CVE-2006-6240 in Telnet-FTP Server
Summary
by MITRE
Directory traversal vulnerability in Sorin Chitu Telnet-FTP Server 1.0 allows remote authenticated users to list contents of arbitrary directories and download arbitrary files via a .. (dot dot) sequence in an FTP command argument, as demonstrated by RETR (GET) or STOR (PUT). NOTE: The provenance of this information is unknown; the details are obtained solely from third party information.
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Analysis
by VulDB Data Team • 09/30/2017
This vulnerability represents a critical directory traversal flaw in the Sorin Chitu Telnet-FTP Server version 1.0 that enables authenticated remote attackers to bypass normal file access controls and gain unauthorized access to system resources. The vulnerability specifically affects the server's handling of FTP commands where users can manipulate directory paths through the use of dot-dot sequences in command arguments. The flaw exists in the server's input validation mechanisms that fail to properly sanitize or restrict directory traversal sequences, allowing malicious users to navigate outside the intended directory structure and access files they should not be permitted to reach.
The technical implementation of this vulnerability occurs when the FTP server processes commands such as RETR (GET) or STOR (PUT) with arguments containing .. sequences that should be rejected or properly normalized. When an authenticated user submits a command with directory traversal elements, the server fails to adequately validate the input path, allowing the attacker to specify arbitrary file paths that can be resolved relative to the server's root directory. This creates a path traversal condition where the server's file system access controls are effectively bypassed, enabling enumeration of directory contents and retrieval of files that would normally be protected from unauthorized access. The vulnerability operates at the application layer and specifically targets the FTP protocol implementation within the server software.
The operational impact of this vulnerability is significant as it allows attackers who have already established authentication credentials to escalate their privileges and access sensitive system information. Remote authenticated users can list directory contents of arbitrary locations on the server, potentially discovering system configuration files, user data, or other sensitive resources. The ability to download arbitrary files means that attackers can retrieve confidential information, system binaries, or other valuable data from the server's file system. This vulnerability essentially transforms a limited authenticated access point into a full system reconnaissance and data exfiltration capability, making it particularly dangerous for environments where the server hosts sensitive information or serves as a gateway to other systems.
The 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. This weakness is classified under the broader category of input validation flaws that occur when applications fail to properly sanitize user-supplied input before using it in file system operations. From an attack framework perspective, this vulnerability maps to multiple ATT&CK techniques including T1083 for discovering files and directories, T1074 for data staging, and T1566 for credential access through exploitation of weak authentication controls. The attack chain typically begins with authentication to the FTP server, followed by the execution of directory traversal commands that leverage the server's insufficient input validation to gain access to unintended file system locations.
Mitigation strategies for this vulnerability should include immediate patching of the affected Telnet-FTP server software to address the input validation flaw in the directory traversal handling. Organizations should implement strict input validation and sanitization for all file system operations, particularly those involving user-supplied paths in FTP commands. The server configuration should enforce proper path normalization and reject any input containing directory traversal sequences such as .. or %2e%2e. Network segmentation and access controls should be implemented to limit the exposure of FTP services to only authorized users, while also implementing monitoring and logging of FTP commands to detect suspicious activity. Regular security assessments should include vulnerability scanning for similar path traversal issues in other network services, and system administrators should maintain updated security patches for all server software components to prevent exploitation of known vulnerabilities.