CVE-2025-21785 is a vulnerability identified in the Linux kernel specifically affecting the arm64 architecture's cacheinfo subsystem. The issue arises from an out-of-bounds write to the cacheinfo array during the detection and population of cache information. The root cause is a logic error in the loop responsible for populating cache details: while the loop includes a bounds check based on the array size, it fails to correctly handle cache levels that have separate data and instruction caches. Instead of incrementing the index for each populated cache leaf (which can be multiple per level), it increments per populated level, leading to potential writes beyond the allocated array bounds. This can cause memory corruption within the kernel space. The vulnerability was addressed by modifying the index increment logic to account for each populated leaf, preventing out-of-bounds writes. The affected versions are tied to a specific commit hash (5d425c18653731af62831d30a4fa023d532657a9), indicating a particular kernel revision or patch level. No known exploits are reported in the wild as of the publication date (February 27, 2025), and no CVSS score has been assigned yet. The vulnerability is technical and low-level, impacting kernel memory integrity on arm64 Linux systems, which are increasingly common in servers, embedded devices, and cloud infrastructure.

For European organizations, the impact of CVE-2025-21785 depends on their deployment of arm64-based Linux systems. The vulnerability can lead to kernel memory corruption, which may cause system instability, crashes, or potentially be leveraged for privilege escalation or arbitrary code execution if exploited by a local attacker. This could compromise confidentiality, integrity, and availability of affected systems. Organizations running arm64 Linux servers, especially in cloud environments or critical infrastructure, could face service disruptions or security breaches. Given the kernel-level nature, exploitation could allow attackers to bypass security controls, access sensitive data, or disrupt operations. However, the lack of known exploits and the requirement for local access or specific conditions to trigger the bug may limit immediate risk. Still, the increasing adoption of arm64 architecture in Europe’s data centers and edge computing makes timely patching important to prevent future exploitation.

European organizations should prioritize updating their Linux kernels to versions that include the fix for CVE-2025-21785. Since the vulnerability is in the kernel's cacheinfo subsystem, patching the kernel is the only effective mitigation. Organizations should: 1) Identify all arm64 Linux systems in their environment, including servers, embedded devices, and cloud instances. 2) Apply vendor-supplied kernel updates or patches that address this vulnerability promptly. 3) For systems where immediate patching is not feasible, restrict local user access and enforce strict privilege separation to reduce exploitation risk. 4) Monitor system logs and kernel crash reports for anomalies that might indicate exploitation attempts. 5) Engage with Linux distribution vendors and cloud providers to confirm patch availability and deployment timelines. 6) Incorporate this vulnerability into vulnerability management and incident response plans to ensure rapid detection and remediation.