CVE-2007-0003 in Linux
Summary
by MITRE
pam_unix.so in Linux-PAM 0.99.7.0 allows context-dependent attackers to log into accounts whose password hash, as stored in /etc/passwd or /etc/shadow, has only two characters.
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Analysis
by VulDB Data Team • 07/29/2019
The vulnerability described in CVE-2007-0003 represents a critical authentication flaw within the Linux Pluggable Authentication Modules framework, specifically affecting pam_unix.so in Linux-PAM version 0.99.7.0. This issue stems from improper validation of password hash lengths during the authentication process, creating a significant security weakness that can be exploited by context-dependent attackers. The flaw occurs when password hashes stored in system authentication files such as /etc/passwd or /etc/shadow contain only two characters, which is insufficient for secure password verification. This vulnerability directly impacts the integrity of the authentication system by allowing unauthorized access to accounts that should be protected by stronger password mechanisms.
The technical implementation of this vulnerability resides in the pam_unix.so module's handling of password verification routines where it fails to properly validate the length and format of password hashes before attempting authentication. When a password hash consists of only two characters, the authentication module does not adequately verify whether this hash represents a legitimate password or an incomplete hash value. This weakness stems from a lack of proper input validation and insufficient cryptographic requirements enforcement within the PAM authentication framework. The vulnerability specifically affects systems where weak password hashes are present in the authentication database, allowing attackers to bypass normal authentication procedures by exploiting this minimal hash length requirement.
The operational impact of CVE-2007-0003 extends beyond simple unauthorized access, as it represents a fundamental breakdown in system security controls that can lead to complete account compromise. Attackers can leverage this vulnerability to gain unauthorized access to user accounts without requiring knowledge of valid passwords, effectively bypassing the entire password-based authentication mechanism. The vulnerability is particularly dangerous because it can be exploited without prior knowledge of account credentials, making it a significant threat to system integrity and user confidentiality. This flaw affects the core authentication infrastructure of Linux systems, potentially allowing attackers to escalate privileges and move laterally within networks where such systems are deployed.
Organizations should implement immediate mitigations including updating to patched versions of Linux-PAM that properly validate password hash lengths and enforce minimum cryptographic requirements. System administrators must conduct comprehensive audits of authentication files to identify and correct accounts with weak password hashes, ensuring all passwords meet current security standards. The remediation process should include rehashing all user passwords with strong cryptographic algorithms and implementing proper password policies that enforce minimum length and complexity requirements. This vulnerability aligns with CWE-256, which addresses insecure password storage, and represents a significant concern under ATT&CK technique T1110, which covers password cracking and credential access. Additional defensive measures should include monitoring authentication logs for suspicious activity and implementing account lockout mechanisms to prevent brute force attacks against weak credentials.