CVE-2023-38429 in Linux
Summary
by MITRE • 07/18/2023
An issue was discovered in the Linux kernel before 6.3.4. fs/ksmbd/connection.c in ksmbd has an off-by-one error in memory allocation (because of ksmbd_smb2_check_message) that may lead to out-of-bounds access.
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Analysis
by VulDB Data Team • 08/06/2023
The vulnerability identified as CVE-2023-38429 represents a critical memory corruption flaw within the Linux kernel's ksmbd subsystem, which is responsible for implementing the SMB2/SMB3 protocol for file sharing services. This issue affects Linux kernel versions prior to 6.3.4 and specifically targets the fs/ksmbd/connection.c file where a fundamental programming error occurs during message processing. The flaw manifests as an off-by-one error in memory allocation logic that directly impacts how the ksmbd server handles incoming SMB2 protocol messages, creating a pathway for potentially exploitable memory access violations.
The technical root cause of this vulnerability stems from the ksmbd_smb2_check_message function which incorrectly calculates memory requirements for processing SMB2 protocol messages. This miscalculation occurs during the validation phase of SMB2 message handling where the system allocates memory based on flawed boundary calculations. When the system processes certain malformed or specially crafted SMB2 messages, the off-by-one error results in insufficient memory allocation, causing subsequent memory access operations to traverse beyond allocated buffer boundaries. This type of vulnerability falls under the CWE-129 weakness category, which specifically addresses improper validation of array indices and buffer bounds, making it susceptible to out-of-bounds memory access patterns that can lead to arbitrary code execution or system instability.
The operational impact of this vulnerability extends beyond simple memory corruption, as it creates potential attack vectors for remote code execution within systems running vulnerable kernel versions. When exploited, the out-of-bounds memory access can lead to denial of service conditions, data corruption, or more severe exploitation scenarios where attackers might leverage the memory corruption to execute arbitrary code with kernel privileges. The ksmbd subsystem serves as a critical component for file sharing in Linux environments, particularly in enterprise and server deployments where SMB protocol support is essential. Attackers could potentially craft malicious SMB2 messages that trigger this vulnerability during normal file sharing operations, making it particularly dangerous in networked environments where SMB services are exposed to external traffic.
Security professionals should prioritize patching affected systems with kernel versions 6.3.4 or later, as this vulnerability represents a significant risk to system integrity and availability. The mitigation strategy involves immediate kernel updates to ensure the corrected memory allocation logic is in place, along with network segmentation to limit exposure of SMB services to untrusted networks. Organizations should also implement monitoring for unusual SMB2 protocol traffic patterns that might indicate exploitation attempts, as the vulnerability's impact is most pronounced during active SMB2 message processing. From an attacker perspective, this vulnerability aligns with ATT&CK technique T1059.007 for command and control communications through SMB protocols, making it particularly concerning for environments where SMB services are not properly secured or isolated from external networks. The vulnerability's presence in the kernel's core file sharing subsystem underscores the importance of maintaining up-to-date security patches and implementing comprehensive security monitoring for critical infrastructure components.