CVE-2017-15269 in PSFTPd
Summary
by MITRE
The PSFTPd 10.0.4 Build 729 server does not prevent FTP bounce scans by default. These can be performed using "nmap -b" and allow performing scans via the FTP server.
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Analysis
by VulDB Data Team • 01/10/2023
The vulnerability identified as CVE-2017-15269 affects the PSFTPd 10.0.4 Build 729 FTP server implementation, presenting a significant security weakness that enables unauthorized network reconnaissance activities. This flaw stems from the server's failure to properly implement bounce attack prevention mechanisms, which are essential controls for maintaining network security boundaries. The vulnerability specifically impacts the server's handling of FTP bounce scan requests, allowing malicious actors to exploit this weakness for network reconnaissance purposes.
The technical flaw manifests through the server's inadequate enforcement of FTP protocol restrictions that should prevent bounce attacks. In standard FTP implementations, bounce attacks occur when an attacker uses the FTP server as a proxy to conduct port scans against other network hosts. The PSFTPd server fails to properly validate or restrict these operations, enabling attackers to leverage the "nmap -b" command to perform stealthy network scanning through the vulnerable FTP server. This occurs because the server does not properly implement the required safeguards that would normally block or restrict the use of the FTP STOR and RETR commands for scanning purposes, which are fundamental to preventing such attacks.
The operational impact of this vulnerability extends beyond simple network reconnaissance, creating potential pathways for more sophisticated attacks and compromising the overall security posture of systems relying on the vulnerable FTP server. Attackers can utilize this weakness to map network topology, identify open ports, and discover potentially vulnerable systems without directly connecting to them, effectively using the FTP server as an intermediary for reconnaissance activities. This capability significantly reduces the attacker's ability to remain undetected while gathering intelligence about target networks, making it particularly dangerous in environments where network monitoring and detection systems may not immediately flag such indirect scanning techniques.
The vulnerability aligns with CWE-642, which addresses weaknesses in the design of security mechanisms that allow indirect access to resources, and can be categorized under ATT&CK technique T1046 for network service scanning. Organizations utilizing this FTP server implementation face increased risk of reconnaissance activities that could lead to further exploitation attempts, as attackers can leverage the bounce scanning capability to identify additional attack vectors. The lack of proper bounce attack prevention mechanisms creates a persistent security gap that remains unaddressed without specific configuration changes or software updates. Security professionals should consider this vulnerability as part of broader network security assessments, particularly when evaluating the effectiveness of perimeter defense mechanisms and the overall security posture of file transfer services within their environments.
Mitigation strategies for this vulnerability require immediate attention through software updates to the PSFTPd server, ensuring that bounce attack prevention mechanisms are properly enabled and configured. Organizations should also implement network-level controls including firewall rules that restrict FTP protocol usage and prevent unauthorized scanning activities. Additionally, network monitoring should be enhanced to detect unusual FTP traffic patterns that may indicate bounce attack attempts, while regular security assessments should verify that FTP server configurations properly enforce security policies. The implementation of these controls addresses the core technical flaw by ensuring that the server properly enforces FTP protocol restrictions and prevents unauthorized proxy-based scanning activities.