CVE-2025-25566 is a memory leak vulnerability identified in SoftEtherVPN version 5.02.5187. The vulnerability arises from the UnixMemoryAlloc function, which improperly manages memory allocation, leading to a leak. Memory leaks occur when allocated memory is not properly released back to the system, causing gradual exhaustion of available memory resources. In this case, an attacker can exploit the vulnerability to cause a denial of service (DoS) condition by forcing the application to consume increasing amounts of memory, potentially leading to service degradation or crash. However, the supplier disputes the severity of this issue, noting that the leak is limited to a single allocation of a few hundred bytes and occurs only when using a command-line tool, which may limit the practical exploitability and impact. The CVSS v3.1 base score is 5.6 (medium severity), reflecting a network attack vector (AV:N) but requiring high attack complexity (AC:H), no privileges (PR:N), and no user interaction (UI:N). The impact affects confidentiality, integrity, and availability at a low level. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability is classified under CWE-401 (Improper Release of Memory Before Removing Last Reference). Given the limited scope and the supplier's dispute, this vulnerability is unlikely to be critical but still warrants attention in environments where SoftEtherVPN 5.02.5187 is deployed, especially in automated or high-load scenarios where memory leaks can accumulate over time.

For European organizations, the impact of CVE-2025-25566 is primarily related to availability degradation of SoftEtherVPN services. SoftEtherVPN is an open-source VPN solution used by various organizations for secure remote access. A memory leak, even if limited, can cause gradual resource exhaustion, potentially leading to service interruptions or crashes under sustained exploitation. This can disrupt secure communications, remote work capabilities, and access to internal resources, which is critical for business continuity. Confidentiality and integrity impacts are low but not negligible, as denial of service can indirectly affect security operations. The medium CVSS score reflects that exploitation is possible remotely without privileges but requires high attack complexity, reducing the likelihood of widespread automated attacks. European organizations relying on SoftEtherVPN for critical infrastructure or sensitive communications should consider the risk, especially in sectors like finance, government, and healthcare where VPN availability is essential. The lack of known exploits and limited memory leak size reduces immediate threat but does not eliminate risk from targeted attackers or combined attack vectors.

1. Monitor memory usage of SoftEtherVPN instances closely, especially on Unix/Linux systems, to detect abnormal increases that may indicate exploitation of the memory leak. 2. Limit exposure of the SoftEtherVPN command-line tools to untrusted users or networks, as the vulnerability is triggered via command-line operations. 3. Implement strict network segmentation and firewall rules to restrict access to VPN management interfaces. 4. Regularly update and patch SoftEtherVPN software; although no patch is currently linked, maintain vigilance for vendor updates addressing this issue. 5. Employ resource limits (e.g., cgroups or ulimit on Linux) to constrain memory usage of the VPN process, preventing system-wide impact from leaks. 6. Consider alternative VPN solutions or versions if the risk is unacceptable and no timely patch is available. 7. Conduct penetration testing and vulnerability assessments focusing on VPN infrastructure to identify potential exploitation paths. 8. Maintain incident response readiness to quickly address any denial of service or service degradation events related to VPN availability.