Graphql Introspection in Aspnet with Firestore

GraphQL introspection exposes the schema of an API, which can reveal sensitive information about operations, types, and directives. In an ASP.NET environment using Firestore as the backend, enabling introspection in production can allow attackers to map the data model and query capabilities, aiding in reconnaissance for further attacks such as BOLA/IDOR or over-privileged queries. Firestore security rules often rely on structured paths and document fields; introspection may expose these structures, including how collections and documents are organized.

When GraphQL is implemented in ASP.NET with Firestore, introspection queries (like __schema { queryType { name } }) can return full type definitions, including custom scalars and object relationships. If the GraphQL server is unauthenticated or improperly constrained, an attacker can run these queries without credentials. Because Firestore rules are evaluated at query time, revealing the schema does not directly bypass rules, but it provides precise targeting vectors, such as identifying public read paths or misconfigured collection group rules.

In this stack, introspection can intersect with the 12 security checks run by middleBrick, particularly Input Validation, Property Authorization, and Unsafe Consumption. For example, an attacker might use introspection results to craft nested queries that stress Firestore read limits or attempt to access fields that should be restricted. middleBrick’s unauthenticated scan can detect whether introspection is exposed and highlight the associated risks, such as excessive agency through query complexity or potential data exposure via the GraphQL endpoint.

To secure GraphQL introspection in ASP.NET with Firestore, disable introspection in production and enforce strict query validation. Below are concrete code examples for an ASP.NET Core application using GraphQL.NET and the Google Cloud Firestore client.

First, configure the GraphQL endpoint to disable introspection in production environments. In Startup.cs or minimal API setup, conditionally enable introspection only in development:

using GraphQL.Server; 
using GraphQL.Server.Ui.Playground; 
using Microsoft.AspNetCore.Builder; 
using Microsoft.AspNetCore.Hosting; 
using Microsoft.Extensions.DependencyInjection;

public class Startup
{
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddGraphQL(b => b
                .AddSystemTextJson())
            .AddGraphTypes(typeof(MyQuery).Assembly)
            .AddDataLoader()
            .AddFirestoreStore(); // hypothetical extension for Firestore

        // Introspection disabled by default; enabled only in Development
        if (Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") == "Development")
        {
            services.AddGraphQLIntrospection();
        }
    }

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseGraphQLPlayground();
            app.UseGraphQLIntrospection();
        }
        app.UseGraphQL("/graphql");
    }
}

Second, secure Firestore access by using security rules that restrict collection and document access based on authentication and resource hierarchy. Even when introspection is disabled, ensure your GraphQL resolvers validate input against Firestore rules. Example Firestore security rules to limit public reads:

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /publicItems/{itemId} {
      allow read: if request.auth != null || false; // deny public by default
      allow write: if request.auth != null && request.auth.token.admin == true;
    }
    match /users/{userId} {
      allow read, write: if request.auth != null && request.auth.uid == userId;
    }
  }
}

Third, in your ASP.NET GraphQL resolvers, explicitly validate and sanitize inputs before querying Firestore. Use parameterized queries and avoid dynamic field selection that could be influenced by introspection output. Example resolver using Firestore client:

using Google.Cloud.Firestore;
using System.Threading.Tasks;

public class ItemTypeResolver
{
    private readonly FirestoreDb _firestore;
    public ItemTypeResolver(FirestoreDb firestore)
    {
        _firestore = firestore;
    }

    public async Task GetItemById(string itemId)
    {
        DocumentReference docRef = _firestore.Collection("items").Document(itemId);
        DocumentSnapshot snapshot = await docRef.GetSnapshotAsync();
        if (snapshot.Exists && snapshot.ContainsField("name"))
        {
            return new Item { Id = snapshot.Id, Name = snapshot.GetValue("name") };
        }
        return null;
    }
}

Finally, integrate middleBrick into your workflow: use the CLI (middlebrick scan <url>) or GitHub Action to detect if introspection remains exposed in staging. The Pro plan enables continuous monitoring and CI/CD pipeline gates to prevent regression, while the MCP Server allows scanning directly from IDEs during development. These scans complement secure coding practices by providing actionable findings aligned with frameworks like OWASP API Top 10.