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Inappropriate coding practices - relative path command

Need​

Enforce secure coding practices to prevent the use of relative path commands

Context​

  • Usage of Java for building robust and scalable applications
  • Usage of javax.servlet for building Java web applications with Servlet technology
  • Usage of java.io for input and output operations in Java

Description​

Non compliant code​

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;

public class VulnerableServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String command = "../relative/path/command";
        Runtime.getRuntime().exec(command);
    }
}

The above code represents a servlet in Java that uses a relative path to execute a command. The doGet method, which responds to HTTP GET requests, contains a string command that specifies a relative path to an executable command.

The Runtime.getRuntime().exec(command) line is where the vulnerability lies. This line executes the command specified in the command string. Since the path is relative, it depends on the current working directory, which could be manipulated by an attacker.

For instance, if an attacker can control the current working directory, they can make the command string point to a malicious executable, thus compromising the system. This is a major security risk, as it can lead to arbitrary code execution, privilege escalation, or even a complete system takeover.

Furthermore, the use of Runtime.getRuntime().exec(command) can lead to command injection vulnerabilities if the command string includes untrusted input. This could allow an attacker to execute arbitrary commands on the system with the privileges of the running Java process.

Steps​

  • Avoid using relative paths when executing commands.
  • Use absolute paths instead to ensure that the correct executable is called.
  • Validate and sanitize user input to prevent any malicious commands from being executed.
  • Implement proper access controls and permissions to restrict the execution of commands to authorized users only.
  • Regularly update and patch the system to ensure that any known vulnerabilities are addressed.

Compliant code​

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;

public class SecureServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String command = "/absolute/path/command";
        if(validateCommand(command)){
            Runtime.getRuntime().exec(command);
        }
    }

    private boolean validateCommand(String command){
        // Implement your command validation logic here
        // For example, check if the command is in the list of allowed commands
        return true;
    }
}

The updated code now uses an absolute path when executing the command, which ensures that the correct executable is called. This mitigates the risk of an attacker manipulating environment variables or PATH to compromise the system.

The validateCommand function is a placeholder for the logic that validates the command before execution. This could involve checking if the command is in a list of allowed commands, or sanitizing the command to remove any potentially harmful input.

It's important to note that this code still requires proper access controls and permissions to be implemented to restrict the execution of commands to authorized users only. Additionally, the system should be regularly updated and patched to address any known vulnerabilities.

This code is a step towards more secure coding practices, but it's not a complete solution. It's always recommended to follow the principle of least privilege, where a process or user is given the minimum levels of access necessary to perform its tasks. This can help to further reduce the potential impact of a security vulnerability.

References​

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