What Is API Security Testing? (And Why It’s Now Critical)
APIs power modern applications and integrations — and they are now the most attacked part of most platforms. API security testing finds the authorisation and logic flaws that scanners consistently miss. Here is what it involves.
Key takeaways
- APIs expose business logic and data directly, which makes authorisation flaws especially damaging.
- Broken Object Level Authorisation (BOLA/IDOR) is the number one API risk and requires manual testing to find.
- Automated tools miss most serious API issues — depth comes from human testing against real accounts and roles.
- API testing should cover REST, GraphQL and SOAP, plus the authentication and rate-limiting around them.
Why APIs are a prime target
Modern software is API-first. Your web and mobile apps, partner integrations and internal services all talk over APIs, and those APIs expose data and functionality directly. That directness is the problem: where a web page might hide a button, an API endpoint simply accepts the request — so a single missing authorisation check can leak every customer’s record.
Attackers have noticed. APIs are now among the most targeted parts of any platform, and the flaws that hurt most are rarely the ones scanners catch.
The OWASP API Security Top 10
API testing is structured around the OWASP API Security Top 10, which reflects how APIs actually fail. Top of the list is Broken Object Level Authorisation (BOLA, also called IDOR) — where changing an identifier lets one user access another’s data. Close behind are broken authentication, broken function-level authorisation (admin actions exposed to normal users), mass assignment, and excessive data exposure.
These are authorisation and logic problems, not simple bugs. Finding them reliably means testing with real accounts across different roles and tenants, which is exactly what automated tools cannot do.
What a good API assessment covers
A thorough API VAPT ingests your OpenAPI/Swagger definition (or discovers endpoints), analyses authentication and token handling (JWT, OAuth 2.0), and systematically tests authorisation across every object and function. It probes for injection, SSRF, rate-limiting gaps and business-logic abuse, and — for GraphQL — introspection, batching and deep-query issues.
Every finding is verified by chaining it into real impact, rated by business risk, and delivered with developer-ready remediation and a free re-test.
Getting the most from testing
Provide test accounts across roles and tenants so testers can properly probe authorisation boundaries. Share API documentation to maximise coverage. And treat API testing as ongoing rather than one-off, since APIs change constantly with each release.
Frequently asked questions
What is BOLA and why does it matter so much?+
Broken Object Level Authorisation is when an API lets a user access another user’s data by changing an identifier. It is the most common and highest-impact API vulnerability, and reliably finding it requires manual testing with multiple accounts.
Do you test GraphQL and SOAP as well as REST?+
Yes. Each is tested with an approach tailored to it — for example introspection, batching and deep-query abuse for GraphQL, and operation and schema review for SOAP.
Do you need our API documentation?+
It helps us go deeper faster, but it is not mandatory — we can discover and enumerate endpoints ourselves if documentation is not available.
Put this into practice
Get a free, no-obligation security assessment, or talk to a senior Aesparrow practitioner about your goals.