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Lack of data validation - OTP

Need​

Implementation of proper data validation for OTP tokenCode parameter

Context​

  • Usage of Dart for building cross-platform mobile, web, and desktop applications
  • Usage of Shelf for managing and organizing data in a Node.js application

Description​

Non compliant code​

import 'package:shelf/shelf.dart' as shelf;

shelf.Response handleRequest(shelf.Request request) {
  var tokenCode = request.url.queryParameters['tokenCode'];

  if (tokenCode == null) {
    return shelf.Response(400, body: 'Missing tokenCode parameter');
  }

  // Here is the vulnerability, no validation of the tokenCode
  // Any random values can be used in multiple attempts
  var isTokenValid = validateToken(tokenCode);

  if (isTokenValid) {
    return shelf.Response.ok('Token is valid');
  } else {
    return shelf.Response(400, body: 'Invalid token');
  }
}

bool validateToken(String token) {
  // Simulate token validation
  return token == '123456';
}

The above code represents a handler for a request in a backend application using the shelf framework in Dart. The vulnerability lies in the handleRequest function, where the tokenCode parameter is fetched from the URL query parameters.

The tokenCode is then passed to the validateToken function to verify its validity. The issue here is that there's no evidence of validation of the values sent in the tokenCode parameter to complete the request, allowing random values to be used in multiple attempts.

This means an attacker could potentially brute force the OTP by sending multiple requests with different tokenCode values. Since there's no limit or validation on these attempts, the application is vulnerable to this type of attack.

Steps​

  • Implement a rate limiting mechanism to limit the number of attempts a user can make within a certain time period.
  • Add a check to ensure the tokenCode is not only present but also in the correct format and length.
  • Consider using a more secure method for generating and validating tokens, such as JWT or a library specifically designed for OTPs.
  • Implement a lockout mechanism after a certain number of failed attempts to prevent brute force attacks.
  • Log failed attempts and set up alerts for multiple failed attempts from the same IP address or for the same user.

Compliant code​

import 'package:shelf/shelf.dart' as shelf;
import 'package:rate_limiter/rate_limiter.dart';

// Create a memory store for rate limiting
final store = MemoryStore();

// Define the rate limiting rules
final rateLimiter = RateLimiter(store, points: 5, duration: Duration(minutes: 15));

shelf.Response handleRequest(shelf.Request request) {
  var tokenCode = request.url.queryParameters['tokenCode'];

  if (tokenCode == null || !isTokenFormatValid(tokenCode)) {
    return shelf.Response(400, body: 'Missing or invalid tokenCode parameter');
  }

  // Check if the user has exceeded the rate limit
  if (!rateLimiter.consume(request.remoteAddress)) {
    return shelf.Response(429, body: 'Too many requests');
  }

  var isTokenValid = validateToken(tokenCode);

  if (isTokenValid) {
    return shelf.Response.ok('Token is valid');
  } else {
    return shelf.Response(400, body: 'Invalid token');
  }
}

bool isTokenFormatValid(String token) {
  // Check if the token is in the correct format and length
  // This is a simple example, replace with your own validation logic
  return RegExp(r'^\\d{6}$').hasMatch(token);
}

bool validateToken(String token) {
  // Simulate token validation
  // Consider using a more secure method for generating and validating tokens
  return token == '123456';
}

The code above fixes the vulnerability by implementing several security measures:

  1. Rate Limiting: A rate limiting mechanism is implemented using the rate_limiter package. This limits the number of attempts a user can make within a certain time period (5 attempts every 15 minutes in this example). If a user exceeds this limit, a 429 (Too Many Requests) response is returned.

  2. Token Format Validation: Before validating the token, the code checks if the token is in the correct format and length using a regular expression. This is a simple example and should be replaced with your own validation logic.

  3. Token Validation: The validateToken function simulates token validation. Consider using a more secure method for generating and validating tokens, such as JWT or a library specifically designed for OTPs.

Note: This code does not implement a lockout mechanism or logging of failed attempts. These features would require a more complex setup, possibly involving a database or external logging service, and are beyond the scope of this example.

References​

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