CVE-2000-0640 in Guild FTPD
Summary
by MITRE
Guild FTPd allows remote attackers to determine the existence of files outside the FTP root via a .. (dot dot) attack, which provides different error messages depending on whether the file exists or not.
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Analysis
by VulDB Data Team • 10/13/2025
The vulnerability identified as CVE-2000-0640 affects Guild FTPd, a file transfer protocol server implementation that suffers from a directory traversal flaw. This weakness enables remote attackers to perform dot dot attacks by manipulating directory paths to access files outside the designated FTP root directory. The vulnerability stems from inadequate input validation and path resolution mechanisms within the FTP server's handling of relative path references. When an attacker constructs a request using double dot sequences followed by forward slashes, the server fails to properly sanitize these path components, allowing unauthorized access to the file system beyond the intended boundaries.
The technical implementation of this vulnerability operates through the exploitation of insufficient path normalization and validation routines. When a user requests a file using a path containing .. sequences, the FTP server does not adequately resolve these references to prevent traversal outside the designated root directory. This flaw manifests in different error responses depending on whether the target file exists or not, providing attackers with information disclosure about the underlying file system structure. The server's response behavior creates a reconnaissance opportunity for attackers to map directory structures and identify sensitive files without proper authentication or authorization.
The operational impact of this vulnerability extends beyond simple information disclosure, as it fundamentally compromises the security boundary of the FTP server. Attackers can leverage this weakness to access system files, configuration data, and potentially sensitive user information that should remain isolated within the FTP root directory. The vulnerability enables a form of passive reconnaissance that can reveal system architecture details, file naming conventions, and directory structures that would normally be protected by proper access controls. This information can serve as a foundation for more sophisticated attacks against the system or network infrastructure.
From a cybersecurity perspective, this vulnerability aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. The flaw represents a classic example of insufficient input validation and inadequate privilege separation between the FTP service and the underlying file system. The vulnerability also maps to ATT&CK technique T1083, which covers directory and file system discovery, as the attacker can systematically enumerate file system contents through the error message differences. Organizations using Guild FTPd are particularly vulnerable as this represents a fundamental architectural weakness that can be exploited without requiring elevated privileges or specialized tools.
Mitigation strategies for CVE-2000-0640 should focus on implementing proper path validation and normalization mechanisms within the FTP server implementation. The most effective approach involves ensuring that all path components are properly resolved and validated against the designated root directory before any file operations are performed. This includes implementing strict input sanitization that removes or rejects any sequences that could potentially lead to directory traversal. Additionally, system administrators should consider implementing network-level restrictions such as firewall rules to limit access to FTP services and ensure that only authorized users can connect. Regular security audits and vulnerability assessments should be conducted to identify similar weaknesses in other services and applications. The most comprehensive solution involves upgrading to a modern FTP server implementation that properly handles path resolution and implements robust access control mechanisms to prevent unauthorized file system access.