CVE-2026-89829 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix to pass folio->index to f2fs_sanity_check_node_footer()
Otherwise in f2fs_sanity_check_node_footer(), it will check the same nid incorrectly.
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Analysis
by VulDB Data Team • 09/16/2026
The F2FS file system, developed by Samsung for flash storage devices such as SSDs and eMMC, relies on a complex node structure to manage metadata like inode tables, directory entries, and data block mappings. A critical logical flaw was identified within the sanity check mechanism used during node footer validation, specifically in the function f2fs_sanity_check_node_footer(). This vulnerability stems from an incorrect parameter passing issue where the folio index is not properly utilized for identifying the specific node being validated. In Linux kernel memory management, a folio represents a contiguous set of pages, and its index serves as a unique identifier within that context. When this index is omitted or incorrectly handled during the sanity check process, the validation logic fails to distinguish between different nodes effectively.
The technical consequence of this oversight is that f2fs_sanity_check_node_footer() may validate the same node identification number multiple times instead of checking distinct nodes as intended. This redundancy in verification means that other potentially corrupted or malformed nodes are left unchecked during critical file system operations such as mounting, checkpointing, or garbage collection. The integrity checks designed to prevent data corruption and maintain consistency across the flash storage medium become ineffective for a significant portion of the metadata structure. Without proper differentiation based on the folio index, the kernel cannot reliably detect structural inconsistencies that could lead to silent data loss or file system instability.
From an operational perspective, this vulnerability poses a risk to data integrity and system stability, particularly in environments where F2FS is used for high-write workloads typical of mobile devices and embedded systems. If corrupted node footers are not detected due to the flawed sanity check logic, subsequent operations may proceed with invalid metadata pointers. This can lead to unexpected behavior such as file access errors, directory listing failures, or even kernel panics if the corruption affects critical system structures. The lack of proper validation allows minor inconsistencies to propagate through the file system tree, potentially escalating into severe data loss scenarios that are difficult to recover from without a full backup restoration.
This issue aligns with CWE-20 Improper Input Validation and CWE-754 Incorrect Check for Unusual or Exceptional Conditions, as the code fails to correctly validate the structural integrity of node footers due to improper identification logic. In terms of attack vectors, while this is primarily a reliability and stability issue rather than a direct exploitation vector for privilege escalation, it falls under ATT&CK technique T1485 Data Destruction if an attacker can induce conditions that trigger the flawed validation path on corrupted data. The vulnerability highlights the importance of rigorous parameter handling in low-level kernel subsystems where memory layout and object identification are critical to security.
Mitigation strategies involve applying the upstream Linux kernel patch that corrects the function call by ensuring folio->index is passed correctly to f2fs_sanity_check_node_footer(). System administrators should ensure their kernels are updated to versions containing this fix, particularly those targeting embedded devices or servers using F2FS for flash storage. Regular file system checks and monitoring of kernel logs for I/O errors can help detect early signs of metadata corruption that might have been missed due to this vulnerability. Maintaining up-to-date security patches is essential as the Linux kernel community actively addresses such logical flaws to preserve the robustness of modern file systems against data integrity threats.