CVE-2025-38663 in Linux
Summary
by MITRE • 08/22/2025
In the Linux kernel, the following vulnerability has been resolved:
nilfs2: reject invalid file types when reading inodes
To prevent inodes with invalid file types from tripping through the vfs and causing malfunctions or assertion failures, add a missing sanity check when reading an inode from a block device. If the file type is not valid, treat it as a filesystem error.
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Analysis
by VulDB Data Team • 05/29/2026
The vulnerability identified as CVE-2025-38663 affects the Linux kernel's nilfs2 filesystem implementation and represents a critical security flaw that could lead to system instability and potential exploitation. This issue resides within the virtual filesystem layer where inode data is processed and validated during filesystem operations. The nilfs2 filesystem, which stands for New Implementation of Log-Structured File System version 2, is designed for high-performance logging and recovery capabilities but suffers from insufficient input validation during inode reading operations. The vulnerability specifically targets the kernel's handling of inode metadata when reading from block devices, creating a potential pathway for malformed data to bypass normal validation checks and propagate through the system's virtual filesystem layer.
The technical flaw manifests as a missing sanity check that should validate file type identifiers when reading inode structures from storage devices. In normal operation, the kernel should verify that inode file types conform to expected values before processing them further through the virtual filesystem interface. However, this validation step is absent, allowing invalid file type values to pass through unchecked. When an inode with an invalid file type is encountered, the system's assertion mechanisms may fail, leading to kernel panics or other forms of system instability. The vulnerability's classification as a filesystem error indicates that the kernel properly identifies the malformed data but lacks appropriate handling procedures to prevent cascading failures throughout the system's memory management and filesystem operations subsystems.
The operational impact of this vulnerability extends beyond simple system crashes to potentially enable more sophisticated attack vectors. An attacker who can manipulate filesystem data or gain write access to a nilfs2 filesystem could craft malicious inodes with invalid file types to trigger assertion failures, causing denial of service conditions that could disrupt critical system operations. The vulnerability's presence in the kernel's core filesystem handling code means that any process accessing files on a nilfs2 filesystem could potentially trigger the flaw, making it particularly dangerous in multi-user or networked environments. The lack of proper error handling for invalid file types creates opportunities for exploitation that could lead to privilege escalation or information disclosure, as the kernel's response to malformed data could reveal internal system state or create conditions for further attacks.
Mitigation strategies for CVE-2025-38663 should focus on implementing the missing validation logic that was added to the kernel's nilfs2 implementation. System administrators should prioritize updating to kernel versions that include the fix, which typically involves adding explicit checks for valid file type values during inode reading operations. The fix aligns with common security practices for preventing malformed input processing and follows established principles for robust filesystem error handling. Organizations should also implement monitoring for system instability or assertion failures that might indicate exploitation attempts. This vulnerability demonstrates the importance of input validation in kernel code and reinforces the need for comprehensive testing of filesystem implementations against malformed data conditions. The fix addresses a CWE-129 weakness related to insufficient validation of input data, and may also contribute to preventing techniques described in the ATT&CK framework under filesystem manipulation and privilege escalation tactics. Regular security audits of filesystem implementations and kernel modules should be conducted to identify similar validation gaps that could create similar vulnerabilities in other system components.