CVE-2025-4158 is a buffer overflow vulnerability identified in PCMan FTP Server versions up to and including 2.0.7. The flaw exists within the PROMPT Command Handler component of the server software. Buffer overflow vulnerabilities occur when a program writes more data to a buffer than it can hold, potentially overwriting adjacent memory. In this case, the vulnerability can be triggered remotely without requiring authentication or user interaction, as indicated by the CVSS vector (AV:N/AC:L/PR:N/UI:N). The attacker can send specially crafted commands to the FTP server, causing the buffer overflow condition. This may lead to arbitrary code execution, denial of service, or system compromise depending on how the overflow is exploited. The vulnerability has a CVSS 4.0 base score of 6.9, categorized as medium severity, reflecting a moderate impact on confidentiality, integrity, and availability with relatively low complexity of exploitation. No patches or fixes have been linked yet, and no known exploits are currently observed in the wild. However, the public disclosure of the vulnerability increases the risk of exploitation attempts. PCMan FTP Server is a lightweight FTP server solution used primarily on Windows platforms, often in small to medium business environments or by individual users for file transfer services. The PROMPT command is part of the FTP command set, and improper handling here suggests a coding flaw in input validation or buffer size management within the server's command parser.

For European organizations using PCMan FTP Server, this vulnerability poses a risk of remote compromise without authentication, potentially allowing attackers to execute arbitrary code or disrupt service availability. This could lead to unauthorized data access, data corruption, or service outages impacting business operations. Organizations relying on FTP servers for file transfers, especially those handling sensitive or regulated data, may face confidentiality breaches or integrity violations. The medium CVSS score suggests that while exploitation is feasible, the impact may be limited by the scope of affected systems and the specific deployment context. However, given the public disclosure, opportunistic attackers may target unpatched servers, increasing the likelihood of incidents. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate it. European entities in sectors such as manufacturing, SMBs, or public institutions that use PCMan FTP Server could be vulnerable, particularly if they have not implemented compensating controls or alternative secure file transfer mechanisms.

1. Immediate mitigation should include disabling the PROMPT command functionality if configurable or restricting access to the FTP server from untrusted networks via firewall rules or network segmentation. 2. Monitor network traffic for anomalous FTP commands or unexpected usage patterns indicative of exploitation attempts. 3. Employ intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics targeting buffer overflow attempts against FTP servers. 4. Where possible, replace PCMan FTP Server with more secure and actively maintained FTP or SFTP solutions that have robust input validation and security features. 5. Implement strict access controls and logging on FTP servers to detect and respond to suspicious activities promptly. 6. Regularly audit and inventory FTP server deployments across the organization to identify and remediate vulnerable versions. 7. Stay alert for official patches or updates from the vendor and apply them promptly once available. 8. Consider deploying application-layer firewalls or FTP proxies that can sanitize or block malformed commands targeting the PROMPT handler.