Hi Hackers 🙂

While testing a live application recently, I stumbled upon a security misconfiguration that’s not commonly seen in most web applications — yet it’s highly impactful if discovered.

What makes this finding interesting is that it revolves around GraphQL, a technology that’s increasingly being adopted but often misunderstood or misconfigured in production environments.

This isn’t your usual XSS or IDOR. It’s a subtle flaw that might not stand out at first glance — but when you understand the root cause, you’ll see why it deserves a spot in your bug bounty or VDP checklist.

If you’re actively participating in:

• 🛡️ Bug Bounty Programs (BBPs)
• 🔐 Vulnerability Disclosure Programs (VDPs)
• 👨‍💻 Private Pentesting Engagements

…this is something you’ll want to test for.

But before we dive deep into the actual vulnerability and its potential impact, let’s first build a solid understanding of GraphQL, how it works, and why it can be dangerous when misconfigured.

Stay tuned — you might end up adding a new test case to your recon flow by the end of this post. 😉

What is GraphQL

GraphQL is a query language that replaces traditional APIs like REST. It lets frontend applications request or update exactly the data they need from the backend. These requests are handled by the GraphQL server, which acts as a bridge between the client and the database.

Why GraphQL

Before GraphQL, web applications commonly faced the problem of over-fetching or under-fetching data when using traditional APIs like REST.

With GraphQL, an application can request exactly the data it needs — no more, no less. This ensures that the client receives only the necessary information to process the request, avoiding unnecessary data transfer or multiple round trips to the server.

🟠 Scenario 1 — Without GraphQL (Traditional REST API)

A user wants to update just their address on their profile.

• The frontend sends a PUT request to:

PUT /api/user/998387484

The request body may include the entire user object, such as:

{
 “name”: “John”,
 “email”: “john@example.com”,
 “address”: “New Address”,
 “phone”: “1234567890”
 }

• Even though only the address is changing, the entire object is sent.

🔍 Problem: This leads to over-fetching and over-posting (i.e., sending/receiving more data than necessary), and it depends on how the backend handles partial updates.

🟢 Scenario 2 — With GraphQL

The user wants to update only their address.

The frontend sends a mutation like:

mutation {
 updateAddress(userId: “998387484”, newAddress: “New Address”) {
 success
 message
 }
}

This is sent via a single endpoint:

POST /graphql

🔍 Advantage: The client specifies exactly what to update. No need to send the entire user profile — GraphQL handles fine-grained operations efficiently.

Why It’s Beneficial

• Reduced Payload Size: GraphQL reduces the amount of data transferred by allowing clients to request only the specific fields they need, minimizing unnecessary data.
• Fewer Requests: Unlike REST, where you might need to call multiple endpoints, GraphQL allows fetching data from multiple resources in a single request. This improves performance, especially for mobile and low-bandwidth environments.
• Fine-Grained Access Control: When configured properly, GraphQL is secure. It allows precise control over who can access what data, down to the field and operation level, making it easier to enforce security policies.

One liner for GraphQL

GraphQL is beneficial because it sends only the data you ask for (saving bandwidth), lets you get everything in one request (faster), and can be made secure with strict access control settings.

When the risk arises?

When a user tries to create, modify, or access data, GraphQL sends a query or mutation to the backend server via a single GraphQL endpoint.

• Query: Sent by the client to the server when fetching or reading data.
• Mutation: Sent by the client to the server when creating, modifying, or deleting data.

These endpoint are where the GraphQL server is set up to receive and handle requests, allowing the client to fetch or update only the necessary data :

/graphql
/api/graphql
/v1/graphql
/graphql-api
/data/graphql
/graphql-endpoint
/query
/graphql-service=

this is how a simple mutation request look like.

• If you pay close attention, you’ll notice that the response in GraphQL is completely driven by the client’s query.
• The client specifies exactly what data it wants — such as an id, email, or username — and the server simply fetches and returns that data, assuming the schema and resolvers allow it.

This opens up an interesting attack surface.

Since clients control the query, an attacker can manually craft a GraphQL query to try and fetch another user’s data — just by changing an id or username in the request.

If the GraphQL backend is misconfigured or lacks proper access control (especially at the object level), it may return data it shouldn’t — even for unauthorized users.

This is a classic case of IDOR (Insecure Direct Object Reference), more specifically known as BOLA (Broken Object Level Authorization) in the OWASP API Top 10.

🧠 What Can You Get?

In real-world scenarios, this could lead to:

• Exposing other users’ personal details (name, email, phone)
• Accessing internal resources
• Dumping sensitive information like passwords, tokens, or roles (if not filtered)

🛠️ Crafting Your Own Queries

Before we can create any meaningful GraphQL query to access data, we first need to understand the structure of the schema used by the application.

This includes knowing:

• What types are available
• What fields exist within those types
• What data types (e.g., String, ID, Int) are assigned to each field
• And whether certain types expose sensitive objects like User, Admin, or Password

Remember — GraphQL is flexible by design, and its structure varies from application to application. There is no fixed path or endpoint like in REST.

To reveal the internal structure of the GraphQL API, we can send a basic introspection query like this:

{
  __schema {
    types {
      name
      fields {
        name
      }
    }
  }
}

🔐 Introspection: A Double-Edged Sword

The introspection query mentioned earlier will only work if the GraphQL server has introspection enabled — which is often the case in development environments.

However, if introspection is disabled (as it should be in production), the server will reject such queries and not return any schema information.

❗ Best Practice: Disabling introspection in production environments is a widely recommended security measure. It prevents attackers from easily discovering the API structure and crafting targeted queries.

So if your introspection query fails — that’s actually a good sign from a security standpoint. But if it succeeds, you may have found a potential misconfiguration worth digging into.

Now that you’ve confirmed introspection is enabled, you’re in a powerful position. You can start crafting custom queries based on the schema to enumerate objects, dig deeper into nested fields, and — if misconfigured — even access sensitive PII (Personally Identifiable Information).

This is where real vulnerabilities begin to surface.

From here, you can:

• Try changing user identifiers to exploit IDORs (BOLA)
• Access unauthorized user data
• Query sensitive fields like email, password, token, or role
• Combine this with broken access controls for critical data exposure

Here’s a detailed introspection query I used to enumerate types and their fields:

🛡️ Introspection ≠ Vulnerability

Just because introspection is enabled doesn’t mean the application is vulnerable.

Introspection simply reveals the structure of the GraphQL schema — such as available types, queries, and fields. It does not mean you’re automatically able to access sensitive data.

In many cases, even if introspection is turned on, the GraphQL backend may be tightly coupled with user sessions and proper access control. This means:

• You can only fetch your own data (based on the authenticated user)
• Querying other users’ data will either return nothing or throw an access error

How Secure Introspection Looks

• It only fetches the data of the user I’m currently logged in as.

🔍 Always Enumerate Cautiously

If you’re able to retrieve other users’ data, such as their emails, tokens, or roles — this is a serious BOLA (IDOR) vulnerability and can be critical.

But if the schema is exposed via introspection but you’re not able to retrieve unauthorized data, it’s more of a low to medium severity issue. Still, it’s worth reporting, especially in programs that value secure configuration.

If you want to dive deeper into how to enumerate, exploit, and secure GraphQL endpoints, check out my detailed walkthrough on YouTube:

I cover everything from introspection to crafting custom queries, IDOR exploitation, and real-world attack scenarios. Perfect for bug bounty hunters, pentesters, and curious hackers. 🚀

Happy Hacking!

LinedIn : https://www.linkedin.com/in/raman-gautam-98208820a/

Youtube : https://www.youtube.com/@theunixverse77

Remember — GraphQL is flexible by design, and its structure varies from application to application. There is no fixed path or endpoint like in REST.