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NoSQL injection

Need​

Prevention of NoSQL injection attacks

Context​

  • Usage of Java 8 for developing applications with enhanced features and performance
  • Usage of javax.servlet-api for Java Servlet development
  • Usage of mongodb-driver for interacting with MongoDB database

Description​

Non compliant code​

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.mongodb.*;

public class VulnerableServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) {
        MongoClient mongoClient = new MongoClient();
        DB db = mongoClient.getDB("mydb");
        DBCollection collection = db.getCollection("users");

        String user = request.getParameter("user");
        String password = request.getParameter("password");

        BasicDBObject query = new BasicDBObject();
        query.put("user", user);
        query.put("password", password);

        DBObject dbObject = collection.findOne(query);
    }
}

This Java servlet is vulnerable to NoSQL injection. It uses the MongoDB Java driver to connect to a MongoDB database and perform a query on the users collection.

The servlet retrieves the user and password parameters from the HTTP request without any validation or sanitization. These parameters are directly used to construct a MongoDB query, which is then executed to find a user document in the database that matches the provided user and password.

An attacker could exploit this vulnerability by sending a specially crafted request that modifies the structure of the query. For example, they could provide a user parameter that is a MongoDB operator instead of a simple string, which could allow them to bypass authentication or even retrieve sensitive information from the database.

This vulnerability could be mitigated by validating and sanitizing the user input before using it in the query. For example, the application could check that the user and password parameters are strings of a reasonable length, and do not contain any special characters or operators that could be used in a MongoDB query.

Steps​

  • Validate and sanitize user inputs: Before using any user input in a NoSQL query, ensure that it is properly validated and sanitized to prevent any malicious input.
  • Use parameterized queries: Instead of dynamically generating queries with user inputs, use parameterized queries or prepared statements provided by the database driver. This ensures that user inputs are treated as data and not as part of the query structure.
  • Implement input validation and whitelisting: Validate user inputs against a predefined set of allowed characters or patterns. Use whitelisting to only allow specific characters or patterns in the input.
  • Limit privileges: Ensure that the database user used by the application has the minimum required privileges to perform the necessary operations. Avoid using a superuser account for database connections.
  • Implement access controls: Implement proper access controls to restrict the types of queries that can be executed by the application. Only allow necessary operations on specific collections or documents.
  • Implement rate limiting and request throttling: Implement mechanisms to limit the number of requests that can be made within a certain time period. This helps prevent brute-force attacks and reduces the impact of any successful injection attempts.
  • Regularly update and patch dependencies: Keep all dependencies, including the database driver, up to date with the latest security patches and updates.
  • Perform security testing and code reviews: Regularly perform security testing, including penetration testing and code reviews, to identify and fix any vulnerabilities in the application code.

Compliant code​

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.mongodb.*;
import org.bson.Document;
import java.util.regex.Pattern;

public class SecureServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response) {
        MongoClient mongoClient = new MongoClient();
        MongoDatabase db = mongoClient.getDatabase("mydb");
        MongoCollection<Document> collection = db.getCollection("users");

        String user = request.getParameter("user");
        String password = request.getParameter("password");

        // Validate and sanitize user inputs
        if (isValid(user) && isValid(password)) {
            Document query = new Document();
            query.append("user", user);
            query.append("password", password);

            Document dbObject = collection.find(query).first();
        }
    }

    // Input validation function
    private boolean isValid(String input) {
        // Define allowed pattern
        Pattern pattern = Pattern.compile("[a-zA-Z0-9]*");
        // Check if input matches the allowed pattern
        return pattern.matcher(input).matches();
    }
}

The updated code includes a validation function isValid() that checks if the user input matches a predefined pattern. This pattern only allows alphanumeric characters, effectively preventing any special characters that could be used in an injection attack.

The doGet() method now calls this validation function for both the username and password parameters before using them in the NoSQL query. If either input is invalid, the query is not executed.

This approach ensures that user inputs are treated as data and not as part of the query structure, effectively mitigating the risk of NoSQL injection attacks.

Please note that this is a basic example and real-world applications may require more complex validation and sanitization methods. Also, it's important to implement other security measures such as access controls, rate limiting, and regular security testing as part of a comprehensive security strategy.

References​

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