CVE-2003-1562 in OpenSSH
Summary
by MITRE
sshd in OpenSSH 3.6.1p2 and earlier, when PermitRootLogin is disabled and using PAM keyboard-interactive authentication, does not insert a delay after a root login attempt with the correct password, which makes it easier for remote attackers to use timing differences to determine if the password step of a multi-step authentication is successful, a different vulnerability than CVE-2003-0190.
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Analysis
by VulDB Data Team • 07/13/2025
The vulnerability described in CVE-2003-1562 represents a significant timing side-channel attack vector within the OpenSSH implementation that affects versions 3.6.1p2 and earlier. This weakness specifically manifests when the sshd daemon operates with PermitRootLogin disabled and employs PAM keyboard-interactive authentication mechanisms. The core issue lies in the inconsistent timing behavior during authentication attempts, where successful root login attempts with correct passwords execute without the expected delay that should occur after failed attempts. This timing discrepancy creates a measurable difference that remote attackers can exploit to infer authentication success or failure through careful observation of response times.
The technical flaw stems from the improper implementation of authentication flow control within the sshd service when handling root login attempts. When a user attempts to log in as root with a valid password, the system should maintain consistent timing behavior regardless of whether the authentication succeeds or fails. However, the vulnerability allows attackers to distinguish between successful and failed authentication attempts based on timing variations, effectively creating a covert channel for password guessing attacks. This behavior directly violates the principle of constant-time execution that cryptographic and authentication systems should maintain to prevent timing-based information leakage.
From an operational perspective, this vulnerability significantly weakens the security posture of systems running vulnerable OpenSSH versions by enabling remote attackers to perform more efficient password guessing or brute force attacks. The timing differences make it easier to determine when a password is correct, potentially reducing the time required to crack root passwords through automated attacks. This vulnerability is particularly concerning because it operates at the authentication layer and can be exploited without requiring elevated privileges or complex attack vectors, making it accessible to a broad range of threat actors. The impact extends beyond simple password guessing to potentially enable privilege escalation attacks against systems where root access is the ultimate target.
The vulnerability maps to CWE-347, which specifically addresses improper certificate validation and authentication mechanisms that allow for timing-based side-channel attacks. It also aligns with ATT&CK technique T1110.004, which covers credential access through password spraying and brute force methods. Organizations using vulnerable OpenSSH implementations face increased risk of unauthorized access, particularly in environments where root credentials are valuable targets. The vulnerability demonstrates the critical importance of maintaining consistent timing behavior in authentication systems to prevent information leakage that could be exploited by attackers.
Mitigation strategies for this vulnerability require immediate patching of OpenSSH installations to versions that address the timing inconsistency in authentication handling. System administrators should also implement additional security controls such as rate limiting, account lockout mechanisms, and monitoring for unusual authentication patterns. Network-level protections including firewall rules and intrusion detection systems can help detect and block suspicious authentication attempts that might exploit this timing vulnerability. Regular security assessments should verify that authentication systems maintain consistent timing behavior across all authentication steps to prevent similar side-channel attacks from compromising system security.