CVE-2025-37926 is a use-after-free (UAF) vulnerability identified in the Linux kernel's ksmbd component, which handles SMB (Server Message Block) protocol services. The vulnerability arises from a race condition between the functions ksmbd_session_rpc_open() and __session_rpc_close(). Specifically, the issue occurs because these two functions can concurrently access and modify session-related data without proper synchronization, leading to a use-after-free scenario. This means that a session object may be freed while still being accessed, potentially allowing an attacker to execute arbitrary code, cause a denial of service (system crash), or escalate privileges. The fix involves introducing an rpc_lock to the session object to serialize access and prevent concurrent modification, thereby eliminating the race condition. The vulnerability affects certain versions of the Linux kernel identified by specific commit hashes, and it was publicly disclosed on May 20, 2025. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet.

For European organizations, this vulnerability poses a significant risk, especially for those relying on Linux servers providing SMB services via ksmbd, such as file sharing and network resource access. Exploitation could lead to unauthorized code execution or denial of service, impacting confidentiality, integrity, and availability of critical systems. This could disrupt business operations, lead to data breaches, or facilitate lateral movement within networks. Given the widespread use of Linux in enterprise environments, cloud infrastructures, and critical infrastructure sectors across Europe, the potential impact is broad. Organizations in sectors like finance, healthcare, manufacturing, and government are particularly at risk due to their reliance on secure file sharing and network services. The absence of known exploits suggests a window of opportunity for proactive patching before active exploitation occurs.

European organizations should prioritize applying the patch that introduces the rpc_lock to the ksmbd session object as soon as it becomes available. In the interim, organizations can mitigate risk by limiting exposure of SMB services to untrusted networks, employing network segmentation to isolate vulnerable systems, and monitoring for unusual activity related to SMB sessions. Additionally, implementing strict access controls and using intrusion detection systems tuned to detect abnormal SMB traffic patterns can help identify attempted exploitation. Regularly updating Linux kernel versions and subscribing to vendor security advisories will ensure timely awareness of patches. For environments where immediate patching is not feasible, disabling ksmbd or SMB services temporarily can reduce attack surface. Finally, conducting internal audits to identify systems running affected kernel versions will help prioritize remediation efforts.