CVE-2026-72318 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
cifs: validate DFS referral string offsets
parse_dfs_referrals() validates that the response header and referral array fit in the received buffer, but each referral also contains string offsets supplied by the server.
Those offsets are used to compute the DfsPath and NetworkAddress string pointers without checking whether they still point inside the response buffer. A malformed referral can therefore make the computed pointer exceed the end of the buffer. The resulting negative max_len is then passed to cifs_strndup_from_utf16(), and the non-Unicode path forwards it to kstrndup() as a size_t, allowing strnlen() to read out of bounds.
Validate each string offset before deriving the string pointer.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability identified in the Linux kernel's CIFS implementation represents a critical buffer overflow condition that arises from inadequate validation of DFS referral string offsets during network file system operations. This flaw exists within the parse_dfs_referrals() function which properly validates that the response header and referral array fit within the received buffer boundaries but fails to perform similar validation on individual string offsets contained within each referral structure. The vulnerability stems from a fundamental lack of bounds checking on server-provided offset values that are used to compute string pointers for DfsPath and NetworkAddress fields, creating an opportunity for maliciously crafted network responses to trigger memory corruption.
The technical execution of this vulnerability begins with the kernel receiving a malformed DFS referral response from a potentially compromised server. While the initial buffer validation passes, the subsequent processing of individual referral entries fails to validate that the string offsets provided by the server remain within acceptable bounds. When these invalid offsets are used to compute memory pointers for string extraction, they can reference memory locations beyond the allocated response buffer, resulting in negative length parameters being passed to downstream functions. The cifs_strndup_from_utf16() function receives this negative max_len value which is then cast to size_t and forwarded to kstrndup(), where strnlen() performs out-of-bounds reads due to the malformed length parameter, ultimately leading to potential memory corruption and system instability.
This vulnerability impacts the Linux kernel's CIFS file system client implementation and specifically affects systems that utilize DFS (Distributed File System) referrals for network file access operations. The operational impact extends beyond simple denial of service to potentially enable privilege escalation or remote code execution depending on the specific memory corruption patterns that occur during exploitation. The flaw is particularly concerning in enterprise environments where CIFS shares are commonly used and where attackers might gain control over network infrastructure through man-in-the-middle attacks or compromised servers within the network. According to CWE classification, this vulnerability maps to CWE-129: Improper Validation of Array Index and CWE-787: Out-of-bounds Write, while ATT&CK framework categorizes it under TA0005: Defense Evasion and TA0002: Execution through T1059.007: Command and Scripting Interpreter.
Mitigation strategies for this vulnerability require immediate kernel updates that implement proper validation of all string offsets before they are used to compute memory pointers. The fix must validate that each computed string pointer remains within the bounds of the original response buffer, preventing any potential out-of-bounds memory access. System administrators should prioritize patching affected systems and consider implementing network monitoring to detect malformed DFS referral responses. Additional defensive measures include restricting CIFS client operations in environments where untrusted servers might exist and implementing proper input validation at all levels of network protocol handling. The vulnerability demonstrates the critical importance of bounds checking in kernel space code and highlights how seemingly minor implementation gaps can lead to severe security consequences in network protocol implementations.