CVE-2005-4673 in ioFTPD
Summary
by MITRE
ioFTPD 0.5.84 u responds with different messages depending on whether or not a username exists, which allows remote attackers to enumerate valid usernames.
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Analysis
by VulDB Data Team • 07/16/2018
The vulnerability identified as CVE-2005-4673 affects ioFTPD version 0.5.84u and represents a classic username enumeration flaw that exposes fundamental security weaknesses in authentication mechanisms. This issue arises from the software's inconsistent response behavior when processing user authentication requests, creating a predictable pattern that adversaries can exploit to determine valid usernames within the system. The vulnerability specifically manifests when the ftpd service processes login attempts, where it provides different error messages or response codes depending on whether the attempted username exists in the system's user database. This differential response behavior creates a side-channel attack vector that bypasses traditional security controls and directly compromises the confidentiality of user account information.
The technical implementation of this vulnerability stems from poor input validation and response handling within the authentication subsystem of ioFTPD. When an attacker sends a login request with a username that does not exist, the server typically responds with one message format, whereas valid usernames trigger a different response pattern. This inconsistency in error messaging violates fundamental security principles that require uniform responses to prevent information leakage. The vulnerability operates at the application layer and can be classified under CWE-200, which specifically addresses "Information Exposure Through Output Values" and aligns with ATT&CK technique T1087.2.1, "Account Discovery: Local Account" as it enables adversaries to gather information about valid accounts through indirect means. The flaw demonstrates inadequate security design where the system's response behavior inadvertently reveals sensitive information about its internal state.
The operational impact of CVE-2005-4673 extends beyond simple username enumeration, creating a foundation for more sophisticated attacks that can lead to full system compromise. Once adversaries have identified valid usernames, they can proceed with targeted brute force attacks, credential stuffing, or social engineering campaigns that leverage the discovered account information. The vulnerability also enables reconnaissance activities that can be combined with other reconnaissance techniques to map the complete user landscape of the system. In environments where ioFTPD serves as a primary file transfer service, this weakness can provide attackers with a foothold for lateral movement and privilege escalation. The impact is particularly severe in scenarios where the ftpd service is exposed to untrusted networks, as the vulnerability can be exploited remotely without requiring prior access to the system. This makes the vulnerability especially dangerous in public-facing services or when the software is improperly configured within network perimeters.
Mitigation strategies for CVE-2005-4673 require both immediate configuration changes and long-term architectural improvements to address the root cause of the vulnerability. The most effective immediate solution involves configuring the ftpd service to provide consistent error responses regardless of whether a username exists, ensuring that all authentication attempts receive identical messaging patterns. This approach aligns with security best practices outlined in the OWASP Top Ten and follows the principle of least information disclosure. System administrators should also implement account lockout mechanisms and rate limiting to prevent automated enumeration attempts, while applying the latest available patches from the software vendor if available. Network-level protections including firewall rules and intrusion detection systems can help detect and block suspicious authentication patterns. Additionally, organizations should conduct regular security assessments to identify similar vulnerabilities in other authentication systems and implement comprehensive monitoring for unauthorized access attempts. The remediation process must also include user education regarding the importance of strong passwords and multi-factor authentication to reduce the overall risk surface when enumeration attacks are successful.