CVE-2024-53690 is a vulnerability identified in the Linux kernel's NILFS2 (New Implementation of a Log-structured File System) implementation. The issue arises from improper handling of deleted inodes during directory removal operations. Specifically, the inode bitmap corruption leads to an inode number, which should correspond to a deleted ".nilfs" file, being reassigned erroneously by the nilfs_mkdir function to a new directory entry "file0". This results in inode duplication within the same task context when unmounting and removing directories ".nilfs" and "file0". The duplication causes an underflow of the i_nlink field during rmdir operations, which is a critical reference count for inode link tracking. The kernel triggers a warning in nilfs_rmdir due to this inconsistent state. The vulnerability is rooted in the failure to check the i_nlink value in nilfs_iget(), which should indicate if an inode has been deleted (i_nlink == 0). Without this check, the inode is reused improperly, leading to potential filesystem inconsistencies and instability. The patch approach involves verifying the i_nlink count and reclaiming the inode via iput if it is zero, preventing reuse of deleted inodes. This vulnerability was discovered and reported by syzbot, a kernel fuzzing infrastructure, and affects specific Linux kernel versions identified by commit hashes. No known exploits in the wild have been reported as of the publication date (January 11, 2025). No CVSS score has been assigned yet.

For European organizations, the impact of CVE-2024-53690 can be significant, particularly for those relying on Linux systems with NILFS2 file systems, which are used in some specialized storage and embedded environments. The vulnerability can lead to filesystem corruption, data integrity issues, and potential denial of service (DoS) conditions due to kernel warnings and possible crashes triggered by inode duplication and reference count underflows. This can disrupt critical services, especially in sectors such as finance, telecommunications, and manufacturing where Linux servers are prevalent. Although no direct remote code execution or privilege escalation is indicated, the instability caused by corrupted filesystem metadata can lead to system outages and data loss, impacting availability and integrity. European organizations with high availability requirements or those operating critical infrastructure should be particularly cautious. The lack of known exploits reduces immediate risk, but the vulnerability's presence in kernel code means that attackers with local access or the ability to manipulate filesystem operations could potentially trigger the issue.

1. Immediate application of the official Linux kernel patches that address the inode reuse and i_nlink underflow issue is critical. Monitor Linux kernel mailing lists and distribution security advisories for updated kernel releases containing the fix. 2. For organizations using NILFS2, consider auditing and limiting the use of this filesystem if not strictly necessary, or migrating critical data to more widely used and actively maintained filesystems like ext4 or XFS until the patch is applied. 3. Implement strict access controls to limit local user permissions, reducing the risk of exploitation by unprivileged users who might trigger the inode duplication condition. 4. Enhance monitoring of kernel logs for warnings related to nilfs_rmdir or inode reference count anomalies to detect attempts to exploit or trigger the vulnerability. 5. Conduct filesystem integrity checks and backups regularly to mitigate potential data corruption impacts. 6. For embedded or specialized Linux systems where kernel updates may be delayed, consider deploying kernel live patching solutions or isolating affected systems to minimize exposure.