How a GraphQL Bug Resulted in Authentication Bypass

This report details a GraphQL-based authentication bypass discovered in a third-party integration for an e-commerce site's promotional banner: enabled introspection exposed registration and privileged mutations (e.g., CreateAdminUser), allowing unauthenticated account creation and potential admin escalation. The piece explains how attackers enumerate GraphQL schemas, common weaknesses (field-level authorization gaps, complex schemas, introspection), possible business impacts (fraud, PII theft, defacement), and recommended mitigations such as disabling introspection in production, strict per-query/mutation authorization, removing unnecessary functionality, and using anti-bot verification for registration flows. The vulnerability was responsibly reported through HackerOne and fixed.