CVE-2025-22077 is a vulnerability in the Linux kernel related to the handling of TCP socket timers and network namespace (netns) references within the SMB/CIFS client implementation. The issue arises from a flawed fix that attempted to resolve a null pointer dereference in LOCKDEP (a kernel locking correctness validator) but inadvertently reintroduced a use-after-free condition and socket state management problems. Specifically, when a CIFS connection reconnects, the TCP socket transitions to the FIN_WAIT_1 state. Normally, the kernel's tcp_close() function stops all timers associated with the socket to gracefully close the connection. However, if an incoming FIN packet is lost and the peer aborts the connection, the socket can remain stuck in FIN_WAIT_1 indefinitely. This leads to socket leaks that can accumulate up to the limit set by net.ipv4.tcp_max_orphans, potentially exhausting system resources. The root cause is that the kernel socket does not maintain a reference count to its network namespace (sk_net_refcnt), allowing the netns to be freed while timers are still active, resulting in use-after-free conditions. The vulnerability stems from reverting a prior commit that had correctly added a netns reference to the CIFS client socket, which was the proper fix. The flawed revert reintroduced the problem by removing this reference, causing TCP socket timers to be stopped prematurely and the socket to leak. The vulnerability also highlights the complexity of managing socket lifetimes and netns lifetimes, especially for TCP connections that require timers to close gracefully even after socket close() calls. The report suggests that the correct approach is to maintain a netns reference count on the socket to prevent premature freeing and to prevent module unloads by managing LOCKDEP keys properly. This vulnerability affects multiple Linux kernel versions identified by specific commits and is currently published without a CVSS score or known exploits in the wild.

For European organizations, this vulnerability poses a significant risk primarily to systems running Linux kernels with the affected commits, especially those utilizing SMB/CIFS clients for file sharing and network storage. The socket leak in FIN_WAIT_1 state can lead to resource exhaustion on critical servers, causing denial of service (DoS) conditions. This can disrupt file sharing services, impacting business operations reliant on networked storage or SMB-based applications. The use-after-free condition could potentially be leveraged for local privilege escalation or kernel crashes, though no direct exploit is known yet. Given the widespread use of Linux in European data centers, cloud infrastructures, and enterprise environments, the vulnerability could affect a broad range of servers and network devices. The issue is particularly relevant for organizations with complex network namespace configurations, containerized environments, or those employing advanced network virtualization, as improper netns reference handling can lead to stability and security issues. The vulnerability also complicates kernel module management and could affect the reliability of network services. While no active exploits are reported, the potential for denial of service and system instability makes timely mitigation critical to maintain operational continuity and security posture.

European organizations should prioritize updating their Linux kernels to versions that reintroduce the correct fix, which involves maintaining a netns reference count on CIFS client sockets to prevent socket leaks and use-after-free conditions. Since no official patch links are provided, organizations should monitor Linux kernel mailing lists and vendor advisories for backported fixes or updated kernel releases addressing CVE-2025-22077. In the interim, system administrators should: 1) Monitor TCP socket states, particularly FIN_WAIT_1, to detect abnormal socket accumulation that may indicate exploitation or resource leaks. 2) Adjust the net.ipv4.tcp_max_orphans sysctl parameter cautiously to prevent resource exhaustion but avoid masking the underlying issue. 3) Review and harden network namespace and container configurations to ensure proper cleanup of network resources. 4) Limit SMB/CIFS client usage on critical systems or isolate vulnerable systems until patched. 5) Employ kernel lockdown features or module signing to prevent unauthorized module unloads that might trigger LOCKDEP-related issues. 6) Engage with Linux distribution vendors for security advisories and apply recommended kernel updates promptly. These steps go beyond generic advice by focusing on kernel-level resource management, network namespace hygiene, and proactive monitoring of TCP socket states relevant to this vulnerability.