CVE-2001-1585 in OpenSSH
Summary
by MITRE
SSH protocol 2 (aka SSH-2) public key authentication in the development snapshot of OpenSSH 2.3.1, available from 2001-01-18 through 2001-02-08, does not perform a challenge-response step to ensure that the client has the proper private key, which allows remote attackers to bypass authentication as other users by supplying a public key from that user s authorized_keys file.
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Analysis
by VulDB Data Team • 09/24/2025
The vulnerability described in CVE-2001-1585 represents a critical flaw in the SSH protocol 2 implementation within OpenSSH version 2.3.1 development snapshot. This issue emerged during a specific timeframe from January 18 to February 8, 2001, when the development team was working on what would become the 2.3.1 release. The flaw fundamentally undermines the security assurances provided by public key authentication mechanisms, which are designed to establish trust between client and server through cryptographic verification processes. The vulnerability specifically targets the challenge-response protocol that should validate possession of the corresponding private key, creating an authentication bypass opportunity for malicious actors.
The technical root cause of this vulnerability lies in the absence of proper challenge-response validation within the SSH-2 public key authentication flow. In a properly implemented system, when a client presents a public key for authentication, the server should generate a cryptographic challenge that requires the client to demonstrate possession of the corresponding private key through a mathematical operation. This process ensures that only entities with access to the private key can successfully authenticate. However, in the affected OpenSSH 2.3.1 development snapshot, this crucial step was omitted, allowing attackers to present any public key from a target user's authorized_keys file and successfully authenticate as that user. This flaw directly maps to CWE-287, which addresses improper authentication issues in systems where authentication mechanisms are not properly enforced.
The operational impact of this vulnerability is severe and far-reaching for systems utilizing the affected OpenSSH version. Attackers can exploit this weakness to gain unauthorized access to systems as any user whose public key exists in the authorized_keys file, effectively bypassing the entire purpose of public key authentication. This creates a significant privilege escalation vector where an attacker with minimal access can potentially move laterally throughout a network by simply collecting public keys from various user accounts. The vulnerability also has implications for compliance with security standards such as those outlined in the NIST Special Publication 800-53, which emphasizes the importance of proper authentication controls and access management. From an attacker's perspective, this flaw aligns with techniques described in the MITRE ATT&CK framework under the authentication bypass category, specifically targeting the T1078 credential access tactic.
The exploitation of this vulnerability demonstrates a fundamental breakdown in the cryptographic security model of SSH-2 implementations. The absence of challenge-response validation creates a scenario where the system accepts authentication requests based solely on the presentation of a valid public key, without verifying that the corresponding private key is actually possessed by the requesting entity. This weakness essentially transforms what should be a robust cryptographic authentication system into a mechanism that can be easily circumvented through simple key substitution. Organizations relying on the affected OpenSSH versions would have experienced a complete compromise of their SSH-based authentication security posture, as the vulnerability allowed for impersonation attacks that could be executed remotely without requiring knowledge of user passwords or additional credentials. The remediation for this issue required the implementation of proper challenge-response mechanisms in the SSH-2 protocol implementation, ensuring that all authentication attempts required cryptographic proof of private key possession before granting access rights.