CVE-2023-39176 in Linux
Summary
by MITRE • 11/18/2024
A flaw was found within the parsing of SMB2 requests that have a transform header in the kernel ksmbd module. The issue results from the lack of proper validation of user-supplied data, which can result in a read past the end of an allocated buffer. An attacker can leverage this to disclose sensitive information on affected installations of Linux. Only systems with ksmbd enabled are vulnerable to this CVE.
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Analysis
by VulDB Data Team • 08/06/2025
The vulnerability identified as CVE-2023-39176 resides within the kernel-based SMB2 implementation known as ksmbd, which provides SMB/CIFS file sharing capabilities on Linux systems. This flaw manifests during the processing of SMB2 requests that contain transform headers, which are used for encryption and signing operations in SMB2 protocol communications. The ksmbd module serves as a kernel-space implementation that handles SMB2/SMB3 protocol requests, making it a critical component for network file sharing services on Linux platforms. Systems utilizing this module for SMB file sharing operations are at risk when running vulnerable kernel versions, particularly those with ksmbd functionality enabled and actively processing network SMB2 requests.
The technical root cause of this vulnerability stems from inadequate input validation within the ksmbd kernel module when processing SMB2 transform headers. Specifically, the module fails to properly validate the length and structure of user-supplied data contained within these headers, leading to a classic buffer over-read condition. When the kernel processes an SMB2 request with a transform header, it attempts to parse the header data without sufficient bounds checking against the allocated buffer space. This validation gap allows an attacker to craft malicious SMB2 requests that cause the kernel to read data beyond the intended buffer boundaries, effectively accessing memory locations that should remain protected from user-space access.
The operational impact of this vulnerability extends beyond simple information disclosure, as it represents a fundamental security weakness in kernel-space memory management. An attacker exploiting this flaw can potentially read sensitive kernel memory contents, including but not limited to authentication credentials, session keys, cryptographic materials, and other confidential data stored in memory. This information disclosure vulnerability is particularly dangerous because it operates at the kernel level, bypassing typical user-space security mechanisms and potentially providing attackers with access to privileged information that could facilitate further exploitation. The vulnerability is specifically limited to systems with ksmbd enabled, making it a targeted issue for Linux systems configured to provide SMB file sharing services through this kernel module.
Mitigation strategies for CVE-2023-39176 should prioritize immediate patching of affected kernel versions, as this represents a critical security flaw requiring kernel-level fixes. Organizations should disable ksmbd functionality on systems where it is not strictly required, particularly in environments where SMB file sharing is not essential. Network segmentation and access controls should be implemented to limit exposure to potentially malicious SMB2 requests, while monitoring systems should be configured to detect unusual SMB2 traffic patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-129, which describes improper validation of input length, and represents a technique that could enable adversaries to access sensitive data through kernel memory manipulation, consistent with ATT&CK technique T1005 for data from local system. System administrators should also consider implementing network-based intrusion detection systems to monitor for suspicious SMB2 transform header patterns that could indicate exploitation attempts, while maintaining up-to-date security patches for all kernel components that handle network protocol processing.