CVE-2023-52757 is a vulnerability identified in the Linux kernel's SMB (Server Message Block) client implementation, specifically related to the handling of MID (Multiplex ID) references and locking mechanisms. The issue arises from the use of spinlocks around the release of MID references, where the release_mid() function improperly calls kref_put() on the MID's reference count while holding the server's mid_lock spinlock. This locking strategy can lead to a potential deadlock scenario involving two CPUs: one executing cifs_demultiplex_thread() and the other running cifs_debug_data_proc_show(). The deadlock occurs due to a circular lock dependency between server->mid_lock and cifs_tcp_ses_lock spinlocks. Additionally, the vulnerability hints at a possible use-after-free bug if callers do not hold a reference to the MID, although this is mitigated by the current design where all release_mid() callers hold such a reference. The fix involves removing the kref_put() call under the mid_lock spinlock, thereby eliminating the deadlock risk and preventing potential use-after-free conditions. This vulnerability affects Linux kernel versions identified by the commit hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 and was published on May 21, 2024. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet.

For European organizations, this vulnerability primarily threatens the stability and reliability of Linux-based systems that utilize SMB client functionality, which is common in enterprise environments for file sharing and network resource access. A deadlock in kernel space can cause system hangs or crashes, leading to denial of service (DoS) conditions affecting critical infrastructure, servers, and network appliances. This can disrupt business operations, especially in sectors reliant on continuous file access and network communication, such as finance, manufacturing, and public services. Although no direct confidentiality or integrity breach is indicated, the potential for system unavailability can have significant operational and financial consequences. Moreover, if the use-after-free scenario were to be exploited, it could lead to memory corruption, potentially enabling privilege escalation or arbitrary code execution, although this is not confirmed here. The absence of known exploits reduces immediate risk, but the vulnerability's presence in the widely deployed Linux kernel necessitates prompt attention.

European organizations should prioritize updating their Linux kernel to the patched versions that remove the problematic spinlock usage in the SMB client code. Specifically, kernel maintainers and system administrators must apply the fix that eliminates the kref_put() call under the mid_lock spinlock to prevent deadlocks. Organizations should audit their systems to identify Linux hosts running SMB client services and verify kernel versions against the affected commit. In environments where immediate patching is not feasible, monitoring system logs for symptoms of deadlocks or hangs related to SMB operations can provide early warning. Additionally, implementing kernel live patching solutions where supported can reduce downtime. Network segmentation and limiting SMB client usage to trusted internal networks can reduce exposure. Finally, maintaining robust backup and recovery procedures will mitigate the impact of potential system outages.