Broken Authentication in Chi with Dynamodb

Broken Authentication in a Chi application that uses Dynamodb often stems from how session or credential data is modeled and validated against the database. When authentication state or user credentials are stored in Dynamodb without adequate safeguards, the API surface exposed by Chi routes can lead to authentication bypass or credential leakage.

Chi routes typically match requests and call business logic that reads or writes user data from Dynamodb. If these routes do not enforce strict authentication checks—for example, missing route guards or relying solely on client-supplied identifiers—an attacker can manipulate identifiers or tokens to access another user’s data. This maps to the OWASP Authentication Broken Authentication category and commonly appears as IDOR when object references in Dynamodb are predictable.

A realistic pattern in Chi is to retrieve a user record by a path parameter such as user_id. If the route does not verify that the authenticated subject matches the requested user_id, an unauthenticated or low-privilege user can enumerate or modify other accounts. Even when JWTs are used, if the validation logic does not properly scope tokens to the correct partition key in Dynamodb, token replay or substitution can occur.

Dynamodb’s schema flexibility can inadvertently contribute to the problem. For instance, storing sensitive attributes like password hashes or session flags in top-level attributes without proper access control can expose them if a query or scan is misconfigured. Insecure default permissions in table policies or misconfigured IAM roles used by the service can allow read or write access that should be restricted, enabling vertical or horizontal privilege escalation across user boundaries.

Consider a Chi endpoint that updates user profile information by primary key without confirming ownership. If the endpoint trusts a client-supplied key and directly forwards it to Dynamodb, this becomes a BOLA (Broken Level of Authorization) vector. Attackers can iterate through valid keys to access or alter data belonging to other users. This is especially risky when the primary key is a predictable attribute like a numeric user ID or email prefix.

middleBrick can detect these risks by scanning the unauthenticated attack surface of a Chi + Dynamodb API, including OpenAPI specs if provided. It runs checks across Authentication, BOLA/IDOR, and Property Authorization, correlating spec definitions with runtime behavior. The scanner identifies places where authentication checks are missing or misaligned with data access patterns, providing prioritized findings with severity and remediation guidance mapped to frameworks such as OWASP API Top 10.

Remediation focuses on ensuring that every data access path in Chi validates the authenticated subject against the Dynamodb key and enforces least-privilege data access. Below are concrete, secure patterns for Chi routes using the official AWS SDK for Dart.

First, always derive the partition key from the authenticated user’s identity rather than trusting client input. Use Chi’s request extensions to pass the authenticated subject into handlers, and construct Dynamodb queries that filter by this subject.

import 'package:aws_sdk/dynamodb.dart';
import 'package:chi/chi.dart';
import 'package:http/http.dart' as http;

// Assume request extension provides the authenticated user ID
extension on Request {
  String get userId => context['userId'] as String;
}

Future<void> updateUserProfile(HandlerContext context) async {
  final request = context.request;
  final userId = request.userId; // authenticated subject from JWT/session
  final body = await request.readAsString();
  final payload = json.decode(body) as Map;

  final client = DynamoDbClient(region: 'us-east-1');
  try {
    final result = await client.updateItem(
      tableName: 'users',
      key: {'userId': AttributeValue(s: userId)},
      updateExpression: 'SET #email = :email, #name = :name',
      expressionAttributeNames: {
        '#email': 'email',
        '#name': 'name',
      },
      expressionAttributeValues: {
        ':email': AttributeValue(s: payload['email']),
        ':name': AttributeValue(s: payload['name']),
      },
    );
    context.response = Response.ok(json.encode({'updated': result}));
  } finally {
    await client.close();
  }
}

This pattern ensures the update targets only the authenticated user’s item by using the authenticated subject as the partition key. It avoids using any client-supplied identifier as the key, which prevents IDOR-style manipulation.

Second, enforce attribute-level authorization when reading or writing sensitive fields. Do not rely on client-provided flags or roles stored in Dynamodb; instead, compute permissions based on the authenticated subject and a strict allowlist on the server.

Future<bool> canAccessSensitiveData(String userId, String targetUserId) async {
  // Only allow access if the requesting subject matches the target
  return userId == targetUserId;
}

Third, apply least-privilege IAM policies to the service role used by Chi. Grant only the specific actions needed (e.g., dynamodb:GetItem, dynamodb:UpdateItem) on the exact table and key condition that align with the authenticated subject. Avoid wildcard actions or resource ARNs that permit broad scanning.

With these changes, the Chi + Dynamodb stack reduces the risk of broken authentication by tying data access directly to verified identities, validating input, and limiting authorization checks to server-side logic. middleBrick’s scans can then verify that these controls are reflected in the API surface by analyzing the spec and runtime findings for Authentication, BOLA/IDOR, and Property Authorization issues.

For ongoing assurance, use the middleBrick CLI to scan from the terminal with middlebrick scan <url>, or integrate the GitHub Action to fail builds if the security score drops below your chosen threshold. The Pro plan adds continuous monitoring and CI/CD pipeline gates, while the MCP Server lets you scan APIs directly from your AI coding assistant within the Chi project.