CVE-2026-6687 in FatFs
Summary
by MITRE • 07/01/2026
FatFs R0.16 and earlier contains a stack overflow bug in f_getlabel() because exFAT label length (XDIR_NumLabel) is trusted without enforcing spec maximums. This maps to CWE-121 (Stack-based Buffer Overflow). 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). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total.
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Analysis
by VulDB Data Team • 07/01/2026
The FatFs file system library version 0.16 and earlier contains a critical stack-based buffer overflow vulnerability in the f_getlabel() function that arises from improper validation of exFAT label length parameters. This vulnerability represents a classic stack overflow condition where the XDIR_NumLabel field from exFAT directory entries is trusted without enforcing proper maximum limits defined by the file system specification. The flaw occurs when the library processes exFAT volume labels without validating that the label length conforms to established bounds, allowing maliciously crafted file system structures to overwrite adjacent stack memory.
The technical implementation of this vulnerability stems from the library's failure to enforce specification-compliant maximums for label lengths in exFAT format directory entries. When processing volume labels, FatFs directly uses the XDIR_NumLabel value without validating it against the maximum allowed length as defined by the exFAT specification, creating an opportunity for attackers to craft file system structures with excessively long label fields that exceed the allocated buffer space on the stack.
This vulnerability maps directly to CWE-121, which specifically addresses stack-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The impact of this flaw extends beyond simple memory corruption as it can lead to arbitrary code execution when the stack overflow results in control flow redirection or when the overflow corrupts critical program state information.
The operational impact of this vulnerability is severe given that FatFs is widely deployed across embedded systems, IoT devices, and various storage applications. The CVSS v3.1 score of 7.6 indicates a high severity threat with attack vector requiring physical access but no user interaction, while the CISA SSVC assessment showing Proof of Concept exploitation and total technical impact underscores the practical danger this presents to deployed systems. Attackers can potentially leverage this vulnerability to execute arbitrary code on affected devices, making it particularly dangerous in embedded environments where system compromise can lead to complete device control.
Mitigation strategies should focus on immediate patching of FatFs library versions to 0.17 or later where the stack overflow has been addressed through proper input validation and enforcement of maximum label length limits. Organizations should also implement runtime monitoring for unusual file system access patterns and consider deploying defensive measures such as stack canaries or address space layout randomization to reduce exploitability. Additionally, system administrators should conduct thorough inventory assessments to identify all devices using vulnerable FatFs versions and ensure proper firmware updates are applied across the entire deployment landscape.
The vulnerability demonstrates the importance of strict adherence to file system specifications and proper bounds checking in storage system implementations, particularly when dealing with variable-length fields that can be manipulated by external inputs. This flaw serves as a reminder that even well-established libraries require continuous security assessment and validation to prevent critical vulnerabilities from persisting across multiple versions and deployments.