CVE-2023-38431 in Linux
Summary
by MITRE • 07/18/2023
An issue was discovered in the Linux kernel before 6.3.8. fs/smb/server/connection.c in ksmbd does not validate the relationship between the NetBIOS header's length field and the SMB header sizes, via pdu_size in ksmbd_conn_handler_loop, leading to an out-of-bounds read.
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Analysis
by VulDB Data Team • 08/06/2023
The vulnerability identified as CVE-2023-38431 represents a critical out-of-bounds read flaw within the Linux kernel's ksmbd implementation that affects versions prior to 6.3.8. This issue resides in the file system subsystem specifically within the SMB server component located at fs/smb/server/connection.c. The vulnerability stems from insufficient validation mechanisms that fail to properly verify the relationship between the NetBIOS header's length field and the SMB header sizes during protocol processing. The ksmbd_conn_handler_loop function serves as the primary execution context where this validation failure occurs, creating a pathway for malicious actors to exploit the kernel's SMB implementation.
The technical nature of this vulnerability places it squarely within the realm of buffer overflow conditions and memory corruption issues as classified by CWE-129. The flaw manifests when the kernel processes SMB protocol requests without adequate bounds checking on the pdu_size parameter, which represents the protocol data unit size in the SMB connection handling loop. This allows an attacker to craft specially formatted SMB packets that contain malformed NetBIOS header length fields, causing the kernel to read memory beyond the intended buffer boundaries. The out-of-bounds read can potentially expose sensitive kernel memory contents, leading to information disclosure or even privilege escalation depending on the specific memory locations accessed.
From an operational perspective, this vulnerability poses significant risks to systems running affected Linux kernel versions with SMB server functionality enabled. The attack surface includes any system that utilizes ksmbd for SMB file sharing services, which could encompass enterprise file servers, network attached storage devices, or any Linux system configured to act as an SMB server. The exploitation potential aligns with ATT&CK technique T1059.007 for command and script injection, as successful exploitation could enable remote code execution capabilities. The vulnerability's impact extends beyond simple information disclosure, as it could potentially allow attackers to gather kernel memory layout information that would facilitate more sophisticated attacks.
Mitigation strategies for CVE-2023-38431 primarily focus on immediate kernel version upgrades to 6.3.8 or later, which contain the necessary patches to address the validation gap in the SMB connection handling code. System administrators should also implement network segmentation and access controls to limit exposure of SMB services to trusted networks only, as recommended by the NIST Cybersecurity Framework. Additional defensive measures include monitoring for unusual SMB traffic patterns and implementing network intrusion detection systems that can identify malformed SMB packets attempting to exploit this vulnerability. Organizations should also consider disabling SMB server functionality if it is not required for their operations, following the principle of least privilege as outlined in the ISO/IEC 27001 information security standard. The patch addresses the core validation issue by introducing proper bounds checking between the NetBIOS header length field and SMB header sizes, ensuring that pdu_size values remain within acceptable parameter ranges before memory access operations occur.