CVE-2026-98168 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix reparse buffer bounds in cifs_query_reparse_point()
In cifs_query_reparse_point(), the start >= end check before casting to struct reparse_data_buffer * only ensures the start pointer is within the response. It fails to verify that there is enough space remaining for the fixed 8-byte header of the structure.
If a server provides a DataOffset that leaves less than 8 bytes remaining, the check passes, but subsequent reads of ReparseTag and ReparseDataLength will occur out-of-bounds.
Fix this by ensuring the remaining space is at least the size of the reparse_data_buffer structure before accessing its fields.
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Analysis
by VulDB Data Team • 10/07/2026
The Common Vulnerabilities and Exposures identifier CVE-2024-10857 highlights a critical memory safety flaw within the Server Message Block client implementation of the Linux kernel, specifically affecting the cifs_query_reparse_point function. This vulnerability stems from an insufficient boundary check during the parsing of reparse point data structures returned by SMB servers. The core issue lies in how the code validates pointer arithmetic before casting raw response bytes into a structured C type known as struct reparse_data_buffer. While the existing logic verifies that the start pointer is not greater than or equal to the end pointer, this check only guarantees that the starting address falls within the allocated buffer boundaries. It completely fails to account for the size of the data structure being accessed, leaving a gap in validation where the remaining bytes might be fewer than required by the target struct definition.
From a technical perspective, the vulnerability is triggered when an SMB server provides a DataOffset value that points to a location within the response buffer such that less than eight bytes remain until the end of the allocated memory region. The reparse_data_buffer structure requires at least these initial bytes to safely read its header fields, specifically ReparseTag and ReparseDataLength. Because the original code did not verify that the remaining space was sufficient for this fixed-size header, it proceeded with a cast operation despite the inadequate buffer tailroom. This results in out-of-bounds memory reads when the kernel attempts to dereference these structure members. Such access patterns violate fundamental memory safety principles and can lead to unpredictable behavior depending on what data resides immediately after the allocated buffer in physical or virtual memory.
The operational impact of this flaw is significant, particularly given that SMB clients frequently interact with untrusted network servers. An attacker controlling a malicious SMB server could craft a specially crafted response containing an invalid DataOffset value designed to exploit this boundary condition. By doing so, they can force the kernel to read sensitive information from adjacent memory locations outside the intended buffer scope. This constitutes an out-of-bounds read vulnerability which may lead to information disclosure, allowing the attacker to leak kernel memory contents that could include cryptographic keys, process identifiers, or other confidential data. In more severe scenarios involving specific memory layouts and subsequent operations on corrupted pointers derived from these reads, the risk escalates toward potential denial of service conditions through kernel panics or crashes due to accessing unmapped pages.
This vulnerability aligns with CWE-125, which describes out-of-bounds read errors where software accesses memory beyond the end of a buffer. It also maps closely to MITRE ATT&CK technique T1083, specifically the file and directory discovery subtechnique, as SMB reparse points are often used in reconnaissance activities within Windows environments that Linux systems frequently mount or interact with. The failure to validate structural integrity against available space represents a classic example of improper input validation where assumptions about buffer sizes are not rigorously enforced during parsing operations.
To mitigate this risk, the primary remediation involves applying the kernel patch that corrects the bounds checking logic in cifs_query_reparse_point(). This fix ensures that before any casting or field access occurs, the code explicitly verifies that the remaining space from the start pointer to the end of the buffer is at least equal to the size of the reparse_data_buffer structure. System administrators should prioritize updating their Linux kernels to versions where this patch has been integrated and released as a security update. Additionally, organizations relying on SMB clients for file sharing operations should ensure that network segmentation policies restrict direct access from untrusted networks to internal systems running vulnerable kernel versions until patches are deployed. Regular auditing of SMB configurations and monitoring for anomalous connection patterns can further reduce the attack surface associated with this class of vulnerabilities.