TI-2026-05863 Aliases CVE-2026-6683 GHSA-74cg-p8q3-4c3q

FatFs Divide-by-Zero in exFAT Sync

LOW 21CWE-369Published 2026-07-01 · Updated 2026-07-01

Key facts

Attack vector: Physical
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: Denial of service
Confidentiality · integrity · availability: None · None · High
Fix status: No fix listed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-369.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00306 23rd percentileScored 2026-11-07

Public exploit Yes 2 exploit referencesTagged by NVD

Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
ChaN	FatFs	up to R0.16	—	No fix listed	CNA

FatFs VendorChaN Affected up to R0.16 Fixed in — No fix listed CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:elm-chan:fatfs::::::::	up to r0.16	Vulnerable	ChaN

cpe:2.3:a:elm-chan:fatfs:*:*:*:*:*:*:*:* Versions up to r0.16 Vulnerable ·ChaN

Remediation

No fixed version listed by the sources yet.

Timeline

2026-10-02 Threatist record created from CVE-2026-6683
2026-10-03 Alias added: GHSA-74cg-p8q3-4c3q

References

Exploit 2

Advisory 1

https://www.runzero.com/advisories/fatfs-exfat-divide-by-zero-cve-2026-6683

Other 1

https://elm-chan.org/fsw/ff/

TI-2026-05867 FatFs Buffer Overflow via Unbounded LFN Filename Copy CVSS 3.1HIGH 7.6
TI-2026-05866 FatFs Stack Buffer Overflow via Uncapped exFAT Label Length CVSS 3.1HIGH 7.6
TI-2026-05862 FatFs Integer Overflow in FAT32 Volume Mount CVSS 3.1HIGH 7.6
TI-2026-05865 FatFs Use of Uninitialized Clusters After Seek Past EOF CVSS 3.1MEDIUM 4.6
TI-2026-05864 FatFs Infinite Loop in GPT Partition Scan CVSS 3.1MEDIUM 4.6

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences