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Insecure functionality

Need​

Secure functionality implementation

Context​

  • Usage of Java for building cross-platform applications
  • Usage of javax.servlet.http.HttpServletRequest for handling HTTP requests in Java Servlets
  • Usage of HttpServletResponse for handling HTTP response in Java Servlets
  • Usage of java.io.IOException for handling input/output exceptions in Java
  • Usage of java.lang.Runtime for interacting with the Java runtime environment

Description​

Non compliant code​

import javax.servlet.http.*;

public class InsecureServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) {
        String cmd = request.getParameter("cmd");
        try {
            Runtime.getRuntime().exec(cmd);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

This code represents a Servlet which accepts HTTP GET requests. The Servlet is part of a backend application that uses javax.servlet.

The vulnerability lies in the doGet method. This method retrieves a parameter named "cmd" from the incoming HTTP request. Without any validation or sanitization, it directly uses this parameter to execute a system command via Runtime.getRuntime().exec(cmd).

This is an insecure functionality because an attacker can send a GET request with any system command they want in the "cmd" parameter. The system will then execute this command, giving the attacker the ability to negatively impact the system. This could range from benign commands (like listing directory contents) to harmful ones (like deleting files or stopping services).

For example, an attacker could send a request like http://example.com/insecure?cmd=rm -rf / which would result in the deletion of all files in the system.

This is a critical security flaw known as Command Injection. It allows an attacker to execute arbitrary commands on the host operating system.

Steps​

  • Input validation: Validate and sanitize all user inputs to prevent any malicious commands from being executed.
  • Principle of Least Privilege: Ensure that the code is running with the minimum necessary privileges to limit the potential impact of any malicious commands.
  • Use a secure alternative: Instead of executing arbitrary commands, consider using safer alternatives such as predefined functions or APIs.
  • Implement proper error handling: Handle exceptions and errors gracefully to prevent sensitive information from being exposed to attackers.
  • Regularly update and patch dependencies: Keep all dependencies up to date to mitigate any known vulnerabilities that could be exploited.
  • Perform security testing: Conduct regular security testing, such as penetration testing and code reviews, to identify and fix any potential vulnerabilities.

Compliant code​

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

public class SecureServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request, HttpServletResponse response) {
        String cmd = request.getParameter("cmd");

        // Validate the command
        if (!isValidCommand(cmd)) {
            throw new IllegalArgumentException("Invalid command");
        }

        try {
            // Execute the command using a secure API
            executeSecureCommand(cmd);
        } catch (IOException e) {
            // Handle the exception gracefully
            handleException(e);
        }
    }

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

    private void executeSecureCommand(String cmd) throws IOException {
        // Implement your secure command execution logic here
        // For example, use a secure API instead of Runtime.getRuntime().exec()
    }

    private void handleException(IOException e) {
        // Implement your exception handling logic here
        // For example, log the exception and show a generic error message to the user
    }
}

The original code was vulnerable because it directly executed a command that was provided by the user, which could allow an attacker to execute arbitrary commands on the system.

The fixed code mitigates this vulnerability by implementing several security best practices:

  1. Input validation: The isValidCommand() function is used to validate the user-provided command. This function should be implemented to check if the command is in a list of allowed commands, for example.

  2. Use of a secure alternative: The executeSecureCommand() function is used to execute the command in a secure manner. This function should be implemented to use a secure API instead of Runtime.getRuntime().exec(), for example.

  3. Proper error handling: The handleException() function is used to handle any exceptions that occur during the execution of the command. This function should be implemented to log the exception and show a generic error message to the user, for example.

By implementing these security best practices, the fixed code significantly reduces the risk of an attacker being able to execute arbitrary commands on the system.

References​

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