CVE-2000-0143 in SSH
Summary
by MITRE
The SSH protocol server sshd allows local users without shell access to redirect a TCP connection through a service that uses the standard system password database for authentication, such as POP or FTP.
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Analysis
by VulDB Data Team • 10/19/2025
The vulnerability described in CVE-2000-0143 represents a significant security flaw in the Secure Shell protocol implementation, specifically within the sshd server component. This issue affects systems where SSH is used for remote access and authentication, creating a pathway for local users who lack direct shell privileges to exploit network service redirection capabilities. The vulnerability stems from improper handling of TCP connection forwarding mechanisms within the SSH protocol implementation, allowing unauthorized redirection of network traffic through services that rely on standard system password databases for authentication.
The technical flaw manifests when local users with restricted access attempt to utilize SSH's port forwarding capabilities to redirect TCP connections through services such as POP3 or FTP servers. These services typically authenticate users against the standard system password database, which is accessible through the established SSH connection. The vulnerability occurs because the sshd server fails to properly validate or restrict the forwarding of connections to services that may be exploited for unauthorized access. This misconfiguration allows attackers to potentially bypass normal authentication mechanisms and gain access to services that would otherwise be protected by their respective authentication schemes.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it creates a vector for lateral movement within network environments. Attackers can leverage this flaw to redirect traffic through services that may have weaker security controls or different authentication mechanisms than the primary SSH access point. The vulnerability particularly affects environments where multiple services share the same authentication database, creating a chain reaction where compromise of one service can lead to access of others. This type of vulnerability aligns with CWE-284, which addresses improper access control in software implementations, and represents a classic case of insufficient privilege separation in network service handling.
Organizations implementing SSH services must consider the broader implications of this vulnerability, as it can be exploited to bypass traditional network security controls. The ability to redirect TCP connections through standard authentication services creates a significant risk for environments where service accounts or shared authentication mechanisms exist. Mitigation strategies should focus on implementing proper SSH configuration controls, including restricting port forwarding capabilities, enforcing strict access controls on forwarded connections, and ensuring that services with shared authentication databases are properly secured. This vulnerability demonstrates the importance of following security best practices such as those outlined in the NIST Cybersecurity Framework and aligns with ATT&CK technique T1021.004 for remote services and T1566 for credential access through network services.
The vulnerability highlights the critical need for proper network segmentation and service isolation within enterprise environments. Organizations should implement comprehensive network access controls that prevent unauthorized redirection of traffic through sensitive services. Additionally, regular security audits should verify that SSH implementations properly enforce access controls and do not permit unauthorized forwarding of connections to services that may be exploited. System administrators must ensure that SSH server configurations follow security guidelines and that unnecessary forwarding capabilities are disabled to prevent exploitation of this class of vulnerability. The remediation process should include comprehensive testing of SSH configurations to verify that proper access controls are in place and that the vulnerability cannot be exploited to redirect traffic through unauthorized services.