CVE-2001-1473 in SSH
Summary
by MITRE
The SSH-1 protocol allows remote servers to conduct man-in-the-middle attacks and replay a client challenge response to a target server by creating a Session ID that matches the Session ID of the target, but which uses a public key pair that is weaker than the target s public key, which allows the attacker to compute the corresponding private key and use the target s Session ID with the compromised key pair to masquerade as the target.
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Analysis
by VulDB Data Team • 09/25/2025
The vulnerability described in CVE-2001-1473 represents a critical weakness in the SSH-1 protocol that fundamentally undermines the security assumptions of secure remote authentication. This flaw operates at the core of SSH's session management and key exchange mechanisms, creating a pathway for sophisticated man-in-the-middle attacks that can compromise the integrity of authenticated connections. The vulnerability specifically targets the Session ID generation process and public key validation procedures that were inherent to the SSH-1 implementation, making it particularly dangerous given the widespread adoption of SSH-1 during the late 1990s and early 2000s.
The technical flaw exploits the deterministic nature of Session ID generation within SSH-1, where attackers can predict or manipulate Session IDs to match those of legitimate target systems. This vulnerability stems from inadequate cryptographic randomness and insufficient verification of key strength during the authentication process. When a client connects to a server, the SSH-1 protocol establishes a Session ID that should be unique and unpredictable, but in this case, attackers can generate Session IDs that match legitimate ones while using weaker cryptographic keys. The attack specifically targets the public key exchange mechanism where the protocol does not adequately validate the strength of the public key presented by the server, allowing attackers to substitute their own keys that are mathematically weaker but still sufficient to compromise the session.
The operational impact of this vulnerability extends far beyond simple authentication bypass, as it enables attackers to conduct sophisticated session hijacking operations that can go undetected for extended periods. An attacker who successfully executes this attack can intercept and manipulate communications between legitimate clients and servers, potentially gaining access to sensitive data, credentials, and system resources. The vulnerability particularly affects environments where SSH-1 was deployed for secure remote administration, file transfers, and network services, creating a significant risk for organizations that had not yet transitioned to the more secure SSH-2 protocol. This attack vector is especially concerning because it can be executed without requiring direct access to the target network, making it a serious threat to distributed systems and remote access infrastructure.
The attack technique described in this vulnerability aligns with several tactics and techniques documented in the MITRE ATT&CK framework, specifically relating to credential access and privilege escalation through man-in-the-middle attacks. From a CWE perspective, this vulnerability maps to CWE-310, which covers cryptographic weaknesses, and CWE-312, which addresses cleartext storage of sensitive data. The vulnerability also demonstrates characteristics of CWE-295, which deals with improper certificate validation, and CWE-306, which addresses missing authentication. Organizations should implement immediate mitigations including mandatory migration to SSH-2 protocol, implementation of strict key validation policies, and deployment of network monitoring tools to detect anomalous Session ID patterns. The most effective long-term solution involves complete phasing out of SSH-1 implementations and adoption of modern cryptographic standards that properly address the weaknesses present in the original SSH protocol specification.