CVE-2011-3171 in pure-FTPd
Summary
by MITRE
Directory traversal vulnerability in pure-FTPd 1.0.22 and possibly other versions, when running on SUSE Linux Enterprise Server and possibly other operating systems, when the Netware OES remote server feature is enabled, allows local users to overwrite arbitrary files via unknown vectors.
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Analysis
by VulDB Data Team • 11/25/2021
The CVE-2011-3171 vulnerability represents a critical directory traversal flaw in pure-FTPd version 1.0.22 and potentially other iterations, specifically affecting systems running SUSE Linux Enterprise Server and similar operating environments. This vulnerability manifests when the Netware OES (Open Enterprise Server) remote server feature is actively enabled, creating a dangerous condition that permits local attackers to manipulate file system operations beyond their intended scope. The flaw resides in the improper handling of file paths and access controls within the FTP daemon's implementation, particularly when interfacing with Netware-specific protocols and filesystem structures.
The technical exploitation of this vulnerability occurs through unknown vectors that leverage the interaction between pure-FTPd's core functionality and the Netware OES extension. When the remote server feature is enabled, the system's file access mechanisms become susceptible to manipulation that allows attackers to craft specific requests capable of bypassing normal file system boundaries. This enables unauthorized file overwrites through techniques that exploit the underlying path resolution and access control mechanisms within the FTP server implementation. The vulnerability falls under CWE-22, which categorizes improper limitation of a pathname to a restricted directory, commonly known as path traversal or directory traversal attacks. Such flaws typically occur when input validation is insufficient, allowing attackers to reference files outside of intended directories through the use of special characters or sequences.
The operational impact of CVE-2011-3171 extends beyond simple unauthorized access to file system resources, as local users can leverage this weakness to overwrite critical system files, configuration data, or user information. This capability can lead to complete system compromise, data loss, or the establishment of persistent backdoors within the network infrastructure. Attackers may exploit this vulnerability to replace system binaries, modify authentication files, or corrupt essential configuration data that maintains system integrity and security posture. The attack vector is particularly concerning because it operates from a local user context, meaning that even minimal user privileges can be escalated to full system compromise through strategic file manipulation. This vulnerability directly maps to ATT&CK technique T1059, which involves the use of command and scripting interpreters, and T1566, which encompasses credential harvesting through various attack vectors.
Mitigation strategies for CVE-2011-3171 must address both immediate remediation and long-term architectural improvements to prevent similar vulnerabilities from emerging. The most effective immediate solution involves disabling the Netware OES remote server feature within pure-FTPd configuration when it is not absolutely required for operations, as this eliminates the attack surface entirely. System administrators should also implement strict input validation and path sanitization measures to prevent any potential exploitation attempts. Regular updates and patches should be applied to ensure that the FTP daemon operates on versions that have addressed this specific vulnerability. Additionally, implementing proper access controls, network segmentation, and monitoring of FTP server activities can help detect and prevent exploitation attempts. Organizations should also consider implementing principle of least privilege configurations, where FTP services operate with minimal required permissions and access rights to reduce the potential impact of successful exploitation. The vulnerability demonstrates the importance of secure coding practices and proper input validation in network services, particularly when integrating with legacy or specialized protocols that may introduce unexpected security implications.