CVE-2025-21762 is a high-severity vulnerability affecting the Linux kernel, specifically within the ARP (Address Resolution Protocol) implementation. The flaw arises in the arp_xmit() function, which is responsible for transmitting ARP packets. The vulnerability is due to the lack of proper Read-Copy-Update (RCU) protection when arp_xmit() is called. RCU is a synchronization mechanism used in the Linux kernel to safely handle concurrent read and update operations on shared data structures. Without RCU protection or RTNL (routing netlink) lock, the arp_xmit() function may operate on data structures that have been freed or modified concurrently, leading to a Use-After-Free (UAF) condition (CWE-416). This UAF can cause memory corruption, potentially allowing an attacker with limited privileges (local access with low privileges) to escalate their privileges, execute arbitrary code within the kernel context, or cause a denial of service by crashing the kernel. The vulnerability requires local access with low privileges and does not require user interaction, but exploitation complexity is low given the direct kernel memory corruption. The CVSS v3.1 score of 7.8 reflects the high impact on confidentiality, integrity, and availability, with low attack complexity and limited privileges required. The affected versions are identified by a specific commit hash, indicating the vulnerability exists in certain recent Linux kernel versions prior to the patch. No known exploits are currently reported in the wild, but the nature of the vulnerability makes it a significant risk for systems running vulnerable Linux kernels, especially those exposed to untrusted local users or processes. The patch involves adding proper RCU protection to the arp_xmit() function to prevent the UAF condition.

For European organizations, this vulnerability poses a significant risk, particularly for enterprises and service providers relying on Linux-based infrastructure, including servers, network devices, and embedded systems. Successful exploitation could lead to privilege escalation, allowing attackers to gain root-level access, compromising system confidentiality and integrity. This could result in unauthorized data access, manipulation, or destruction, and potentially disrupt critical services through denial of service. Given the widespread use of Linux in European data centers, cloud environments, and telecommunications infrastructure, the vulnerability could impact a broad range of sectors including finance, healthcare, government, and industrial control systems. The risk is heightened in multi-tenant environments where untrusted users or containers share the same kernel. Additionally, the vulnerability could be leveraged as a stepping stone for lateral movement within networks. Although no exploits are currently known in the wild, the high severity and relatively low complexity of exploitation necessitate urgent attention to prevent potential future attacks.

European organizations should prioritize patching affected Linux kernel versions as soon as updates become available from their distribution vendors. Since the vulnerability is due to missing RCU protection in arp_xmit(), applying the official kernel patches or upgrading to a fixed kernel version is the most effective mitigation. Until patches are applied, organizations should restrict local access to trusted users only, enforce strict access controls, and monitor for unusual kernel crashes or suspicious local activity that could indicate exploitation attempts. Employing kernel hardening techniques such as SELinux or AppArmor can help limit the impact of a successful exploit. Network segmentation and isolation of critical Linux systems can reduce the attack surface. Additionally, organizations should maintain up-to-date intrusion detection systems capable of identifying anomalous kernel behavior. For environments using containers or virtual machines, ensuring that guest kernels are patched is critical, as container escapes could leverage this vulnerability. Regular vulnerability scanning and compliance checks should include verification of kernel patch levels related to this CVE.