CVE-2000-0143 is a vulnerability in the OpenSSH server (sshd) versions 1.2 through 1.2.27, discovered and published in February 2000. The flaw allows local users who do not have shell access on the system to redirect TCP connections through sshd to services that authenticate using the standard system password database, such as POP or FTP servers. Essentially, this means that a restricted local user account, which normally would not have interactive shell access, can leverage the SSH daemon to proxy or tunnel TCP connections to other services on the host or network. This redirection capability can be abused to bypass access controls or monitoring that would otherwise prevent such connections. The vulnerability arises because sshd improperly allows port forwarding or TCP redirection for users without shell access, which is a misconfiguration or design oversight in early OpenSSH versions. The CVSS v2 score is 4.6 (medium severity), reflecting that the attack vector is local (AV:L), requires low attack complexity (AC:L), no authentication (Au:N) is needed beyond local user access, and the impact affects confidentiality, integrity, and availability (C:P/I:P/A:P). No patches or fixes are available for these legacy versions, and no known exploits have been reported in the wild. However, the vulnerability is significant in environments where restricted local accounts exist and where services relying on system password authentication are present and sensitive.

For European organizations, the impact of this vulnerability depends on the presence of legacy OpenSSH versions (1.2.x) in their infrastructure, which is unlikely in modern environments but possible in legacy or embedded systems. If exploited, local users without shell access could tunnel connections to sensitive services like POP or FTP, potentially bypassing network segmentation or access controls. This could lead to unauthorized data access, credential interception, or lateral movement within internal networks. Confidentiality is at risk as attackers could intercept or redirect sensitive communications. Integrity and availability could also be compromised if attackers manipulate or disrupt services via the redirected connections. Although the vulnerability requires local access, it could be leveraged by attackers who have obtained limited user accounts, elevating their capabilities. For European organizations with strict data protection regulations (e.g., GDPR), unauthorized data exposure due to this vulnerability could result in compliance violations and reputational damage. The risk is higher in organizations with legacy Unix/Linux systems still running outdated OpenSSH versions and using system password-based authentication for services.

Given that no official patches are available for the affected OpenSSH versions, European organizations should prioritize upgrading to supported, modern OpenSSH releases that have addressed this vulnerability and improved access control mechanisms. Where upgrading is not immediately feasible, organizations should audit and restrict local user accounts to prevent unauthorized access, especially accounts without shell access that could exploit this vulnerability. Disabling TCP forwarding or port redirection features in sshd configuration for untrusted users can mitigate exploitation risks. Additionally, services relying on system password authentication (e.g., POP, FTP) should be replaced or secured with stronger authentication methods such as PAM modules, two-factor authentication, or by migrating to more secure protocols (e.g., IMAP over SSL, SFTP). Network segmentation and firewall rules should be enforced to limit internal traffic flows and prevent unauthorized redirection. Continuous monitoring and logging of SSH sessions and port forwarding activities can help detect suspicious behavior. Finally, organizations should conduct regular security assessments to identify legacy software and remove or isolate vulnerable systems.