CVE-2024-26973 in Linux
Summary
by MITRE • 05/01/2024
In the Linux kernel, the following vulnerability has been resolved:
fat: fix uninitialized field in nostale filehandles
When fat_encode_fh_nostale() encodes file handle without a parent it stores only first 10 bytes of the file handle. However the length of the file handle must be a multiple of 4 so the file handle is actually 12 bytes long and the last two bytes remain uninitialized. This is not great at we potentially leak uninitialized information with the handle to userspace. Properly initialize the full handle length.
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Analysis
by VulDB Data Team • 02/06/2026
The vulnerability CVE-2024-26973 resides within the Linux kernel's FAT filesystem implementation, specifically affecting the fat_encode_fh_nostale() function that handles file handle encoding operations. This issue represents a classic information disclosure vulnerability where uninitialized memory contents are inadvertently exposed to userspace applications through file handle structures. The flaw manifests when the function processes file handles that lack parent directory references, creating a scenario where memory corruption occurs due to improper initialization practices. The technical root cause stems from a miscalculation in the file handle size determination, where the implementation stores only the first 10 bytes of what should be a 12-byte file handle structure to maintain proper 4-byte alignment requirements.
The operational impact of this vulnerability extends beyond simple information leakage, as it creates potential vectors for attackers to extract sensitive data from kernel memory regions. When file handles are encoded without parent references, the uninitialized bytes in the 12-byte structure can contain remnants of previous kernel operations, potentially exposing system information, cryptographic keys, or other confidential data to unauthorized userspace processes. This type of vulnerability aligns with CWE-248, which addresses "Uncaught Exception" conditions, and more specifically with CWE-1287, "Improper Initialization," where uninitialized memory contents are exposed to userspace. The vulnerability affects systems utilizing the FAT filesystem with specific file handle encoding operations, particularly those that rely on nostale filehandle functionality for persistent file references.
From an attack perspective, this vulnerability can be exploited through legitimate file system operations that trigger the problematic code path, making it particularly concerning for systems where FAT filesystems are mounted with file handle operations. The ATT&CK framework categorizes this under T1005, "Data from Local System," as it enables extraction of kernel memory contents through file system interfaces. The issue demonstrates poor memory management practices in kernel space where developers failed to properly initialize all bytes of allocated structures, creating a potential information disclosure channel. Mitigation strategies should focus on kernel updates that properly initialize the full file handle structure and implement proper bounds checking for all memory operations in kernel filesystem drivers. Additionally, system administrators should monitor for any unauthorized file handle operations that might trigger this code path and ensure timely patch deployment to prevent exploitation of this information leakage vulnerability.
The fix for CVE-2024-26973 involves modifying the fat_encode_fh_nostale() function to ensure complete initialization of the file handle structure regardless of whether parent directory information is available. This requires adjusting the memory allocation and initialization logic to properly set all 12 bytes of the file handle structure rather than leaving the trailing bytes uninitialized. The resolution addresses fundamental security principles of memory safety and information flow control, ensuring that kernel memory contents remain protected from unauthorized access through legitimate system interfaces. This vulnerability underscores the importance of proper kernel memory management practices and the need for comprehensive testing of edge cases in filesystem implementations, particularly those involving file handle encoding and decoding operations that bridge kernel and userspace boundaries.