APIs power modern enterprise applications — connecting frontend and backend systems, enabling integrations, and exposing business functionality to partners and mobile apps. They are also the primary attack surface of modern software. API security testing requires a different approach from web application testing.
Why APIs Are Different
Traditional web application testing focuses on the user interface — forms, pages, and browser-based interactions. API testing operates at the protocol level, testing the endpoints and data contracts that applications rely on. APIs often expose more functionality than the user interface does, creating a broader attack surface. They may accept structured data (JSON, XML, GraphQL queries) that introduces different injection and manipulation risks.
The OWASP API Security Top 10
The OWASP API Security Top 10 provides the industry framework. Key categories include:
**Broken Object Level Authorization (BOLA)** — the most common critical API vulnerability. Can User A access User B's data by manipulating object IDs? Automated tools struggle with this because they don't understand which objects belong to which users.
**Broken Authentication** — weaknesses in API authentication mechanisms, including token handling, credential rotation, and multi-factor implementation.
**Broken Object Property Level Authorization** — can a user read or modify object properties they shouldn't have access to?
**Unrestricted Resource Consumption** — can an attacker abuse API endpoints to consume excessive resources?
**Broken Function Level Authorization** — can a regular user invoke administrative API functions?
**Server-Side Request Forgery (SSRF)** — can an attacker make the server issue requests to internal resources?
**Security Misconfiguration** — default configurations, unnecessary HTTP methods, overly permissive CORS policies.
**Lack of Protection from Automated Threats** — can API functionality be abused at scale through automated requests?
Why Manual Testing Is Essential for APIs
The most critical API vulnerabilities — BOLA, BFLA, business-logic abuse — are authorisation flaws that require understanding of the intended access model. No automated tool can determine whether a specific API response should be accessible to a specific user, because that determination requires business-context understanding. Expert testers map the authorisation model and systematically test every endpoint with every role.
How Simuna Infosec Tests APIs
We test REST, GraphQL, and SOAP APIs against the full OWASP API Security Top 10, with additional custom testing for payment and transaction APIs where business-logic abuse carries direct financial impact. Our BSS and telecom API testing experience gives us deep familiarity with the authorisation patterns that matter most in complex, multi-role systems.