Graphql Introspection Abuse in Aspnet (Csharp)

GraphQL introspection abuse in an ASP.NET application using C# occurs when an attacker can query the GraphQL schema to discover types, queries, and operations that should remain internal. In ASP.NET, this typically arises when the GraphQL endpoint is exposed without restricting introspection queries, allowing an unauthenticated attacker to map the API surface. Because GraphQL responses include type definitions, argument descriptions, and resolver logic, an attacker can infer authentication requirements, data relationships, and potential injection points. The C# implementation often exposes introspection by default, especially when using libraries like GraphQL.Server.Transports.AspNetCore or HotChocolate without explicit schema filtering. When combined with unauthenticated scanning by middleBrick, which runs 12 parallel security checks including BOLA/IDOR and Input Validation, the introspection endpoint can reveal sensitive field structures and operation names. This enables attackers to craft precise BOLA/IDOR probes or SSRF payloads that target specific resolvers. The risk is amplified when the schema includes queries that expose user data or administrative operations, as introspection provides a blueprint for exploitation. Because middleBrick tests unauthenticated attack surfaces, it can detect whether introspection is permitted and enumerate the full schema in seconds. This information can be used to plan further attacks such as privilege escalation via BFLA or data exposure through overly permissive queries. The C# stack may also lack rate limiting on introspection, allowing enumeration at scale. Introspection queries themselves are valid GraphQL operations, so traditional network controls like IP blocking are less effective. Defense requires explicitly disabling introspection in production or enforcing strict query whitelisting. middleBrick’s GraphQL-specific analysis is part of its Input Validation and Inventory Management checks, highlighting whether introspection is reachable and whether sensitive types are exposed. Without mitigation, this becomes a foundational reconnaissance step in the API hacking chain.

To remediate GraphQL introspection abuse in ASP.NET with C#, explicitly disable introspection in production environments and apply schema filtering. Below are concrete code examples using HotChocolate and GraphQL.Server libraries.

1. Disable introspection in HotChocolate (C#)

using HotChocolate.AspNetCore;
using HotChocolate.Execution;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddGraphQLServer()
    .AddQueryType<Query>()
    .SetIntrospectionOptions(options =>
    {
        options.AllowIntrospection = false; // Disable introspection in production
    });

var app = builder.Build();
app.MapGraphQL();
app.Run();

2. Disable introspection in GraphQL.Server (C#)

using GraphQL;
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(options =>
        {
            options.EnableMetrics = false;
            options.ExposeExceptions = false;
        })
        .AddSystemTextJson()
        .AddGraphTypes(typeof(Startup).Assembly);
    

    
        // Disable introspection by not registering IntrospectionSchema
    }
    
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        app.UseWebSockets();
        app.UseGraphQL<Schema>();
        // Do not map /introspection endpoint
    }
    
}

3. Query validation to block introspection-like queries

using GraphQL.Validation;

public class NoIntrospectionRule : IValidationRule
{
    public ValueTask<INodeVisitor> ValidateAsync(DocumentValidationContext context)
    {
        return new ValueTask<INodeVisitor>(new NodeVisitor(
            new EnterLeaveListener(listener =>
            {
                listener.MatchOperation(op =>
                {
                    if (op.Name?.Value.Equals("__schema", StringComparison.Ordinal) == true ||
                        op.Name?.Value.Equals("__type", StringComparison.Ordinal) == true)
                    {
                        context.ReportError(new ValidationError(
                            context.OriginalQuery,
                            "Introspection queries are not allowed",
                            op));
                    }
                });
            })));
    }
}

// Register in HotChocolate:
builder.Services.AddGraphQLServer()
    .AddQueryType<Query>()
    .AddValidationRule<NoIntrospectionRule>();

4. Apply schema filtering to limit exposed types

using HotChocolate.Types.Descriptors;

public class SchemaFilterConvention : IConventionProvider
{
    public void Apply(IConventionDescriptor descriptor)
    {
        descriptor.BindClrType<UserType>()
            .Ignore(f => f.SensitiveDataField);
    }
}

// In registration:
builder.Services.AddGraphQLServer()
    .AddConvention<ISchemaFilter, SchemaFilterConvention>();

These C#-specific configurations ensure introspection is disabled or tightly controlled, reducing the attack surface that middleBrick would otherwise detect during its unauthenticated scan.