- [ChaN FatFs infinite loop in GPT partition scanning](https://junglewise.ai/threats/cve-2026-6684-chan-fatfs-infinite-loop-in-gpt-partition-scanning)