CVE-1999-0787 in SSH
Summary
by MITRE
The SSH authentication agent follows symlinks via a UNIX domain socket.
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Analysis
by VulDB Data Team • 11/02/2024
The vulnerability described in CVE-1999-0787 pertains to the Secure Shell authentication agent implementation where the system follows symbolic links when processing requests through UNIX domain sockets. This flaw exists within the ssh-agent component that manages private keys for SSH authentication, creating a potential security risk when handling file system operations through networked socket interfaces. The vulnerability stems from insufficient validation of symbolic link references during the authentication process, allowing malicious actors to manipulate the system's key handling behavior through carefully crafted symbolic link structures.
This technical weakness represents a classic case of improper input validation and path resolution handling within a privileged system component. The ssh-agent service operates with elevated privileges to manage cryptographic keys and authentication tokens, making it a critical target for attackers seeking to compromise SSH-based security infrastructure. When the agent processes requests through UNIX domain sockets, it should validate that all file references point to legitimate locations rather than traversing symbolic links that could redirect to unauthorized files or directories. The failure to properly resolve paths and validate link targets creates an attack surface where adversaries can potentially access or manipulate key material through symlink manipulation.
The operational impact of this vulnerability extends beyond simple privilege escalation scenarios, as it fundamentally undermines the trust model of SSH authentication systems. Attackers could exploit this weakness by creating malicious symbolic links that point to sensitive files such as other users' private keys, system configuration files, or critical system binaries. This allows for unauthorized key access, potential credential theft, and could enable further attacks within the compromised environment. The vulnerability affects systems where ssh-agent is actively running and processing authentication requests, particularly in multi-user environments where proper file system isolation should prevent such cross-contamination.
From a cybersecurity perspective, this vulnerability aligns with CWE-59, which describes improper link resolution without limit checks, and represents a path traversal issue within a privileged service. The attack vector follows the ATT&CK technique T1552.001 for credentials from password storage modules, specifically targeting SSH agent functionality. Mitigation strategies should include implementing strict path validation mechanisms that prevent symbolic link resolution in critical authentication contexts, disabling unnecessary symbolic link following in socket-based services, and ensuring proper file system permissions are enforced. System administrators should also consider implementing monitoring for unusual symbolic link creation patterns and regularly audit ssh-agent configurations to prevent exploitation of this and similar path traversal vulnerabilities.
The broader implications of this vulnerability highlight the importance of secure coding practices in privileged system components, particularly when handling file system operations through network interfaces. Modern security frameworks emphasize the principle of least privilege and input validation as fundamental defenses against such attacks. Organizations should implement comprehensive security controls including regular vulnerability assessments, proper system hardening, and adherence to security best practices for daemon and service implementations. The vulnerability also demonstrates the necessity of continuous security monitoring and the importance of maintaining up-to-date security patches for all system components, especially those handling cryptographic keys and authentication tokens.