CVE-2025-3373: Pcman FTP Server Buffer Overflow Flaw

CVE-2025-3373 Overview

A critical buffer overflow vulnerability has been identified in PCMan FTP Server version 2.0.7. The vulnerability exists within the SITE CHMOD Command Handler component, where improper bounds checking allows remote attackers to overflow memory buffers. This flaw can be exploited remotely without authentication, potentially leading to arbitrary code execution, denial of service, or system compromise.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability in the SITE CHMOD command handler to potentially execute arbitrary code or crash the FTP server, affecting system availability and integrity.

Affected Products

• PCMan FTP Server 2.0.7
• pcman ftp_server (cpe:2.3:a:pcman:ftp_server:2.0.7:::::::*)

Discovery Timeline

• 2025-04-07 - CVE-2025-3373 published to NVD
• 2025-05-16 - Last updated in NVD database

Technical Details for CVE-2025-3373

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The SITE CHMOD command handler in PCMan FTP Server fails to properly validate the length of user-supplied input before copying it into a fixed-size buffer. When an attacker sends a specially crafted SITE CHMOD command with an excessively long argument, the application writes beyond the allocated buffer boundaries, corrupting adjacent memory regions.

The network-accessible nature of FTP services means this vulnerability can be exploited remotely by any attacker who can establish a connection to the FTP server. The exploit has been publicly disclosed, increasing the risk of exploitation in the wild.

Root Cause

The root cause of this vulnerability is insufficient input validation and boundary checking in the SITE CHMOD command processing routine. The application allocates a fixed-size buffer for handling CHMOD command parameters but does not verify that incoming data fits within this allocation before performing memory copy operations. This classic buffer overflow pattern allows attackers to overwrite stack or heap memory, depending on the specific implementation.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Establishing a connection to the vulnerable PCMan FTP Server
2. Sending a malformed SITE CHMOD command with an oversized argument
3. The oversized input overflows the internal buffer, potentially overwriting return addresses or function pointers
4. Depending on the attacker's payload, this can result in arbitrary code execution, denial of service, or information disclosure

The vulnerability is particularly dangerous because the SITE command is a standard FTP command that may be accessible even to anonymous users depending on server configuration.

Detection Methods for CVE-2025-3373

Indicators of Compromise

• Unusual FTP traffic patterns with abnormally large SITE CHMOD commands
• FTP server crashes or unexpected restarts without administrative action
• Memory access violations or segmentation faults in FTP server logs
• Network connections from unexpected sources to FTP service ports (typically port 21)

Detection Strategies

• Monitor FTP traffic for SITE CHMOD commands with arguments exceeding normal length thresholds (typically > 256 bytes)
• Deploy network intrusion detection signatures to identify buffer overflow attempts targeting FTP SITE commands
• Configure application-level logging to capture all SITE command executions with their parameters
• Implement anomaly detection for unusual FTP command sequences or connection patterns

Monitoring Recommendations

• Enable verbose logging on FTP servers to capture command execution details
• Monitor system resources for unexpected memory consumption or process crashes associated with the FTP service
• Set up alerts for FTP service restarts or failures
• Review firewall logs for scanning activity targeting FTP services

How to Mitigate CVE-2025-3373

Immediate Actions Required

• Disable or restrict access to the SITE CHMOD command if not required for business operations
• Implement network-level access controls to limit FTP server exposure to trusted networks only
• Consider replacing PCMan FTP Server with actively maintained FTP server software
• Deploy web application firewall (WAF) or intrusion prevention system (IPS) rules to filter malicious SITE CHMOD commands

Patch Information

No official vendor patch has been identified for this vulnerability. PCMan FTP Server appears to be legacy software with limited vendor support. Organizations using this software should consider migrating to alternative FTP server solutions that receive regular security updates.

For additional technical details and exploit information, refer to the VulDB entry #303619 and the Fitoxs Exploit Document.

Workarounds

• Disable the SITE command functionality entirely if supported by server configuration
• Implement strict firewall rules to allow FTP access only from known, trusted IP addresses
• Deploy a reverse proxy or application gateway that can inspect and sanitize FTP commands before reaching the server
• Consider migrating to a more secure, actively maintained FTP server such as FileZilla Server, vsftpd, or ProFTPD