CVE-2013-7041 in Pam Userdb
Summary
by MITRE
The pam_userdb module for Pam uses a case-insensitive method to compare hashed passwords, which makes it easier for attackers to guess the password via a brute force attack.
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Analysis
by VulDB Data Team • 05/03/2019
The pam_userdb module within the Pluggable Authentication Modules framework presents a significant security weakness that undermines password verification processes through improper case handling during hashed password comparison. This vulnerability specifically affects systems utilizing the userdb authentication backend where password hashes are stored and validated against user input. The flaw manifests when the module performs case-insensitive comparisons between stored password hashes and those provided during authentication attempts, creating an avenue for attackers to exploit the reduced entropy in password guessing operations. This issue directly impacts the integrity of authentication mechanisms by weakening the cryptographic strength that should protect user credentials.
The technical implementation flaw resides in the pam_userdb module's password verification routine where it employs a case-insensitive string comparison function instead of maintaining the proper case sensitivity required for cryptographic hash validation. When password hashes are generated and stored, they contain specific case-sensitive character sequences that are essential for maintaining their cryptographic properties. However, the module's flawed comparison logic allows attackers to systematically test variations of password attempts without being constrained by case sensitivity, effectively reducing the complexity of brute force attacks. This behavior violates fundamental cryptographic principles where hash comparisons must maintain strict case sensitivity to preserve the security guarantees inherent in the hashing algorithm.
The operational impact of this vulnerability extends beyond simple authentication bypasses to create a substantial risk for credential compromise across affected systems. Attackers can leverage this weakness to conduct more efficient brute force campaigns against user accounts, as the case-insensitive comparison reduces the effective search space for password guessing. Systems utilizing this module become particularly vulnerable in environments where weak passwords are prevalent, as the reduced attack surface allows for faster successful credential compromise. The vulnerability affects any authentication system relying on pam_userdb for user database authentication, potentially exposing sensitive user accounts and creating opportunities for lateral movement within compromised networks. This weakness particularly impacts enterprise environments where centralized authentication systems depend on user database backends for credential validation.
Security professionals should implement immediate mitigations including updating to patched versions of the pam_userdb module or implementing additional authentication controls such as account lockout mechanisms and multi-factor authentication. Organizations must also conduct comprehensive audits of all systems utilizing pam_userdb to identify potential exposure and ensure proper case-sensitive hash comparison implementations. The vulnerability aligns with CWE-254 weakness category related to security features that are not properly implemented, and maps to ATT&CK technique T1110.003 for password guessing attacks. Additionally, this issue demonstrates poor adherence to authentication security best practices and represents a failure to implement proper cryptographic validation procedures. Organizations should consider implementing additional monitoring for authentication attempts and establish more robust password policies to mitigate the increased risk associated with this vulnerability.