CVE-2003-0343 in BlackMoon FTP Server
Summary
by MITRE
BlackMoon FTP Server 2.6 Free Edition, and possibly other distributions and versions, generates an "Account does not exist" error message when an invalid username is entered, which makes it easier for remote attackers to conduct brute force attacks.
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Analysis
by VulDB Data Team • 05/11/2019
The vulnerability identified as CVE-2003-0343 affects the BlackMoon FTP Server version 2.6 Free Edition and potentially other distributions, presenting a significant security weakness in authentication handling mechanisms. This flaw manifests through the server's response behavior during failed authentication attempts, where it provides a specific error message indicating that the account does not exist rather than implementing a generic failure response. The vulnerability resides in the server's design philosophy and implementation approach to user authentication, creating a predictable pattern that adversaries can exploit systematically.
The technical flaw stems from the server's implementation of account validation during the authentication process. When an attacker submits an invalid username, the system responds with a specific error message that explicitly states "Account does not exist" rather than returning a generic authentication failure. This behavior directly violates fundamental security principles that require authentication systems to provide consistent responses regardless of whether the username exists. The predictable nature of this response creates a reconnaissance opportunity for attackers, as they can determine the existence of valid accounts through simple trial and error attempts.
This vulnerability significantly impacts operational security by enabling brute force attacks against the FTP server. Attackers can systematically test username and password combinations, using the specific error message as feedback to identify valid accounts within the system. The vulnerability essentially provides a credential enumeration mechanism that bypasses normal security controls, allowing unauthorized access to the server's file system and potentially sensitive data stored within. The impact extends beyond simple unauthorized access, as successful exploitation can lead to complete system compromise and data breaches.
The security implications of this vulnerability align with CWE-305 authentication weakness categories and map to attack techniques described in the MITRE ATT&CK framework under credential access and brute force methods. The predictable error response creates an information disclosure vulnerability that exposes account existence information, which can be leveraged in conjunction with password spraying or dictionary attacks to gain unauthorized system access. Organizations using this FTP server version face heightened risk during security assessments and penetration testing, as this vulnerability can be exploited without sophisticated techniques.
Mitigation strategies should focus on implementing consistent error responses regardless of account validity, ensuring that all authentication attempts return identical failure messages to prevent account enumeration. The server should be updated to the latest version that addresses this specific vulnerability, as the original BlackMoon FTP Server 2.6 Free Edition has been superseded by more secure implementations. Network-level protections including firewall rules, rate limiting, and intrusion detection systems can provide additional defense in depth. Organizations should also implement account lockout mechanisms and multi-factor authentication where possible, while conducting regular security audits to identify similar vulnerabilities in other services and applications. The vulnerability demonstrates the critical importance of proper error handling in security-sensitive applications and the necessity of following security best practices during system development and deployment phases.