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Automated Security Protocol

How to fix Logic Flow Bypass
in Dart Frog

Executive Summary

Logic flow bypasses in Dart Frog typically occur when developers rely on client-side state or easily spoofed headers to manage authorization transitions. In these scenarios, an attacker can skip critical validation steps (like payment or MFA) by directly calling subsequent route handlers. To secure the flow, you must implement server-side state verification and use Dart Frog's RequestContext to inject validated principals.

The Vulnerable Pattern

VULNERABLE CODE
// routes/internal/export_data.dart
import 'package:dart_frog/dart_frog.dart';

Response onRequest(RequestContext context) {
// VULNERABILITY: Relying on a client-controlled header to bypass logic
final isVerified = context.request.headers[‘X-Step-Verified’] == ‘true’;


if (!isVerified) {
return Response(statusCode: 403, body: ‘Complete step 1 first’);
}


return Response(body: ‘Sensitive Data Exported’);
}

The Secure Implementation

The vulnerable code suffers from a logic bypass because it trusts the 'X-Step-Verified' header, which any attacker can inject. The secure implementation moves the logic into a Middleware layer that validates the session against a server-side 'SessionRepository'. By using 'context.provide', we ensure that the route handler only receives a 'User' object if the entire authentication and logic flow (like MFA) has been strictly validated on the server. This prevents attackers from 'jumping' into routes without satisfying the prerequisite state.

SECURE CODE
// middleware/auth_middleware.dart
Handler authMiddleware(Handler handler) {
  return (context) async {
    final session = await context.read().getCurrentSession();
    if (session == null || !session.hasCompletedMfa) {
      return Response(statusCode: 403);
    }
    return handler(context.provide(() => session.user));
  };
}

// routes/internal/export_data.dart
import ‘package:dart_frog/dart_frog.dart’;


Response onRequest(RequestContext context) {
// SECURE: Dependency injection of a validated User object
final user = context.read();


if (user.role != Role.admin) {
return Response(statusCode: 403);
}


return Response(body: ‘Sensitive Data Exported’);
}

System Alert • ID: 8377
Target: Dart Frog API
Potential Vulnerability

Your Dart Frog API might be exposed to Logic Flow Bypass

74% of Dart Frog apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.

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