Integer Overflow in FatFS Leading to Arbitrary Code Execution

Executive Summary

CVE-2026-6682 is a high-severity vulnerability in ChaN's FatFs R0.16 and earlier versions involving an integer overflow bug in the FAT32 file system implementation.

Specifically, in the mount_volume() function, the multiplication of the variable fasize by fs->n_fats can overflow due to 32-bit arithmetic limits, causing the value to wrap around.

This overflow allows an attacker to control file-size metadata, which can then be used to forge values in downstream functions like f_stat() and f_readdir().

By exploiting this, an attacker can cause memory corruption during file read operations such as f_read(), potentially leading to unsafe behavior.

The vulnerability is mapped to CWE-190 (Integer Overflow or Wraparound) and has a CVSS v3.1 score of 7.6 (High).

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Detection Guidance

Detection of CVE-2026-6682 involves identifying the presence of vulnerable versions of ChaN's FatFs R0.16 or earlier in your system or devices.

Since the vulnerability is related to the FAT32 integer overflow in the mount_volume() function, detection can focus on scanning for the FatFs library version and monitoring for suspicious file-size metadata manipulations.

Commands to detect the vulnerable FatFs version or suspicious activity are not explicitly provided in the available resources.

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Impact Analysis

This vulnerability can allow an attacker to manipulate file-size metadata in the FAT32 file system, leading to unsafe read lengths and memory corruption during file operations.

Such manipulation can cause crashes, data corruption, or potentially enable further exploitation depending on the context in which FatFs is used.

Remote exploitation is possible, especially in over-the-air (OTA) update pipelines, meaning attackers can deliver malicious FAT images remotely.

The flaw affects multiple downstream projects and embedded systems, increasing the risk in IoT devices and other systems relying on FatFs.

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Compliance Impact

The vulnerability in FatFs R0.16 and earlier allows attacker-controlled file-size metadata and unsafe read lengths, leading to potential memory corruption and data integrity issues.

Such impacts on data integrity and confidentiality could pose significant risks for compliance with standards and regulations like GDPR and HIPAA, which require protection of sensitive data and prevention of unauthorized data manipulation.

Specifically, the ability for an attacker to remotely exploit this vulnerability (e.g., via OTA/update pipelines) and manipulate file metadata could lead to unauthorized data access or corruption, undermining the confidentiality, integrity, and availability requirements mandated by these regulations.

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Mitigation Strategies

Immediate mitigation steps include avoiding the use of vulnerable FatFs R0.16 or earlier versions in your systems.

Since remote exploitation is possible via OTA/update pipelines, ensure that any FAT images or updates are verified and come from trusted sources.

If possible, restrict or monitor access to removable media or update mechanisms that could deliver crafted FAT images.

No official patch or vendor response was available as of the disclosure date, so consider applying custom checks or workarounds to validate file-size metadata before processing.

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