CVE-2001-1507 in OpenSSH
Summary
by MITRE
OpenSSH before 3.0.1 with Kerberos V enabled does not properly authenticate users, which could allow remote attackers to login unchallenged.
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Analysis
by VulDB Data Team • 09/24/2025
The vulnerability described in CVE-2001-1507 represents a critical authentication flaw in OpenSSH versions prior to 3.0.1 when Kerberos V authentication is enabled. This issue stems from the improper handling of authentication credentials within the Kerberos integration layer, creating a security bypass that allows unauthorized access to systems. The flaw specifically affects the authentication process where users can potentially bypass the Kerberos challenge-response mechanism entirely, enabling malicious actors to establish connections without proper credential verification.
The technical root cause of this vulnerability lies in the Kerberos authentication module implementation within OpenSSH's authentication framework. When Kerberos V is enabled, the system should enforce strict credential validation through the Kerberos protocol's challenge-response cycle. However, the flaw allows the authentication subsystem to accept connections even when the Kerberos authentication process fails or is bypassed. This occurs because the code does not properly validate the Kerberos ticket or authentication state before granting access to the system. The vulnerability specifically affects the interaction between the SSH daemon and the Kerberos authentication service, where the authentication result is not correctly checked or enforced.
From an operational perspective, this vulnerability creates a significant risk for organizations relying on Kerberos-integrated SSH access. Attackers can exploit this weakness to gain unauthorized system access without providing valid Kerberos credentials, effectively neutralizing the security benefits of Kerberos authentication. The impact extends beyond simple unauthorized access, as compromised systems can serve as entry points for further lateral movement within networks. This vulnerability particularly affects environments where SSH is used for administrative access and Kerberos is implemented for centralized authentication management, making it a prime target for attackers seeking persistent access to privileged accounts.
The flaw aligns with CWE-287 which addresses improper authentication issues in software systems, specifically targeting weak authentication mechanisms that fail to properly validate user credentials. From an attacker's perspective, this vulnerability maps to ATT&CK technique T1078 which covers valid accounts and legitimate credentials for unauthorized access. Organizations should implement immediate mitigations including upgrading to OpenSSH 3.0.1 or later versions, disabling Kerberos authentication if not required, and implementing additional monitoring for suspicious authentication patterns. Network segmentation and additional authentication layers such as multi-factor authentication should also be considered to reduce the attack surface. The vulnerability demonstrates the importance of proper authentication flow validation and the critical need for thorough security testing of integrated authentication modules in network services.