CVE-2002-1469 in scponly
Summary
by MITRE
scponly does not properly verify the path when finding the (1) scp or (2) sftp-server programs, which could allow remote authenticated users to bypass access controls by uploading malicious programs and modifying the PATH variable in $HOME/.ssh/environment to locate those programs.
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Analysis
by VulDB Data Team • 11/30/2024
The vulnerability described in CVE-2002-1469 affects the scponly utility, a restricted shell designed to limit user access to secure copy operations while maintaining security through controlled execution environments. This flaw resides in the path verification mechanism that scponly employs when locating essential programs such as scp and sftp-server. The vulnerability stems from insufficient validation of the PATH environment variable, which allows authenticated remote users to manipulate the program execution flow by placing malicious executables in directories that precede the legitimate program locations within the user's PATH. The issue is particularly significant because it operates at the privilege escalation level, where an authenticated user can leverage the PATH manipulation to execute arbitrary code with elevated privileges. The vulnerability specifically targets the configuration file located in $HOME/.ssh/environment, which is used to set environment variables for the restricted shell session. When scponly searches for the required programs, it does not perform strict path validation, allowing attackers to insert malicious executables that will be executed instead of the legitimate system programs. This weakness enables attackers to bypass access controls that scponly is designed to enforce, potentially leading to full system compromise. The flaw aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, and CWE-78, which addresses improper neutralization of special elements used in OS command lines. From an operational perspective, this vulnerability creates a significant risk because it can be exploited by users who have already gained authentication access to the system, making it a particularly dangerous privilege escalation vector. The attack requires the user to have valid credentials and access to the home directory to modify the .ssh/environment file, but once successful, the attacker can execute arbitrary commands with the privileges of the scponly user. The impact extends beyond simple command execution as it undermines the fundamental security model of restricted shells, which rely on predictable program locations and controlled execution environments. According to ATT&CK framework, this vulnerability maps to T1068, which describes the use of privilege escalation techniques, and T1548.003, which covers abuse of Sudo and Sudoers configuration. The vulnerability demonstrates a classic case of insecure program execution where the system fails to validate the integrity of the program paths, allowing for path traversal attacks that bypass intended security controls. Organizations using scponly or similar restricted shell implementations should immediately implement mitigations that include strict path validation, proper access controls on configuration files, and regular auditing of environment variable settings. The vulnerability also highlights the importance of implementing principle of least privilege and ensuring that environment variables are properly sanitized before being used in program execution contexts. Security practitioners should consider implementing additional monitoring for changes to the .ssh/environment file and enforce strict file permissions to prevent unauthorized modifications. The broader implications suggest that similar vulnerabilities may exist in other restricted shell implementations that do not properly validate program paths, requiring comprehensive security assessments of all such utilities. This vulnerability represents a critical weakness in Unix-like system security models where environment variable manipulation can be used to circumvent access controls, emphasizing the need for robust input validation and secure program execution practices. The flaw demonstrates how seemingly minor implementation details in security-critical components can lead to significant privilege escalation opportunities, underscoring the importance of thorough security testing and code review processes for all system utilities that handle program execution.