CVE-2025-21947 is a vulnerability identified in the Linux kernel's ksmbd (Kernel SMB Daemon) component, which handles SMB protocol operations within the kernel space. The vulnerability arises from a race condition leading to a type confusion issue during the handling of IPC (Inter-Process Communication) messages, specifically when using the ipc_msg_send_request function. The root cause is that the request handle (req->handle), allocated via ksmbd_acquire_id(&ipc_ida) based on the ida_alloc mechanism, can be reused or duplicated between different IPC requests such as ksmbd_ipc_login_request and FSCTL_PIPE_TRANSCEIVE ioctl calls. This overlap can cause the system to confuse message types, resulting in incorrect message delivery and potentially allowing access to unintended memory regions. Although ksmbd performs type checks on IPC responses, it lacks a mechanism to continue checking subsequent IPC responses after an initial mismatch, which exacerbates the risk of type confusion. This flaw could lead to unauthorized memory access or corruption within the kernel space, potentially enabling privilege escalation or denial of service conditions. The vulnerability affects multiple versions of the Linux kernel as indicated by the repeated commit hashes, and no known exploits have been reported in the wild as of the publication date (April 1, 2025). No CVSS score has been assigned yet, and no official patches or mitigation links are provided in the source information.

For European organizations, this vulnerability poses a significant risk, especially for those relying on Linux servers that utilize the ksmbd service for SMB protocol support, such as file sharing and network resource access. Exploitation could allow attackers to gain unauthorized access to kernel memory, potentially leading to privilege escalation, unauthorized data access, or system instability. This could disrupt critical services, compromise sensitive data, and impact availability. Organizations in sectors such as finance, government, healthcare, and critical infrastructure, which often deploy Linux-based systems for backend services, could face operational disruptions and data breaches. The lack of known exploits currently reduces immediate risk, but the vulnerability's nature suggests that skilled attackers could develop exploits, increasing future threat levels. Additionally, the kernel-level impact means that successful exploitation could bypass many traditional security controls, making detection and remediation more challenging.

Given the kernel-level nature of this vulnerability, European organizations should prioritize the following mitigations: 1) Monitor for and apply official Linux kernel updates or patches addressing CVE-2025-21947 as soon as they become available from trusted Linux distributions or the kernel maintainers. 2) Temporarily disable or restrict the use of ksmbd services or SMB-related kernel modules if feasible, especially on systems where SMB functionality is not critical. 3) Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR), and enable security modules like SELinux or AppArmor to limit the impact of potential exploits. 4) Implement strict access controls and network segmentation to limit exposure of vulnerable SMB services to untrusted networks or users. 5) Increase monitoring and logging of SMB-related kernel activities to detect anomalous behavior indicative of exploitation attempts. 6) Conduct thorough testing in controlled environments before deploying kernel updates to avoid service disruptions. 7) Engage with Linux vendor support channels to obtain timely security advisories and patches.