CVE-2025-25565 is a critical buffer overflow vulnerability identified in SoftEther VPN version 5.02.5187, specifically within the Command.c source file. The vulnerability arises in the PtMakeCert and PtMakeCert2048 functions, which are responsible for certificate generation. A buffer overflow occurs when these functions improperly handle input strings, allowing an attacker to overwrite memory beyond the allocated buffer. This can lead to arbitrary code execution, denial of service, or system compromise. The CVSS 3.1 base score is 9.8, indicating a critical severity with network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), and high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). However, the supplier disputes the vulnerability's practical exploitability, arguing that the vulnerable code path only permits a user to attack themselves by entering a long string on a command line, implying that remote exploitation or exploitation by other users is not feasible. Despite this, the vulnerability remains critical due to the potential for local exploitation without authentication or user interaction. SoftEther VPN is an open-source, multi-protocol VPN solution widely used for secure remote access. The affected functions relate to certificate creation, a sensitive operation that, if exploited, could undermine the VPN's security guarantees. No patches or fixes are currently linked, and no known exploits are reported in the wild. The vulnerability is classified under CWE-120 (Classic Buffer Overflow), a common and dangerous software weakness. Given the nature of the vulnerability and the critical CVSS score, organizations using SoftEther VPN 5.02.5187 should consider this a serious risk, especially if the software is exposed to untrusted users or environments where local users might attempt exploitation.

For European organizations, the impact of CVE-2025-25565 could be significant if SoftEther VPN 5.02.5187 is deployed in environments where multiple users have local access or where the VPN server is accessible to untrusted users. Exploitation could lead to full system compromise, allowing attackers to execute arbitrary code, steal sensitive data, or disrupt VPN services. This could result in loss of confidentiality of communications, integrity breaches of network traffic, and denial of service, impacting business continuity and regulatory compliance (e.g., GDPR). However, the supplier's claim that exploitation requires self-attack via command line input limits the threat to local users attacking their own session, reducing the risk of remote exploitation. Still, insider threats or compromised local accounts could leverage this vulnerability. The lack of known exploits in the wild reduces immediate risk but does not eliminate the potential for future attacks. Organizations relying on SoftEther VPN for secure remote access should assess their exposure, especially in multi-tenant or shared environments, and consider the risk of local privilege escalation or lateral movement within their networks.

1. Immediate mitigation should include restricting local access to systems running SoftEther VPN 5.02.5187 to trusted personnel only, minimizing the risk of local exploitation. 2. Monitor and audit command line usage related to certificate generation functions (PtMakeCert and PtMakeCert2048) to detect anomalous or excessively long input strings that could indicate attempted exploitation. 3. Implement strict access controls and user permissions to prevent unauthorized users from executing commands that invoke vulnerable functions. 4. Consider deploying SoftEther VPN in isolated or hardened environments where local user privileges are tightly controlled. 5. Engage with SoftEther VPN developers or community to obtain patches or updates addressing this vulnerability as soon as they become available. 6. As a longer-term measure, evaluate alternative VPN solutions with active maintenance and security support if patching is delayed. 7. Employ host-based intrusion detection systems (HIDS) to detect abnormal process behavior or memory corruption attempts related to the VPN service. 8. Educate system administrators and users about the risks of executing untrusted commands or scripts within the VPN environment.