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Automatic information enumeration - Personal Information


Prevention of unauthorized access to personal information


  • Usage of Dart for building cross-platform mobile, web, and desktop applications
  • Usage of Shelf for managing database queries and data modeling
  • Usage of shelf_io for managing input/output operations in a Shelf application


Non compliant code

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

void main() {
var handler = const shelf.Pipeline().addMiddleware(shelf.logRequests())

io.serve(handler, 'localhost', 8080);

shelf.Response _echoRequest(shelf.Request request) {
var user = request.url.queryParameters['user'];
return new shelf.Response.ok('User: $user');

The above code represents a Dart backend application using the Shelf framework. The main function sets up a server that listens on localhost at port 8080. The server is configured to log all requests and handle them using the _echoRequest function.

The _echoRequest function is where the vulnerability lies. This function takes the incoming request and extracts the 'user' parameter from the URL query parameters. It then returns this information in the response.

This is vulnerable to Automatic Information Enumeration, as it allows anyone to view the user data by simply sending a request with the appropriate 'user' parameter. Since there is no token or authentication mechanism in place to verify the identity of the requestor, this can lead to unauthorized access to other users' data.


  • Implement authentication middleware to verify the identity of the user making the request.
  • Use tokens (like JWT) to authenticate users. The token should be sent with each request and validated on the server.
  • Ensure that the token is associated with the account and is used to consult the information.
  • Restrict access to user information based on the authenticated user's permissions. Only allow users to access their own information.
  • Encrypt sensitive data to add an extra layer of security.
  • Implement rate limiting to prevent brute force attacks.

Compliant code

import 'dart:convert';
import 'package:shelf/shelf.dart' as shelf;
import 'package:shelf_auth/shelf_auth.dart';
import 'package:shelf/shelf_io.dart' as io;
import 'package:jaguar_jwt/jaguar_jwt.dart';

const String secret = 'secret';

void main() {
var handler = const shelf.Pipeline()
.addMiddleware(authenticate([new JwtAuthMiddleware(secret)]))

io.serve(handler, 'localhost', 8080);

shelf.Response _echoRequest(shelf.Request request) {
var user = request.context['auth'] as Map<String, dynamic>;
var userId = user['id'];
return new shelf.Response.ok('User: $userId');

Middleware authenticate(List<Authenticator> authenticators) {
return (shelf.Handler innerHandler) {
return (shelf.Request request) async {
for (var authenticator in authenticators) {
var authedRequest = await authenticator.authenticate(request);
if (authedRequest != null) {
return innerHandler(authedRequest);
return new shelf.Response.forbidden('Forbidden');

class JwtAuthMiddleware extends Authenticator {
final String secret;


Future<shelf.Request> authenticate(shelf.Request request) async {
var authHeader = request.headers['authorization'];
if (authHeader != null && authHeader.startsWith('Bearer ')) {
var jwtToken = authHeader.substring(7);
var claimSet = verifyJwtHS256Signature(jwtToken, secret);
var userId = claimSet.subject;
return request.change(context: {'auth': {'id': userId}});
return null;

The updated code now includes an authentication middleware that uses JWT (JSON Web Tokens) for user authentication. The authenticate function is a middleware that checks if the request has a valid JWT in the Authorization header. If the JWT is valid, it adds the user's ID to the request context and passes the request to the next middleware or handler. If the JWT is not valid or not present, it returns a 403 Forbidden response.

The JwtAuthMiddleware class is an Authenticator that verifies the JWT and extracts the user's ID from it. The authenticate method of this class is called for each request. If the Authorization header is present and contains a valid JWT, it verifies the JWT, extracts the user's ID from it, and adds it to the request context. If the JWT is not valid, it returns null, which causes the authenticate middleware to return a 403 Forbidden response.

The _echoRequest handler now gets the user's ID from the request context instead of the query parameters. This ensures that the user can only access their own information.

This code also uses the shelf_auth and jaguar_jwt packages for JWT authentication. The shelf_auth package provides the Authenticator interface and the authenticate middleware. The jaguar_jwt package provides functions for creating and verifying JWTs.

This code fixes the vulnerability by ensuring that only authenticated users can access user information, and that they can only access their own information. It also provides an extra layer of security by using JWTs, which are encrypted and signed, for authentication.