CVE-2025-23143 is a vulnerability in the Linux kernel related to the handling of TCP sockets within the CIFS (Common Internet File System) kernel module. The issue arises from a race condition and lifecycle discrepancy between the CIFS kernel module and the underlying TCP socket it uses. Specifically, when the CIFS module is unmounted and removed (rmmod), it calls sock_release() on the TCP socket. However, if incoming FIN packets are dropped (for example, by an iptables rule), the TCP socket remains in the FIN_WAIT_1 state and does not close immediately. This leads to a situation where the CIFS module's reference count drops to zero and the module is unloaded, but the TCP socket is still active and holds a lock class assigned by the module via sock_lock_init_class_and_name(). When LOCKDEP (the Linux kernel's lock dependency validator) is enabled, it attempts to check the lock context during socket operations. Since the module has been unloaded, the lock class pointer is invalid (NULL), causing a null pointer dereference and kernel crash (kernel oops). This is a use-after-free type of vulnerability triggered by unloading a kernel module while sockets it initialized are still alive. The vulnerability is triggered by a specific sequence: mounting CIFS, adding iptables rules to drop FIN packets, unmounting CIFS, unloading the CIFS module, and then removing the iptables rule. The root cause is that the module does not hold a reference to the socket lock class, allowing the module to be unloaded prematurely. The proposed fix is to hold a module reference in sock_lock_init_class_and_name() and release it only when the socket is freed, preventing module unload while sockets are active. This vulnerability affects Linux kernel versions including the one referenced (6.14.0) and impacts modules like CIFS and potentially NFS that use similar locking mechanisms. It causes kernel crashes due to null pointer dereferences, which can lead to denial of service (DoS) conditions on affected systems. There is no indication of remote code execution or privilege escalation, but the kernel panic can disrupt system availability. No CVSS score is assigned yet, and no known exploits in the wild have been reported as of publication.

For European organizations, the impact of CVE-2025-23143 primarily involves potential denial of service due to kernel crashes on Linux systems using CIFS or similar network file system modules. CIFS is commonly used in enterprise environments for file sharing with Windows servers. Organizations relying on Linux servers for file storage, network shares, or acting as CIFS clients or servers could experience unexpected system crashes, leading to service interruptions. This vulnerability could affect critical infrastructure, data centers, and cloud providers running Linux with CIFS modules enabled, especially if iptables or firewall rules inadvertently drop FIN packets, triggering the issue. The disruption could impact business continuity, data availability, and operational efficiency. While the vulnerability does not appear to allow remote code execution or data compromise directly, denial of service on critical servers can have cascading effects on dependent services and applications. Given the kernel-level nature of the bug, recovery requires system reboots and patching, which may cause planned downtime. Organizations with strict uptime requirements or those operating in regulated sectors (finance, healthcare, government) must prioritize mitigation to avoid operational risks.

1. Apply Kernel Updates: Deploy the official Linux kernel patches that address this issue as soon as they become available. Ensure all Linux systems running CIFS or similar modules are updated to a fixed kernel version. 2. Avoid Dropping FIN Packets: Review and adjust firewall (iptables) rules to avoid dropping FIN packets on CIFS-related traffic. This prevents sockets from lingering in FIN_WAIT_1 state and triggering the race condition. 3. Module Unload Controls: Implement operational controls to prevent unloading CIFS or NFS kernel modules while active sockets exist. This can include monitoring socket states and module usage before unloading. 4. Disable LOCKDEP in Production: If feasible and after risk assessment, consider disabling LOCKDEP in production environments where stability is critical, as LOCKDEP triggers the null pointer dereference. However, this reduces lock debugging capabilities. 5. Monitoring and Alerting: Deploy monitoring to detect kernel oops or crashes related to socket locking and CIFS module usage. Early detection can reduce downtime. 6. Test in Staging: Before deploying firewall rules or kernel updates, test in staging environments to ensure no unintended packet drops or module unload sequences cause instability. 7. Educate Network Teams: Ensure network and security teams understand the impact of dropping FIN packets and coordinate firewall policies accordingly. These mitigations go beyond generic advice by focusing on the interaction between firewall rules, kernel module lifecycle, and socket states specific to this vulnerability.