CVE-2006-6564 in Server
Summary
by MITRE
FileZilla Server before 0.9.22 allows remote attackers to cause a denial of service (crash) via a malformed argument to the STOR command, which results in a NULL pointer dereference. NOTE: CVE analysis suggests that the problem might be due to a malformed PORT command.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 07/12/2019
The vulnerability identified as CVE-2006-6564 affects FileZilla Server versions prior to 0.9.22 and represents a critical denial of service flaw that can be exploited by remote attackers to crash the server application. This vulnerability manifests when the server receives a malformed argument to the STOR command, which is part of the File Transfer Protocol (FTP) standard used for transferring files between computers. The flaw results in a NULL pointer dereference condition that causes the server process to terminate unexpectedly, effectively denying legitimate users access to the file sharing services.
The technical implementation of this vulnerability stems from inadequate input validation within the FileZilla Server's command processing logic. When a client sends a STOR command with malformed parameters, the server fails to properly validate the input before attempting to process it, leading to a situation where a null pointer is dereferenced during the file upload operation. This type of vulnerability falls under the category of improper input validation as classified by CWE-20, which is a fundamental weakness in software design that allows malicious inputs to trigger unexpected behavior in applications. The vulnerability can be exploited through the FTP protocol's data connection handling mechanisms, where the server's response to malformed commands creates a memory access violation that terminates the service.
From an operational perspective, this vulnerability presents a significant risk to organizations relying on FileZilla Server for file sharing operations. The denial of service impact means that legitimate users cannot access file transfer services during an attack, potentially disrupting business operations and causing productivity losses. The remote exploitation capability means that attackers do not need physical access to the system or network to trigger the vulnerability, making it particularly dangerous in networked environments. Attackers can simply connect to the FTP server and send a specially crafted STOR command with malformed arguments to cause the server to crash, requiring manual intervention to restart the service and restore normal operations.
The vulnerability's potential for broader impact extends beyond simple service disruption, as it can be leveraged as part of larger attack campaigns targeting FTP servers in enterprise environments. The flaw demonstrates a classic software security weakness where error handling mechanisms fail to account for malformed input, creating a path for attackers to destabilize critical infrastructure services. Organizations using FileZilla Server should consider implementing network-level mitigations such as firewall rules that restrict FTP access to trusted networks, though the most effective solution involves upgrading to FileZilla Server version 0.9.22 or later where the vulnerability has been patched. The patch addresses the input validation issue by properly sanitizing command arguments before processing them, preventing the NULL pointer dereference condition that previously caused crashes.
This vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, and represents a common pattern in FTP server implementations where protocol parsing lacks proper boundary checking. The issue highlights the importance of robust input validation in network services and demonstrates how seemingly simple protocol commands can become attack vectors when proper error handling is absent. The vulnerability serves as a reminder of the critical need for thorough security testing of network protocols and the importance of maintaining up-to-date software versions to protect against known exploits. Organizations should also implement monitoring solutions to detect unusual patterns of FTP server crashes that might indicate exploitation attempts, as the service disruption can serve as an indicator of active attacks targeting FTP infrastructure.