CVE-2004-2487 in FTP Server
Summary
by MITRE
Directory traversal vulnerability in Nexgen FTP Server before 2.2.3.23 allows remote authenticated users to read or list arbitrary files via (1) "..", (2) "\..\" (backslash dot dot), or (3) "/../" sequences in (a) RETR (get), (b) NLST (ls), (c) LIST (ls), (d) RNFR, or (e) RNTO FTP commands.
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Analysis
by VulDB Data Team • 09/30/2025
The vulnerability described in CVE-2004-2487 represents a critical directory traversal flaw in the Nexgen FTP Server software, specifically affecting versions prior to 2.2.3.23. This security weakness allows authenticated remote attackers to bypass normal file access controls and gain unauthorized access to arbitrary files on the server filesystem. The vulnerability stems from insufficient input validation and path resolution mechanisms within the FTP server implementation, creating a pathway for malicious users to navigate beyond the intended directory boundaries. The flaw specifically impacts several core FTP commands including RETR for file retrieval, NLST and LIST for directory listing, and RNFR/RNTO for file renaming operations, making it particularly dangerous as it can be exploited across multiple file operations. The vulnerability's exploitation requires only authentication credentials, meaning that any legitimate user with access to the FTP server can potentially leverage this flaw to access files they should not be authorized to view.
The technical implementation of this directory traversal vulnerability occurs through the manipulation of path sequences that are commonly used to navigate up directory levels in file systems. Attackers can exploit this by using three specific patterns: the standard dot-dot-slash sequence "..", the backslash variant "\..\", and the forward slash variant "/../". These sequences, when included in FTP commands such as RETR, NLST, LIST, RNFR, or RNTO, cause the server to interpret the file paths incorrectly and traverse to parent directories. The underlying issue lies in how the FTP server processes these path sequences without proper sanitization or validation, allowing the traversal to occur. This type of vulnerability is classified as CWE-22 - Improper Limitation of a Pathname to a Restricted Directory, which is a well-documented weakness in software security where input validation fails to properly restrict file access to authorized directories. The vulnerability demonstrates a classic case of insufficient input filtering and path traversal protection mechanisms.
The operational impact of this vulnerability extends beyond simple unauthorized file access, as it can lead to complete system compromise and data exfiltration. An authenticated attacker with access to the FTP server can potentially access sensitive configuration files, user credentials, application source code, and other critical system files that may contain sensitive information. The vulnerability affects multiple FTP operations, providing attackers with flexibility in how they approach the exploitation process and making detection more difficult. The ability to use different path traversal sequences also means that standard security controls that might block one pattern may not prevent exploitation through alternative methods. This vulnerability can be particularly damaging in enterprise environments where FTP servers often contain business-critical data and where attackers may use this access to escalate privileges or gain additional system access. The fact that this vulnerability affects file listing operations means that attackers can also enumerate directory structures and identify additional targets for exploitation. From an operational security standpoint, this vulnerability represents a significant risk to organizations that rely on FTP servers for file transfers and may not have adequate monitoring or intrusion detection systems in place to detect such attacks.
The mitigation strategies for this vulnerability should focus on immediate patching of the affected Nexgen FTP Server software to version 2.2.3.23 or later, which contains the necessary security fixes. Organizations should also implement additional controls such as restricting FTP access to trusted networks, implementing proper access controls and user permissions, and monitoring FTP server logs for suspicious activity including unusual path traversal attempts. Network segmentation and firewall rules should be configured to limit access to FTP services to only authorized users and systems. From a defensive perspective, implementing proper input validation and sanitization for all file path operations can help prevent similar vulnerabilities in other applications. This vulnerability aligns with several ATT&CK techniques including T1078 - Valid Accounts for maintaining persistence and T1566 - Phishing for initial access, as well as T1005 - Data from Local System for accessing sensitive files. Organizations should also consider implementing automated vulnerability scanning and penetration testing to identify similar path traversal vulnerabilities in other systems and applications. The vulnerability demonstrates the importance of proper security testing and input validation in network services, particularly those handling file operations and user-provided paths. Regular security audits and updates of all network services are essential to prevent exploitation of known vulnerabilities like this one that can be easily remediated through proper patch management procedures.