CVE-2023-52442 is a vulnerability identified in the Linux kernel's implementation of the ksmbd server, which handles SMB (Server Message Block) protocol requests. The vulnerability arises from improper validation of session IDs and tree IDs in compound SMB2 requests. Specifically, the functions smb2_get_msg() used within smb2_get_ksmbd_tcon() and smb2_check_user_session() always return the first SMB2 header in a compound request. If the first command in the compound request is SMB2_TREE_CONNECT_HE, the tree ID check is skipped, effectively bypassing a critical validation step. This flaw allows an attacker to potentially manipulate SMB2 compound requests to bypass tree ID validation, which could lead to unauthorized access to SMB shares or resources on the affected Linux system. The patch addresses this by using ksmbd_req_buf_next() to correctly retrieve the current command in the compound request, ensuring proper validation of session and tree IDs for each command within the compound request. This vulnerability affects Linux kernel versions identified by the commit hash 0626e6641f6b467447c81dd7678a69c66f7746cf and was published on February 21, 2024. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

For European organizations, this vulnerability poses a risk primarily to systems running Linux kernels with the vulnerable ksmbd SMB server implementation, especially those exposing SMB shares internally or externally. Exploitation could allow unauthorized users to bypass access controls on SMB shares, potentially leading to unauthorized data access, data leakage, or lateral movement within corporate networks. This is particularly concerning for enterprises relying on Linux-based file servers or network-attached storage solutions using ksmbd for SMB services. The impact on confidentiality is significant due to possible unauthorized data access. Integrity could also be affected if attackers manipulate files on SMB shares. Availability impact is lower but cannot be ruled out if the vulnerability is leveraged to disrupt SMB services. Since the vulnerability involves session and tree ID validation bypass, attackers might exploit it without needing valid authentication credentials if the SMB service is exposed or accessible. This elevates the risk in environments with weak network segmentation or exposed SMB services. Given the widespread use of Linux servers in European enterprises, including government, finance, and critical infrastructure sectors, the vulnerability could have broad implications if exploited.

European organizations should immediately verify if their Linux systems are running vulnerable kernel versions with ksmbd SMB server enabled. Applying the official Linux kernel patch that corrects the session and tree ID validation logic is the primary mitigation step. Organizations should ensure their Linux distributions are updated to the latest kernel versions containing this fix. Network-level controls should be enforced to restrict SMB traffic to trusted internal networks only, minimizing exposure to untrusted networks or the internet. Implementing strict firewall rules and network segmentation can reduce the attack surface. Additionally, monitoring SMB traffic for unusual compound requests or anomalous session/tree ID usage can help detect exploitation attempts. Organizations should also review SMB share permissions and audit access logs for suspicious activity. Where possible, disabling ksmbd SMB services on Linux systems that do not require SMB functionality can eliminate the risk. Finally, educating system administrators about this vulnerability and encouraging timely patch management practices will strengthen overall security posture.