CVE-2001-0054 in Serv-U
Summary
by MITRE
Directory traversal vulnerability in FTP Serv-U before 2.5i allows remote attackers to escape the FTP root and read arbitrary files by appending a string such as "/..%20." to a CD command, a variant of a .. (dot dot) attack.
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Analysis
by VulDB Data Team • 03/06/2025
The vulnerability described in CVE-2001-0054 represents a critical directory traversal flaw in FTP Serv-U software versions prior to 2.5i, which exposes systems to unauthorized file access and potential data breaches. This weakness stems from inadequate input validation within the File Transfer Protocol implementation, specifically affecting the CD command functionality that handles directory navigation. Attackers can exploit this vulnerability by crafting malicious requests that append sequences such as "/..%20." to the CD command, effectively bypassing the intended file system boundaries and gaining access to files outside the designated FTP root directory.
The technical nature of this vulnerability aligns with CWE-22, which categorizes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. This flaw operates by manipulating the path resolution mechanism within the FTP server to navigate upward through directory structures, allowing attackers to access files that should remain restricted. The exploitation technique leverages URL encoding where %20 represents a space character, making the attack more stealthy and potentially bypassing basic security filters that might not properly decode such sequences. The vulnerability specifically targets the FTP Serv-U software's handling of relative path references, demonstrating a fundamental failure in input sanitization and access control enforcement.
The operational impact of this vulnerability extends beyond simple unauthorized file access, as it can enable attackers to read sensitive system files, configuration data, and potentially execute arbitrary code if combined with other exploitation techniques. In enterprise environments, this vulnerability could compromise the integrity of file transfer operations and expose confidential data stored on the affected servers. The remote nature of the attack means that adversaries do not require physical access or local privileges to exploit the vulnerability, making it particularly dangerous for publicly accessible FTP services. Organizations using vulnerable versions of FTP Serv-U face significant risks including data exfiltration, system compromise, and potential violations of data protection regulations due to unauthorized access to protected information.
Mitigation strategies for CVE-2001-0054 primarily involve immediate patching of the FTP Serv-U software to version 2.5i or later, which contains the necessary security fixes to prevent directory traversal attacks. System administrators should also implement additional security measures including restricting FTP access to trusted networks, implementing proper input validation at all levels of the application stack, and configuring access controls that limit user privileges within the file system. Network segmentation and firewall rules can help reduce the attack surface by limiting access to FTP services from untrusted sources. The vulnerability also highlights the importance of following security best practices such as the principle of least privilege and regular security assessments to identify and remediate similar weaknesses in other applications and services. Organizations should also consider implementing intrusion detection systems that can monitor for suspicious FTP command sequences and alert administrators to potential exploitation attempts. This vulnerability serves as a reminder of the critical importance of proper input validation and access control mechanisms in network services, particularly those handling file system operations and user requests that could potentially manipulate directory paths.