CVE-2006-2173 in Filezilla Server
Summary
by MITRE
Buffer overflow in FileZilla FTP Server 2.2.22 allows remote authenticated attackers to cause a denial of service and possibly execute arbitrary code via a long (1) PORT or (2) PASS followed by the MLSD command, or (2) the remote server interface, as demonstrated by the Infigo FTPStress Fuzzer.
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Analysis
by VulDB Data Team • 06/22/2025
The vulnerability identified as CVE-2006-2173 represents a critical buffer overflow flaw in FileZilla FTP Server version 2.2.22 that exposes remote authenticated attackers to significant operational risks. This vulnerability specifically targets the server's handling of FTP commands and demonstrates how improper input validation can lead to system compromise. The flaw manifests when the server processes certain sequences of commands, particularly involving the PORT and PASS commands followed by MLSD or through the remote server interface. The attack vector requires authentication, meaning that only legitimate users with valid credentials can exploit this vulnerability, though this does not mitigate the severity of potential impact.
The technical implementation of this buffer overflow occurs during command processing within the FTP server's core functionality. When an authenticated user sends a specially crafted sequence of commands including a long PORT or PASS parameter followed by MLSD, the server fails to properly validate the input length before copying data into fixed-size buffers. This classic buffer overflow condition allows attackers to overwrite adjacent memory locations, potentially corrupting program execution flow and enabling arbitrary code execution. The vulnerability aligns with CWE-121, which describes buffer overflow conditions where insufficient bounds checking allows data to be written beyond allocated buffer boundaries. The attack mechanism leverages the FTP protocol's command structure to manipulate server memory, making it particularly dangerous in networked environments where FTP servers handle multiple concurrent connections.
The operational impact of this vulnerability extends beyond simple denial of service to encompass potential system compromise and unauthorized code execution. An attacker who successfully exploits this vulnerability could gain control over the FTP server, potentially accessing sensitive files, modifying server configurations, or using the compromised system as a launching point for further attacks within the network. The demonstration using Infigo FTPStress Fuzzer confirms the exploitability of this vulnerability in real-world scenarios, showing that automated testing tools can readily identify and exploit this weakness. This vulnerability affects organizations that rely on FileZilla FTP Server for file transfer operations, particularly those with less stringent security monitoring and patch management processes.
Mitigation strategies for CVE-2006-2173 require immediate action including patching the FileZilla FTP Server to version 2.2.23 or later, which contains the necessary code fixes to prevent buffer overflow conditions. Organizations should also implement network segmentation to limit access to FTP servers, enforce strict authentication mechanisms, and monitor FTP server logs for suspicious command sequences. The ATT&CK framework categorizes this vulnerability under T1071.001 for application layer protocol usage and T1059.001 for command and scripting interpreter, highlighting how attackers might use this vulnerability to establish persistent access. Additional defensive measures include implementing intrusion detection systems that can identify unusual FTP command patterns and configuring firewalls to restrict FTP traffic to necessary network segments only. Regular security assessments and vulnerability scanning should be conducted to identify similar weaknesses in other network services and applications.