CVE-2023-52447 is a vulnerability in the Linux kernel related to the handling of inner maps within BPF (Berkeley Packet Filter) map arrays or hash tables. Specifically, when updating or deleting an inner map, the kernel may prematurely free the inner map object while it is still being accessed by BPF programs, leading to a use-after-free condition. This occurs because the reference counter for the inner map is decremented directly without properly deferring the free operation until after a safe grace period. The flaw stems from the fact that most map_free() callbacks do not utilize synchronize_rcu() or equivalent mechanisms to wait for the completion of all ongoing references before freeing memory. Consequently, BPF programs accessing the inner map after it has been freed may experience memory corruption, potentially leading to arbitrary code execution or kernel crashes. The fix involves deferring the free operation by invoking bpf_map_free_deferred(), which waits for both a standard RCU grace period and a task trace RCU grace period before releasing the last reference to the map. This is implemented using call_rcu() and call_rcu_tasks_trace(), ensuring safe reclamation of resources. The patch also optimizes memory usage by sharing storage between the rcu_head and work fields in the bpf_map structure. This vulnerability is classified under CWE-416 (Use After Free) and has a CVSS v3.1 score of 6.7, indicating a medium severity level. Exploitation requires local privileges with high-level permissions (PR:H), no user interaction, and the attack vector is local (AV:L). There are no known exploits in the wild at the time of publication.

For European organizations, this vulnerability poses a significant risk primarily to systems running vulnerable Linux kernel versions that utilize BPF programs, which are commonly employed for network monitoring, security enforcement, and performance tracing. Successful exploitation could allow a privileged local attacker to execute arbitrary code within the kernel context, leading to full system compromise, data breaches, or denial of service through kernel crashes. This is particularly critical for infrastructure providers, cloud service operators, and enterprises relying on Linux-based servers and network appliances. The use-after-free condition could also be leveraged to bypass security controls implemented via BPF, undermining network security monitoring and enforcement mechanisms. Given the widespread adoption of Linux across European public and private sectors, including critical infrastructure, this vulnerability could impact a broad range of organizations if unpatched. However, exploitation complexity is moderate due to the requirement for high privileges and local access, limiting the threat primarily to insiders or attackers who have already gained some level of system access.

European organizations should prioritize patching Linux kernel versions to the fixed releases that address CVE-2023-52447 as soon as they become available. In the interim, organizations should: 1) Restrict and monitor privileged user access to limit the potential for local exploitation. 2) Employ kernel live patching solutions where feasible to minimize downtime while applying security fixes. 3) Audit and restrict the use of custom or third-party BPF programs, ensuring only trusted code is executed. 4) Monitor system logs and kernel messages for unusual behavior or crashes related to BPF map operations. 5) Implement strict network segmentation and host-based intrusion detection to detect and contain potential exploitation attempts. 6) Educate system administrators about the risks associated with BPF and the importance of timely patching. These steps go beyond generic advice by focusing on controlling the attack surface related to BPF usage and minimizing privileged access that could be leveraged for exploitation.