Graphql Introspection in Buffalo

GraphQL introspection is a built-in feature that allows clients to query the schema for information about types, fields, and operations. While essential during development, leaving introspection enabled in production exposes your API's entire data structure to unauthenticated attackers. In Buffalo applications that serve GraphQL endpoints—typically via third-party libraries like github.com/99designs/gqlgen or github.com/graphql-go/graphql—this vulnerability arises when the GraphQL handler is configured without restricting introspection.

Attackers exploit this by sending an introspection query such as:

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

This returns the complete schema, revealing type names, field names, and nested relationships. In a Buffalo app, the GraphQL endpoint is usually mounted in routes.go or via a separate action. If the GraphQL library's configuration does not explicitly disable introspection (e.g., DisableIntrospection: true in gqlgen), the endpoint remains vulnerable. This information disclosure aids attackers in mapping the API for targeted exploits like BOLA/IDOR or excessive data extraction.

To detect GraphQL introspection in a Buffalo application, first identify the GraphQL route. Common patterns include:

• Routes defined in routes.go: app.GET("/graphql", graphqlHandler)
• Actions that serve GraphQL: func (v GraphQLResource) GraphQL(c buffalo.Context) error { ... }

Manually, you can test by sending an introspection query to the endpoint with a tool like curl:

curl -X POST http://your-app.com/graphql \
  -H 'Content-Type: application/json' \
  -d '{"query": "{ __schema { types { name } } }"}'

If the response includes a data.__schema.types array, introspection is enabled.

middleBrick automates this detection. When you scan your Buffalo API URL, middleBrick identifies GraphQL endpoints and tests for introspection as part of its Data Exposure check. If the full schema is retrievable, it generates a high-severity finding with the exact query used and the exposed schema snippet. The scanner also cross-references any OpenAPI/Swagger spec (if provided) to highlight discrepancies between documented and runtime schema exposure.

Remediation requires disabling introspection in the GraphQL server configuration. The implementation depends on the GraphQL library used. Below are examples for two common Go GraphQL libraries integrated with Buffalo.

Using gqlgen (most common): In your Buffalo route setup (routes.go or a dedicated initializer), configure the handler with DisableIntrospection: true for production environments:

package routes

import (
  "os"
  "github.com/gobuffalo/buffalo"
  "github.com/99designs/gqlgen/graphql/handler"
  "github.com/yourproject/graph" // generated gqlgen schema
)

func init() {
  // ... other routes

  // Disable introspection in production
  disableIntrospection := os.Getenv("ENV") == "production"

  gqlHandler := handler.New(&handler.Config{
    Schema: graph.NewExecutableSchema(graph.Config{Resolvers: &graph.Resolver{}}),
    DisableIntrospection: disableIntrospection,
    // ... other config (e.g., complexity, validation)
  })

  app.GET("/graphql", buffalo.Wrap(gqlHandler))
}

Using graphql-go: Set the Introspection field to false when creating the http.Handler:

import "github.com/graphql-go/graphql"

schema, _ := graphql.NewSchema(graphql.SchemaConfig{ ... })

handler := &graphql.Handler{
  Schema: schema,
  Introspection: false, // disable introspection
}

app.GET("/graphql", buffalo.Wrap(handler))

Always conditionally disable introspection (e.g., only in production) to retain development flexibility. After applying the fix, re-scan with middleBrick to verify the introspection query now returns an error or empty response. Note that Buffalo itself does not provide GraphQL utilities—these configurations are specific to the underlying GraphQL library you've integrated.