CVE-2003-0786 in OpenSSH
Summary
by MITRE
The SSH1 PAM challenge response authentication in OpenSSH 3.7.1 and 3.7.1p1, when Privilege Separation is disabled, does not check the result of the authentication attempt, which can allow remote attackers to gain privileges.
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Analysis
by VulDB Data Team • 07/15/2024
The vulnerability described in CVE-2003-0786 represents a critical authentication flaw in OpenSSH versions 3.7.1 and 3.7.1p1 that specifically affects SSH1 PAM challenge response authentication mechanisms. This issue arises when Privilege Separation is disabled, creating a dangerous condition where the authentication subsystem fails to properly validate the outcome of authentication attempts. The flaw exists at the core of how OpenSSH handles authentication responses, particularly within the PAM (Pluggable Authentication Modules) framework that provides modular authentication capabilities for the SSH service.
The technical implementation of this vulnerability stems from a failure in the authentication flow control logic within OpenSSH's SSH1 protocol implementation. When Privilege Separation is disabled, the system should verify that authentication has successfully completed before granting access privileges. However, the code path that processes PAM challenge response authentication does not properly evaluate whether the authentication attempt actually succeeded. This creates a scenario where an attacker can potentially bypass authentication mechanisms and gain unauthorized access to systems. The vulnerability is classified under CWE-284 Access Control Flaw, specifically related to improper access control enforcement during authentication processes, and aligns with ATT&CK technique T1078 Valid Accounts for maintaining persistent access through compromised authentication mechanisms.
The operational impact of this vulnerability extends beyond simple privilege escalation to potentially enable full system compromise when exploited by remote attackers. An attacker exploiting this flaw could gain unauthorized access to systems running vulnerable OpenSSH versions, potentially leading to complete system control, data exfiltration, or use as a foothold for further network infiltration. The vulnerability is particularly dangerous because it affects the fundamental authentication process, meaning that even if an attacker cannot directly exploit the flaw through traditional means, they may be able to craft authentication responses that are accepted by the system without proper validation. This creates a significant risk for organizations relying on SSH1 authentication with PAM challenge response mechanisms.
Mitigation strategies for CVE-2003-0786 focus on both immediate remediation and long-term architectural improvements. The most direct solution involves upgrading to OpenSSH versions that contain the fix for this vulnerability, specifically versions 3.7.2 and later where the authentication result checking has been properly implemented. Organizations should also consider disabling SSH1 protocol support entirely, as SSH1 is inherently less secure than SSH2 and has been deprecated in favor of more robust authentication mechanisms. Additionally, enabling Privilege Separation should be mandatory in all configurations, as this vulnerability only manifests when this security feature is disabled. Network segmentation and access controls should be implemented to limit exposure, while monitoring systems should be configured to detect unusual authentication patterns that might indicate exploitation attempts. The fix addresses the root cause by ensuring proper authentication result validation, which aligns with security best practices outlined in NIST SP 800-53 and ISO/IEC 27001 frameworks for access control management.