API Security
REST, GraphQL & SOAP API Security Testing
Targeted testing of your API attack surface — OWASP API Top 10 and beyond.
What is API Security?
APIs are the backbone of modern applications — and increasingly, the primary target for sophisticated attackers. Unlike web application vulnerabilities that often affect single endpoints, API vulnerabilities can expose the entire data layer behind an application. Broken Object Level Authorisation (BOLA), the most common API vulnerability, allows attackers to access any user's data by manipulating object identifiers.
Our API Security service tests your REST, GraphQL, and SOAP APIs against the OWASP API Security Top 10 (2023), with deep manual testing of authorisation logic, input validation, rate limiting, schema enforcement, and injection surfaces. We test from multiple privilege tiers — unauthenticated, standard user, and where applicable, admin-level — to understand the complete access control picture.
For GraphQL APIs, we test for introspection exposure, batching attacks, deep query injection, and field-level authorisation bypass — a category of vulnerabilities that standard REST testing methodologies miss entirely.
Why it matters
- OWASP ranks Broken Object Level Authorisation as the #1 API risk — it's trivial to exploit and exposes entire datasets
- API endpoints are often less protected than web endpoints — they're designed for machine consumption and frequently skip human-readable security controls
- Mobile and web frontends share API backends — a single API vulnerability compromises all clients simultaneously
- Internal APIs exposed via API gateways often have weaker authorisation than external ones, creating lateral movement opportunities
- Excessive data exposure — APIs returning full objects when only a field is needed — is endemic and routinely leads to mass data leaks
Our methodology
1. API Discovery & Documentation Review
Collection of all API specifications (OpenAPI/Swagger, GraphQL schema, WSDL), supplemented by traffic capture and directory brute-forcing to discover undocumented endpoints. We identify every input parameter and auth mechanism before testing begins.
2. Authorisation & Authentication Testing
Testing BOLA, Broken Function Level Authorisation (BFLA), and broken authentication across all privilege tiers. We probe whether horizontal and vertical privilege escalation is possible via parameter manipulation and token reuse.
3. Input Validation & Injection Testing
All input parameters tested for injection (SQL, NoSQL, command, SSTI, XXE), mass assignment, and type confusion. Rate limiting and quota enforcement tested for abuse scenarios.
4. Business Logic & Abuse Scenario Testing
Manual testing of API workflows for multi-step business logic vulnerabilities — race conditions in transaction processing, workflow bypass, resource exhaustion, and replay attack susceptibility.
Frequently asked questions
Do you need our API documentation to start?
Documentation helps significantly but isn't mandatory. We can discover APIs by capturing application traffic, analysing JavaScript bundles, and directory enumeration. If you have OpenAPI/Swagger specs, sharing them allows us to provide faster and more comprehensive coverage.
Can you test internal APIs that aren't publicly exposed?
Yes. Internal API testing is conducted from an agreed network position (e.g., via VPN to your internal network) and is particularly valuable — internal APIs are often less hardened because they're assumed to be trusted.
How do you test GraphQL without exposing introspection?
We test for introspection exposure as part of the engagement, but even when introspection is disabled, we use field-name enumeration, clairvoyance tooling, and manual schema inference to map the schema. Disabling introspection alone is not a security control.
What's the difference between API Security testing and web application testing?
Web application testing focuses on the rendered HTML/JS interface. API security testing focuses on the machine-to-machine interface — different endpoints, different authentication patterns (OAuth, JWT, API keys), and different vulnerability classes (BOLA, mass assignment, schema injection) that don't apply to web UI testing.
We use an API gateway — does that reduce our risk?
API gateways help with rate limiting and basic authentication, but they don't protect against BOLA (the most common API vulnerability), business logic flaws, or authorisation mismatches between the gateway policy and the backend microservice. Testing both the gateway and backend directly is essential.
Deliverables
OWASP API Top 10 Mapping
Every finding mapped to the OWASP API Security Top 10 (2023) categories
Annotated API Specification
Your OpenAPI/Swagger or GraphQL schema annotated with security findings
Postman / Burp Collection
All test requests and PoC payloads packaged for your team to reproduce findings
Authorisation Matrix
Tested privilege matrix showing which tiers can access which resources
Technical Report with PoC
Full finding detail with request/response captures and CVSS scores
Retest Report
Post-fix verification of all critical and high findings
Industries served
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All engagements are led by certified operators with unlimited retests until every critical finding is resolved.