CVE-2000-0356 in Linux
Summary
by MITRE
Pluggable Authentication Modules (PAM) in Red Hat Linux 6.1 does not properly lock access to disabled NIS accounts.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-2000-0356 represents a critical authentication flaw within the Pluggable Authentication Modules framework of Red Hat Linux 6.1 systems. This issue specifically affects the handling of Network Information Service (NIS) accounts that have been disabled within the system. The flaw exists at the intersection of authentication management and account control mechanisms, where the PAM module fails to enforce proper access restrictions for accounts that should be inactive. This vulnerability directly impacts the principle of least privilege and account lifecycle management, creating potential security risks for systems relying on NIS for user authentication and authorization.
The technical implementation of this vulnerability stems from inadequate access control mechanisms within the PAM configuration for NIS account handling. When an NIS account is disabled, the system should prevent any authentication attempts or access permissions from being granted to that account. However, the flaw allows unauthorized access to remain possible even after account disabling has been processed. This occurs due to improper state management within the PAM modules that handle NIS authentication, where the disabled account status is not properly enforced or checked during the authentication process. The vulnerability manifests as a failure to maintain consistent account access control states across authentication modules, creating a persistent access vector for compromised or disabled accounts.
The operational impact of this vulnerability extends beyond simple authentication bypasses and represents a significant risk to system security and integrity. An attacker who gains knowledge of a disabled NIS account could potentially exploit this flaw to maintain unauthorized access to system resources, effectively circumventing account management procedures. This weakness undermines the fundamental security posture of systems relying on NIS for user management, as it allows for continued access to potentially compromised accounts. The vulnerability particularly affects environments where NIS is used for centralized authentication and account management, creating potential for privilege escalation and persistent access within networked systems. Organizations may experience unauthorized access to sensitive data, system resources, and potentially facilitate further attacks through compromised account credentials.
The security implications of this vulnerability align with CWE-284, which addresses improper access control in authentication mechanisms, and can be mapped to ATT&CK technique T1078 for valid accounts and T1566 for social engineering attacks that exploit weak authentication controls. Mitigation strategies should focus on immediate system updates and patches to address the PAM module implementation, followed by comprehensive account review processes to identify and secure any potentially compromised accounts. Organizations should implement additional monitoring for authentication attempts on disabled accounts, enforce stricter access controls through firewall rules, and consider implementing account lockout mechanisms beyond the standard NIS account disabling procedures. Regular security audits of authentication systems and PAM module configurations should be conducted to identify similar implementation flaws that may exist in other authentication frameworks or operating system versions.