CVE-2007-6739 in pyftpdlib
Summary
by MITRE
FTPServer.py in pyftpdlib before 0.2.0 allows remote attackers to cause a denial of service via a long command.
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Analysis
by VulDB Data Team • 02/07/2019
The vulnerability identified as CVE-2007-6739 affects the pyftpdlib FTP server implementation, specifically the FTPServer.py component in versions prior to 0.2.0. This issue represents a classic denial of service vulnerability that exploits improper input validation mechanisms within the FTP protocol handling code. The flaw manifests when remote attackers send excessively long command sequences to the FTP server, causing the application to crash or become unresponsive. The vulnerability stems from inadequate buffer management and command parsing logic that fails to properly handle command length limitations, creating a condition where the server cannot process the malformed input gracefully.
The technical implementation of this vulnerability resides in the command processing loop of the FTP server where incoming commands are read and parsed without sufficient length validation. When a command exceeds the expected buffer size or predefined length limits, the server's parsing routine encounters a memory management issue that results in a crash or resource exhaustion. This behavior aligns with CWE-122, which describes buffer overflow conditions that occur when insufficient bounds checking is performed on buffer operations. The vulnerability operates at the application layer of the network stack, specifically targeting the FTP protocol implementation within the pyftpdlib library, making it accessible to any attacker with network connectivity to the affected server.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable more sophisticated attack vectors. An attacker can exploit this weakness to repeatedly send long command sequences, causing sustained denial of service against legitimate users who require FTP access for file transfers and server management. The vulnerability affects any system running pyftpdlib versions before 0.2.0, including development environments, production servers, and testing infrastructure that relies on this Python-based FTP implementation. Organizations using this library for FTP services face significant risk of service availability compromise, particularly in environments where FTP access is critical for business operations or data exchange processes.
Mitigation strategies for CVE-2007-6739 primarily involve upgrading to pyftpdlib version 0.2.0 or later, which contains the necessary patches to address the command length validation issues. System administrators should also implement network-level protections such as firewall rules that limit the size of incoming FTP commands or implement rate limiting to prevent abuse of the vulnerability. Additionally, monitoring and logging mechanisms should be enhanced to detect unusual command length patterns that may indicate attempted exploitation. Organizations should consider implementing intrusion detection systems that can identify and alert on malformed FTP command sequences. The vulnerability demonstrates the importance of proper input validation and buffer management practices, aligning with ATT&CK technique T1499.004 which covers network denial of service attacks and emphasizes the need for robust application-level defenses against malformed input processing.