CVE-1999-1422 in Linux
Summary
by MITRE
The default configuration of Slackware 3.4, and possibly other versions, includes . (dot, the current directory) in the PATH environmental variable, which could allow local users to create Trojan horse programs that are inadvertently executed by other users.
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Analysis
by VulDB Data Team • 06/23/2021
The vulnerability described in CVE-1999-1422 represents a classic and fundamental security flaw in Unix-like operating system configurations that has persisted in various forms throughout computing history. This issue specifically affects the default PATH environment variable configuration in Slackware 3.4 and potentially other versions, where the current directory denoted by a single dot character is included in the system's PATH variable. The PATH environment variable serves as a critical component in Unix-like systems, defining the locations where the operating system searches for executable programs when a user types a command. When the current directory is included in this variable, it creates a dangerous situation where any executable file in the current working directory can be executed simply by typing its name without specifying the full path.
The technical flaw exploits the fundamental behavior of how Unix-like systems resolve command execution paths. When a user types a command such as ls or who, the system searches through each directory listed in the PATH variable in order, beginning with the first directory listed. If the current directory '.' appears early in the PATH, and a malicious user creates an executable file named ls in their current directory, any user who navigates to that directory and types ls will inadvertently execute the malicious version rather than the legitimate system command. This vulnerability is particularly insidious because it relies on the trust users place in simple command execution, making it difficult to detect and prevent. The flaw essentially creates a race condition where the system's security model is bypassed through a simple configuration error, allowing for privilege escalation and unauthorized code execution.
The operational impact of this vulnerability extends beyond simple command substitution to encompass broader security implications for system integrity and user trust. Local users with access to any directory can effectively compromise the security of other users who may execute commands in that directory without being aware of the potential threat. This creates a scenario where an attacker could place malicious executables in shared directories, network mounts, or even in directories that users routinely navigate to, leading to widespread compromise. The vulnerability affects the principle of least privilege by allowing unauthorized code execution, and it undermines the security model of Unix-like systems where the PATH variable is designed to provide controlled access to system commands. From an attack perspective, this vulnerability aligns with the ATT&CK technique of privilege escalation through environment variable manipulation and represents a form of Trojan horse attack that has been documented in various security contexts.
The implications of this vulnerability are particularly severe in multi-user environments where users share directories or where system administrators may not be aware of the PATH configuration. Security professionals should recognize this issue as a classic example of how configuration errors can create security vulnerabilities, similar to issues classified under CWE-427 Uncontrolled Search Path Element. The vulnerability demonstrates the importance of proper system hardening and configuration management, particularly in environments where multiple users interact with shared filesystems. Organizations should implement regular security audits to verify PATH variable configurations, ensuring that the current directory is not included in critical system paths. The recommended mitigations include modifying the PATH variable to remove the current directory, implementing proper file permissions, and educating users about the risks of executing unknown commands in directories they do not fully trust. This vulnerability also highlights the need for security-conscious default configurations in operating system distributions, as the default installation should not create security vulnerabilities that require manual intervention to resolve.