CVE-2001-0471 in SSH
Summary
by MITRE
SSH daemon version 1 (aka SSHD-1 or SSH-1) 1.2.30 and earlier does not log repeated login attempts, which could allow remote attackers to compromise accounts without detection via a brute force attack.
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Analysis
by VulDB Data Team • 10/06/2025
The vulnerability described in CVE-2001-0471 affects the SSH daemon version 1 implementation, specifically versions 1.2.30 and earlier, which represents a critical security flaw in early secure shell protocols. This issue stems from the absence of proper logging mechanisms for repeated login attempts within the SSHD-1 server implementation, creating a significant gap in security monitoring capabilities. The flaw directly impacts the ability of system administrators to detect and respond to unauthorized access attempts, fundamentally undermining the security posture of systems relying on this legacy SSH implementation.
The technical root cause of this vulnerability lies in the design of the SSH daemon's authentication logging subsystem, which fails to maintain records of failed login attempts that occur during brute force attacks. This absence of audit logging creates a blind spot in security monitoring that allows attackers to systematically attempt multiple login credentials without triggering any alerts or notifications. The vulnerability specifically affects the SSH-1 protocol implementation where the server component does not maintain a persistent record of authentication failures, making it impossible to detect patterns of suspicious activity that would typically indicate an automated attack.
The operational impact of this vulnerability is severe and multifaceted, as it enables attackers to conduct prolonged brute force attacks against SSH services without detection. This weakness allows unauthorized access to systems through credential guessing, password spraying, or dictionary attacks, with no mechanism for system administrators to identify or respond to these attempts. The lack of logging means that even if an attacker successfully compromises an account through repeated attempts, there would be no forensic evidence or immediate alert to notify administrators of the security breach, creating a window of opportunity for attackers to establish persistent access or conduct further malicious activities.
From a cybersecurity perspective, this vulnerability aligns with CWE-307, which addresses improper restriction of repeated access attempts, and represents a classic example of inadequate audit logging that violates fundamental security principles. The flaw also relates to ATT&CK technique T1110, which covers brute force attacks, as it removes the detection capability that would normally be available through log monitoring and intrusion detection systems. Organizations relying on this vulnerable SSH implementation face significant risk of undetected account compromise, potentially leading to complete system takeover and data breaches. The vulnerability demonstrates the critical importance of proper audit logging and monitoring capabilities in security systems, as it essentially removes the ability to detect and respond to automated attack vectors that are commonly employed by threat actors in modern cyber campaigns.
The recommended mitigations for this vulnerability include immediate migration to SSH protocol version 2 implementations, which provide robust logging capabilities and improved security features. System administrators should implement additional monitoring solutions such as intrusion detection systems, fail2ban configurations, or custom logging scripts to compensate for the missing audit trail. Network-level protections such as port knocking, rate limiting, and firewall rules can also help reduce the attack surface. Organizations should also establish proper security monitoring procedures that include regular log reviews and automated alerting mechanisms to detect unauthorized access attempts. The most effective long-term solution involves complete replacement of the vulnerable SSH-1 implementation with modern SSH-2 compliant software that provides comprehensive logging and audit capabilities as specified in industry standards and best practices for secure remote access implementations.