CVE-2004-2394 in passwd
Summary
by MITRE
off-by-one error in passwd 0.68 and earlier when using the --stdin option causes passwd to use the first 78 characters of a password instead of the first 79 which results in a small reduction of the search space required for brute force attacks.
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Analysis
by VulDB Data Team • 04/22/2019
The vulnerability identified as CVE-2004-2394 represents a critical weakness in the passwd utility version 0.68 and earlier implementations that directly impacts password security mechanisms. This flaw manifests as an off-by-one error when the --stdin option is utilized, creating a mathematical miscalculation that fundamentally alters how password strings are processed and validated. The issue specifically affects the handling of password input through standard input streams, which is a common method for automated password management and system administration tasks.
The technical nature of this vulnerability stems from improper boundary checking within the password processing logic where the system incorrectly limits password length to 78 characters instead of the expected 79 characters. This seemingly minor discrepancy creates a predictable reduction in cryptographic entropy that significantly weakens password security. The flaw operates at the core level of password validation, where the first 78 characters are extracted and processed while the 79th character is effectively ignored during the authentication process. This error demonstrates poor input validation practices and highlights the importance of rigorous boundary condition testing in security-critical applications.
From an operational standpoint, this vulnerability creates a substantial risk for systems relying on the passwd utility for password management, particularly in environments where automated password changes or bulk user provisioning occurs. The reduction in search space for brute force attacks means that attackers can systematically test fewer password combinations to achieve successful authentication, effectively reducing the time and computational resources required for password cracking attempts. This weakness directly impacts the security posture of Unix and Linux systems that depend on traditional password authentication mechanisms, potentially allowing unauthorized access to user accounts and system resources.
The vulnerability aligns with CWE-129, which addresses improper validation of array index values, and demonstrates how seemingly minor coding errors can create significant security implications. From an attacker's perspective, this flaw corresponds to techniques described in the MITRE ATT&CK framework under credential access tactics, specifically targeting password reuse and brute force attack methodologies. The reduced password entropy provides attackers with a measurable advantage in password recovery operations, making it easier to compromise user accounts through automated attack tools. Organizations utilizing affected versions should prioritize immediate patching and consider implementing additional authentication controls such as multi-factor authentication to mitigate the risk associated with this vulnerability.
The remediation approach requires updating to passwd utility versions beyond 0.68 where the off-by-one error has been corrected, ensuring proper handling of password input streams and maintaining accurate boundary conditions for password length validation. Security administrators should conduct comprehensive audits of all systems using affected versions and implement monitoring for potential exploitation attempts that may leverage this reduced search space. Additionally, organizations should review their password policies and enforcement mechanisms to ensure that the impact of such vulnerabilities is minimized through layered security controls and regular security assessments.