CVE-2026-6683 in FatFs
Summary
by MITRE • 07/01/2026
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.
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Analysis
by VulDB Data Team • 07/01/2026
The vulnerability exists within FatFs version R0.16 and earlier implementations where a divide-by-zero error occurs during exFAT filesystem synchronization operations. This flaw specifically manifests when crafted metadata causes the calculation n_fatent - 2 to evaluate to zero, creating a mathematical division by zero condition that crashes the filesystem driver. The issue maps directly to CWE-369 which categorizes divide-by-zero conditions as a fundamental programming error that can lead to denial of service and system instability. This vulnerability resides in the exFAT filesystem implementation's sync logic where the software attempts to perform arithmetic operations without proper validation of divisor values.
The technical exploitation occurs when maliciously crafted metadata is processed during write or sync operations within the exFAT filesystem driver. When the n_fatent variable contains a value that makes n_fatent - 2 equal to zero, subsequent calculations that depend on this value trigger the divide-by-zero exception. This condition typically happens in scenarios where filesystem metadata has been manipulated to create invalid cluster chain structures or when processing corrupted or specially crafted filesystem images. The vulnerability affects systems using FatFs implementations for exFAT filesystem support, particularly those handling external storage devices or network-delivered update media.
Operational impact of this vulnerability includes potential system crashes and denial of service conditions that can render affected systems unusable until the filesystem is properly unmounted and remounted. While the CVSS score indicates a medium severity rating with vector CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H, the actual impact depends on the execution environment and whether the system has sufficient protections against malicious filesystem content. The estimated CISA SSVC vectors indicate exploitation at Proof of Concept level with partial technical impact, suggesting that while the vulnerability is not easily exploitable in the wild, it can be leveraged by attackers who have access to update media or can influence filesystem content.
Mitigation strategies include immediate upgrade to FatFs version R0.17 or later where this specific divide-by-zero condition has been addressed through proper input validation and boundary checking. System administrators should implement strict validation of external storage devices and update media before processing, particularly in environments where untrusted content might be introduced. The fix typically involves adding conditional checks to verify that the divisor value is non-zero before performing division operations, aligning with standard secure coding practices recommended by both CWE guidelines and industry security frameworks such as those outlined in the ATT&CK framework for operating system exploitation techniques. Organizations should also consider implementing filesystem monitoring solutions to detect anomalous cluster chain structures that might indicate attempts to trigger this vulnerability.