Authentication tells the API who you are.

Authorization defines what you’re allowed to do.

And in GraphQL, that second layer is frequently neglected — especially at the field and object level.

This post demonstrates how to reproduce and detect authorization bypass vulnerabilities in GraphQL APIs.

1. What Makes GraphQL Authorization Fragile?

Unlike REST, GraphQL allows a single request to query multiple resources and fields.

If the server doesn’t enforce per-field or per-object authorization checks, attackers can craft queries like:

query {
  users {
    id
    email
    isAdmin
    passwordHash
  }
}

Even if the endpoint is authenticated, the lack of granular access control leads to overexposure.

2. Reproducing Bypass Scenarios

Scenario A: Horizontal Privilege Escalation 

query {
  getUser(id: "1234") {
    id
    email
    billingInfo
  }
}

Now try:

getUser(id: "1235") // Not your own account

If the server returns the data: authorization check is missing.

Scenario B: Role-Based Bypass

Send request as a low-privilege user, but attempt to access:

mutation {
  createAdminUser(input: { username: "attacker", password: "1234" })
}

If no RBAC is applied to that resolver → direct privilege escalation.

3. Field-Level Exposure

Common mistake: exposing sensitive fields on shared objects without role checks.

query {
  me {
    id
    email
    jwtToken  // should be hidden
  }
}

Also common: fields only used for internal admin dashboards being exposed to regular users.

4. Detection Techniques

Manual Recon with Introspection

Use introspection to enumerate fields:

query {
  __type(name: "User") {
    fields {
      name
      type { name kind }
    }
  }
}

Look for suspicious fields:

  • isRoot, paymentToken, sessionSecret, logs

Fuzzing with Burp GraphQL Raider or Intruder

Automate the injection of:

  • Other user IDs
  • Unauthorized mutations
  • Role-altering fields

Track response differences:

  • Status codes
  • Length variations
  • Leaked values

Differential Testing

Compare same query results:

  • As normal user vs admin
  • As user A vs user B

If response differences are inconsistent with roles, authZ is flawed.

5. Logging + Rate Observability (Defensive Tip)

If you’re defending a GraphQL API:

  • Instrument resolvers with audit logs per field
  • Use contextual authZ: if (user.id !== targetUser.id) { deny }
  • Reject introspection in production unless whitelisted
  • Define schema-based access policies (e.g., with Hasura, GraphQL Shield)

Final Thoughts

GraphQL makes it easy to over-fetch.

Without strict per-resolver authorization, attackers will explore beyond their boundary — and often succeed.

In the next article, we’ll demonstrate:

  • Using GraphQL Shield to enforce RBAC
  • Mock exploit labs for field-level overreach

Test the edges. Validate the rules. Never trust the schema alone.