GraphQLer: Enhancing GraphQL Security with Context-Aware API Testing

GraphQL APIs power production systems across financial services, e-commerce, and social platforms, yet their most critical access-control vulnerabilities--Insecure Direct Object Reference (IDOR), Use-After-Free (UAF), and state-dependent injection--routinely escape automated security testing. Industry-standard scanners (ZAP) and the leading research fuzzer (EvoMaster) test operations in isolation and cannot compose the multi-step sequences these flaws require. We present GraphQLer, an open-source automated security testing framework built for production GraphQL APIs. GraphQLer constructs a typed dependency graph from live schema introspection and synthesizes vulnerability chains--ordered operation sequences targeting specific flaw classes. Three strategies cover the critical attack surface: topological SCC-traversal for general reachability, cross-user IDOR replay for broken access control, and CREATE -> DELETE -> READ synthesis for UAF. On a production financial API (FinServ), GraphQLer identified eight potential vulnerabilities--including denial-of-service vectors that exposed stack traces and sensitive implementation details--without prior documentation or authentication credentials. On a self-hosted Saleor instance pinned to the CVE-2022-39275 commit, GraphQLer reproduced all four broken-access-control mutations cited in the security advisory. On the 11 public APIs of the coverage set, GraphQLer achieves 85.52% mean PositiveCoverage versus 29.29% (EvoMaster) and 21.80% (ZAP); across the 21 evaluated APIs it detects all 5 confirmed IDOR endpoints, UAF behavior on two controlled schemas, and confirms XSS and SQLi on DVGA (an independent third-party oracle)--while all baselines detect zero chain-based vulnerabilities.