CVE-2025-4079 is a buffer overflow vulnerability identified in PCMan FTP Server versions up to 2.0.7, specifically within an unspecified function of the RENAME command handler component. This vulnerability allows an attacker to remotely trigger a buffer overflow condition by manipulating the RENAME command, which is part of the FTP protocol used to rename files on the server. The overflow occurs due to improper handling of input data length, leading to memory corruption. Since the vulnerability can be exploited remotely without requiring authentication or user interaction, it poses a significant risk to exposed FTP servers running the affected versions. The disclosed exploit enables attackers to potentially execute arbitrary code, cause denial of service (DoS) by crashing the server, or manipulate files on the server, impacting confidentiality, integrity, and availability. The CVSS 4.0 base score is 6.9 (medium severity), reflecting the network attack vector, low attack complexity, no privileges or user interaction required, but limited impact on confidentiality, integrity, and availability. No known exploits in the wild have been reported yet, but public disclosure increases the risk of exploitation. The vulnerability affects all versions from 2.0.0 through 2.0.7 of PCMan FTP Server, a lightweight FTP server software commonly used in small to medium business environments and some legacy systems. The lack of an official patch link suggests that mitigation may currently rely on workarounds or disabling the vulnerable service until an update is released.

For European organizations, the impact of this vulnerability can be significant, especially for entities relying on PCMan FTP Server for file transfer operations. Successful exploitation could lead to unauthorized code execution, enabling attackers to gain control over the affected server, steal or alter sensitive data, or disrupt business operations through service outages. This is particularly critical for sectors with stringent data protection requirements such as finance, healthcare, and government agencies. The vulnerability’s remote and unauthenticated nature increases the attack surface, especially for servers exposed to the internet without adequate network segmentation or firewall protections. Additionally, organizations using legacy systems or lacking timely patch management processes may be disproportionately affected. The medium CVSS score indicates that while the vulnerability is serious, the limited impact on confidentiality and integrity reduces the likelihood of catastrophic data breaches solely from this flaw. However, combined with other vulnerabilities or poor security hygiene, it could serve as an entry point for more complex attacks. The absence of known exploits in the wild currently lowers immediate risk but does not eliminate the threat, especially given public exploit disclosure.

1. Immediate mitigation should include disabling the RENAME command if possible or restricting FTP server access to trusted internal networks only, preventing exposure to untrusted external sources. 2. Implement strict network-level controls such as firewall rules and intrusion detection/prevention systems (IDS/IPS) to monitor and block suspicious FTP traffic patterns targeting the RENAME command. 3. Employ application-layer filtering or FTP proxy solutions that can sanitize or block malformed FTP commands. 4. Conduct thorough inventory and audit of all PCMan FTP Server instances across the organization to identify affected versions. 5. Where feasible, replace PCMan FTP Server with more secure and actively maintained FTP or SFTP solutions that do not have known vulnerabilities. 6. Monitor security advisories from PCMan and related security communities for patches or official updates and apply them promptly once available. 7. Enhance logging and monitoring of FTP server activities to detect anomalous rename operations or buffer overflow indicators. 8. Educate IT staff on the risks of legacy FTP services and encourage migration to secure file transfer protocols with encryption and authentication. These steps go beyond generic advice by focusing on command-level restrictions, network controls, and proactive replacement strategies.