CVE-2004-0243 in AIX
Summary
by MITRE
AIX 4.3.3 through AIX 5.1, when direct remote login is disabled, displays a different message if the password is correct, which allows remote attackers to guess the password via brute force methods.
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Analysis
by VulDB Data Team • 04/13/2019
This vulnerability exists in IBM AIX operating systems versions 4.3.3 through 5.1 where the authentication mechanism exhibits inconsistent error messaging behavior. When direct remote login is disabled, the system provides different response messages depending on whether the username exists or whether the password is correct, creating a timing and response discrepancy that can be exploited by attackers. The flaw stems from the authentication subsystem's failure to maintain consistent response behavior regardless of the validation outcome, which violates fundamental security principles of uniform error handling. This vulnerability directly relates to CWE-204, which addresses information exposure through inconsistent error messages, and represents a classic example of how seemingly minor implementation details can create significant security weaknesses. The inconsistency in response messages provides attackers with valuable information that would otherwise remain hidden, enabling them to perform targeted brute force attacks with higher success rates.
The technical implementation of this vulnerability occurs at the authentication service level where the system's response to authentication attempts is not uniformly handled. When an attacker attempts to authenticate with a non-existent username, the system provides one response pattern, but when attempting to authenticate with an existing username and incorrect password, it provides a different response pattern. This differential response behavior allows an attacker to distinguish between valid and invalid usernames through careful analysis of the system's responses, effectively creating a user enumeration mechanism. The vulnerability operates within the context of remote authentication protocols and demonstrates a failure in applying the principle of least information disclosure. According to ATT&CK framework, this represents a technique for credential access through brute force methods, specifically leveraging information leakage to improve attack efficiency. The timing differences in response handling create a side-channel attack vector that can be exploited by automated tools to systematically determine valid accounts and passwords.
The operational impact of this vulnerability extends beyond simple credential theft, as it fundamentally undermines the security of the authentication system and provides attackers with a pathway to systematically compromise multiple accounts. An attacker can use this information to reduce the search space for brute force attacks significantly, as they can first identify valid usernames before focusing their efforts on password guessing. This vulnerability is particularly dangerous in environments where multiple users exist and where password reuse patterns may be present, as successful exploitation can lead to lateral movement and privilege escalation. The impact is amplified by the fact that this vulnerability affects multiple versions of AIX, creating a widespread exposure across various system configurations. Organizations with remote access capabilities and insufficient monitoring of authentication attempts may experience unauthorized access without detection, as the system's inconsistent behavior masks the actual attack patterns. This vulnerability also affects the system's ability to provide reliable authentication logging and audit trails, as the timing and response variations make it difficult to establish accurate baseline behaviors for legitimate authentication attempts.
Mitigation strategies for this vulnerability require immediate implementation of consistent error messaging across all authentication attempts, ensuring that the system provides identical response patterns regardless of whether the username exists or whether the password is correct. Organizations should implement account lockout mechanisms and rate limiting to prevent automated brute force attacks, while also deploying monitoring solutions that can detect unusual authentication patterns and potential exploitation attempts. The system configuration should be reviewed to ensure that direct remote login is properly restricted and that additional authentication layers such as two-factor authentication are implemented. Network segmentation and access controls should be enhanced to limit the attack surface, and regular security audits should be conducted to verify that authentication systems maintain consistent behavior. From a compliance perspective, this vulnerability affects systems that must meet standards such as iso 27001 and pci dss, which require robust authentication controls and protection against credential guessing attacks. Regular patch management and security updates should be implemented to address similar issues in other system components, and security awareness training should be provided to administrators regarding the importance of consistent error handling in authentication systems.