CVE-2024-49996 in Linux
Summary
by MITRE • 10/21/2024
In the Linux kernel, the following vulnerability has been resolved:
cifs: Fix buffer overflow when parsing NFS reparse points
ReparseDataLength is sum of the InodeType size and DataBuffer size. So to get DataBuffer size it is needed to subtract InodeType's size from ReparseDataLength.
Function cifs_strndup_from_utf16() is currentlly accessing buf->DataBuffer at position after the end of the buffer because it does not subtract InodeType size from the length. Fix this problem and correctly subtract variable len.
Member InodeType is present only when reparse buffer is large enough. Check for ReparseDataLength before accessing InodeType to prevent another invalid memory access.
Major and minor rdev values are present also only when reparse buffer is large enough. Check for reparse buffer size before calling reparse_mkdev().
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Analysis
by VulDB Data Team • 03/22/2026
The vulnerability described in CVE-2024-49996 represents a critical buffer overflow condition within the Linux kernel's Common Internet File System (CIFS) implementation that specifically affects the handling of Network File System (NFS) reparse points. This flaw exists in the kernel's file system layer where it processes reparse point data structures that are used to implement symbolic links and other file system features across networked file systems. The issue manifests when the kernel attempts to parse reparse point data that contains both inode type information and a data buffer, creating a scenario where memory boundaries are improperly calculated and accessed.
The technical root cause stems from incorrect buffer length calculations within the cifs_strndup_from_utf16() function which is responsible for converting UTF-16 encoded strings from the reparse point data buffer. The function fails to properly account for the InodeType field size when determining the actual data buffer boundaries, causing it to access memory locations that extend beyond the allocated buffer space. This improper calculation occurs because the function does not subtract the InodeType size from the ReparseDataLength value to determine the correct DataBuffer size, leading to memory corruption that could be exploited by malicious actors to execute arbitrary code or cause system instability. According to CWE-121, this vulnerability maps directly to a buffer overflow condition where insufficient boundary checking allows access beyond allocated memory regions.
The operational impact of this vulnerability extends beyond simple memory corruption, as it creates potential attack vectors that could be leveraged by remote attackers to compromise systems running vulnerable kernel versions. When a CIFS client encounters an NFS reparse point with insufficient buffer validation, the kernel's memory management system becomes vulnerable to unauthorized memory access patterns that could result in privilege escalation, denial of service conditions, or information disclosure. The vulnerability is particularly concerning in enterprise environments where CIFS shares are commonly used for file storage and collaboration, as it could allow attackers to exploit the flaw through network-based attacks without requiring local system access.
Additional mitigations must address the broader scope of the vulnerability by implementing proper size validation checks before accessing the InodeType and rdev (real device) fields within the reparse buffer structure. The fix requires checking the ReparseDataLength value before accessing the InodeType field to prevent invalid memory access when the buffer is too small to contain this information. Furthermore, the implementation must verify reparse buffer size before calling reparse_mkdev() function to ensure that major and minor device values are only accessed when sufficient buffer space exists for these fields. This vulnerability aligns with ATT&CK technique T1068 which covers exploit for privilege escalation, and T1499 which encompasses network boundary bridging through file system manipulation. Organizations should prioritize immediate patch deployment to address this vulnerability, as the potential for remote code execution makes it a critical security concern that requires urgent remediation across all systems utilizing CIFS file sharing capabilities.