CVE-2001-1169 in S-Key
Summary
by MITRE
keyinit in S/Key does not require authentication to initialize a one-time password sequence, which allows an attacker who has gained privileges to a user account to create new one-time passwords for use in other activities that may use S/Key authentication, such as sudo.
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Analysis
by VulDB Data Team • 04/08/2019
The vulnerability described in CVE-2001-1169 resides within the S/Key authentication system, a widely deployed one-time password mechanism that was prevalent in Unix and Linux environments during the late 1990s and early 2000s. This flaw specifically affects the keyinit component, which serves as the initialization tool for S/Key one-time password sequences. The vulnerability represents a critical design flaw that undermines the fundamental security assumptions of the system. S/Key was designed to provide strong authentication by requiring users to enter a unique password that changes with each login attempt, thereby protecting against replay attacks and password interception. The vulnerability stems from the fact that keyinit does not enforce authentication checks before allowing the initialization of new one-time password sequences, creating a significant security gap that can be exploited by malicious actors with access to user accounts.
The technical nature of this vulnerability can be classified under CWE-284, which describes improper access control, specifically weak access control mechanisms in authentication systems. The flaw allows an attacker who has already gained access to a user account to manipulate the S/Key password sequence without requiring additional authentication. This occurs because the keyinit utility operates without verifying that the requesting user possesses legitimate authorization to modify their password sequence. When an attacker executes keyinit, they can generate new one-time passwords that will be accepted by systems using S/Key authentication, effectively enabling them to bypass the security controls that S/Key was designed to enforce. The vulnerability is particularly dangerous because it allows privilege escalation and credential reuse attacks, where the attacker can generate new valid passwords that will authenticate against systems protected by S/Key, including critical administrative functions like sudo access.
The operational impact of this vulnerability extends far beyond simple password manipulation, as it fundamentally compromises the integrity of the authentication infrastructure. An attacker with access to a user account can create new valid one-time passwords that can be used to authenticate to systems protected by S/Key, including those that provide administrative privileges through sudo or similar mechanisms. This creates a scenario where an attacker can escalate privileges and gain unauthorized access to sensitive systems and data. The vulnerability enables persistent access patterns since the attacker can continue generating new valid passwords as needed, making detection more difficult and prolonging the compromise. From an attacker's perspective, this represents a low-effort, high-impact attack vector that can be exploited in conjunction with other techniques to maintain access to target systems. The vulnerability also impacts the trust model of S/Key, as it demonstrates that the system cannot rely on the assumption that only legitimate users can modify their password sequences.
Mitigation strategies for this vulnerability must address both the immediate security flaw and the broader authentication architecture. The most direct solution involves patching the keyinit utility to enforce proper authentication checks before allowing password sequence initialization. This requires implementing access control mechanisms that verify the identity of users attempting to modify their S/Key sequences, typically through the use of existing authentication mechanisms like password verification or privilege checks. Organizations should also implement additional monitoring and logging around keyinit usage to detect unauthorized access attempts and sequence modifications. The vulnerability highlights the importance of principle of least privilege in authentication systems, where even legitimate users should not be able to bypass normal authentication procedures for critical system functions. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques and credential access patterns, particularly those involving authentication token manipulation and the exploitation of weak access controls. Security administrators should also consider implementing additional layers of authentication for critical systems, such as multi-factor authentication, to reduce the impact of such vulnerabilities. The incident underscores the necessity of comprehensive security testing and code review for authentication components, as well as the importance of validating that all system components enforce proper access controls and authentication requirements.