CVE-2005-2949 in Pam Per User
Summary
by MITRE
pam_per_user before 0.4 does not verify if the user name changes between authentication attempts and uses the same subrequest handle, which allows remote attackers or local users to login as other users by using certain applications that allow the username to be changed during authentication, such as /bin/login.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 06/24/2018
The vulnerability described in CVE-2005-2949 represents a critical authentication bypass flaw in the pam_per_user pluggable authentication module version 0.3 and earlier. This issue stems from a fundamental design weakness in how the module handles user session management during the authentication process. The vulnerability specifically affects systems that utilize the Pluggable Authentication Modules framework, which is a standard component in unix-like operating systems for handling user authentication. The flaw exists because pam_per_user fails to properly validate user identity consistency between multiple authentication attempts within the same session, creating an exploitable condition that can be leveraged by malicious actors.
The technical root cause of this vulnerability lies in the improper handling of authentication state management within the pam_per_user module. When a user attempts to authenticate through applications that support dynamic username changes during the authentication process, the module fails to verify whether the username has been modified between successive authentication requests. This occurs because the module reuses the same subrequest handle for multiple authentication attempts without validating that the user identity remains consistent. The vulnerability is particularly concerning because it operates at the authentication module level, meaning it can be exploited by both remote attackers and local users who have access to applications that support username modification during authentication. The specific application mentioned is /bin/login, which is a fundamental component of unix-like systems and represents a common entry point for exploitation.
The operational impact of this vulnerability is severe and far-reaching across multiple security domains. An attacker who successfully exploits this vulnerability can achieve unauthorized access to accounts belonging to other users, effectively bypassing the authentication mechanism entirely. This type of privilege escalation can lead to complete system compromise, data theft, and persistent access to network resources. The vulnerability affects the core authentication integrity of systems using pam_per_user, which is widely deployed across various unix and linux distributions. From an attack perspective, this flaw aligns with the attack technique described in the attack pattern taxonomy where an attacker manipulates the authentication flow to gain unauthorized access. The vulnerability also maps to CWE-285, which deals with improper authorization in authentication modules, and represents a clear violation of the principle of least privilege in system security design.
Mitigation strategies for this vulnerability should focus on immediate remediation through software updates to version 0.4 or later, which contains the necessary fixes for proper user identity validation. System administrators should also implement additional security controls such as monitoring for unusual authentication patterns and implementing proper session management policies. The fix typically involves ensuring that the authentication module properly validates user identity consistency between authentication attempts and does not reuse authentication handles when user credentials have changed. Organizations should also consider implementing additional authentication layers such as multi-factor authentication to provide defense in depth against similar vulnerabilities. Regular security audits of authentication modules and proper patch management procedures should be enforced to prevent similar issues from arising in the future. The vulnerability serves as a reminder of the critical importance of proper state management in security-critical components and the necessity of thorough testing of authentication flows under various operational conditions.