CVE-2001-0553 in SSH
Summary
by MITRE
SSH Secure Shell 3.0.0 on Unix systems does not properly perform password authentication to the sshd2 daemon, which allows local users to gain access to accounts with short password fields, such as locked accounts that use "NP" in the password field.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 10/05/2025
The vulnerability described in CVE-2001-0553 represents a critical authentication flaw in SSH Secure Shell version 3.0.0 running on unix systems. This issue specifically affects the sshd2 daemon's password authentication mechanism, creating a significant security weakness that can be exploited by local attackers. The vulnerability stems from improper handling of password validation processes within the sshd2 service, particularly when dealing with accounts that have been locked or have specific password field configurations.
The technical flaw manifests when the sshd2 daemon processes authentication requests for accounts with short password fields or accounts that have been locked using the "NP" indicator in the password field. This particular configuration typically indicates that an account is locked or has no valid password set, yet the vulnerable version of the sshd2 daemon fails to properly validate these conditions. The authentication process becomes bypassed or weakened, allowing local users to potentially gain unauthorized access to accounts that should remain protected. This represents a fundamental failure in access control validation and authentication logic within the secure shell implementation.
The operational impact of this vulnerability is substantial as it enables local privilege escalation attacks against systems running the affected sshd2 daemon. Attackers can exploit this weakness to access accounts that have been intentionally locked or restricted, potentially compromising system integrity and confidentiality. The vulnerability particularly affects accounts with "NP" in their password fields, which are typically used to indicate that an account is disabled or has no password, yet the flawed authentication mechanism fails to properly enforce these restrictions. This creates a backdoor access path that can be leveraged by malicious local users to escalate their privileges and gain unauthorized system access.
Organizations running SSH Secure Shell 3.0.0 on unix systems face significant security risks from this vulnerability, as it undermines the fundamental security assumptions of account locking and password authentication. The issue falls under the category of improper authentication validation as classified by CWE-287, which addresses weaknesses in authentication mechanisms that allow unauthorized access. This vulnerability can be mapped to ATT&CK technique T1078.001 which covers valid accounts and T1566 which covers credential harvesting, as attackers can exploit this flaw to obtain unauthorized access to locked accounts. The risk is compounded by the fact that this vulnerability affects local users, meaning that any user with access to the system can potentially exploit it without requiring external network access or additional credentials.
Mitigation strategies for this vulnerability include immediate patching of the SSH Secure Shell implementation to version 3.1.0 or later, which contains the necessary fixes for the authentication flaw. System administrators should also implement additional security controls such as monitoring for unauthorized authentication attempts and ensuring that accounts with "NP" indicators are properly restricted. Disabling unnecessary local accounts and enforcing strong password policies can help reduce the attack surface. Additionally, organizations should conduct thorough security assessments to identify any other instances of the vulnerable sshd2 daemon and ensure that proper access controls are in place to prevent local privilege escalation attacks. Regular security updates and vulnerability management processes are essential to prevent similar issues from occurring in the future, as this vulnerability demonstrates the critical importance of proper authentication validation in security-critical systems.