API security testing finds weaknesses that attackers can exploit in your APIs. Common issues include broken authorisation, weak authentication, and excessive data exposure. Good testing starts with API discovery. It checks access controls, validates real exposure, and runs continuously as APIs change. This helps teams focus on weaknesses that attackers can actually use.
Why API security testing matters
APIs connect modern software. Applications, mobile apps, integrations, and cloud services all use APIs to exchange data and perform actions.
APIs often provide access to sensitive data and important functions. In some cases, they expose more than the user interface does.
This makes APIs a common target for attackers.
API security testing helps find weaknesses before attackers exploit them. It also differs from standard web application testing.
APIs have their own risks and attack patterns. They also operate at a large scale. Security testing must account for how APIs work and how attackers abuse them.
The risks API testing looks for
Good API security testing focuses on the risks that matter most. Many of these appear in the OWASP API Security Top 10.
Common examples include:
- Broken object-level authorisation: A user can access another user’s data by changing an object ID.
- Broken authentication: Weak login or token controls allow attackers to bypass authentication.
- Excessive data exposure: An API returns more information than the user needs.
- Lack of rate limiting: Attackers can send large numbers of requests without enough control.
- Broken function-level authorisation: A user can access functions that their account should not use.
Authorisation plays a major role in API security.
An API must check what each user can access and what each user can do. Testing must therefore examine these checks across the API.
Best practice: discover every API first
Start API security testing with discovery.
Many organisations have more APIs than they realise. These can include undocumented, forgotten, and shadow APIs.
Testing only documented APIs leaves these endpoints outside your testing process.
You cannot test what you do not know exists.
A current API inventory gives security teams a better starting point. It should include every API that an organisation exposes.
This requires more than a one-time inventory. APIs change often. New endpoints appear, old ones remain online, and teams may create APIs outside the normal development process.
Continuous API discovery helps keep the inventory current.
Best practice: test authorisation on every endpoint
Authorisation testing should cover every endpoint and object.
A user may have permission to access one resource but not another. The API needs to check that difference every time.
Testing should also check function-level access.
For example, a normal user may view an account but should not have access to administrative functions.
Attackers often test these boundaries. They may change an object ID, alter a request, or call a function that their account should not access.
One endpoint may enforce these checks correctly while another does not.
Systematic testing helps find these gaps across the API.
Best practice: validate, do not just scan
Scanners can find potential API weaknesses. They cannot always prove that an attacker can exploit them.
Validation answers that question.
A security tester can safely attempt the attack and confirm what the API allows.
For example, a scan may flag a possible authorisation problem. Validation can show whether one user can actually access another user’s data.
This distinction matters when teams decide what to fix first.
A long list of possible issues does not show which weaknesses create real exposure. Validation provides evidence about what an attacker can actually exploit.
It also reduces noise.
Instead of working through a long list of unconfirmed findings, teams can focus on weaknesses that testing has proven exploitable.
Best practice: test continuously
APIs change often.
Development teams add new endpoints, change existing functions, and release new API versions. Each change can introduce a new weakness.
A point-in-time test only shows the API as it existed when the test ran.
A clean result from last month does not prove that a new endpoint remains secure today.
Continuous testing keeps security checks aligned with these changes.
It re-tests the API as it evolves. This helps teams find new weaknesses sooner.
For organisations that release APIs often, continuous validation provides a more current view of security than occasional testing.
Turning testing into protection
Testing only reduces exposure when teams act on the results.
A useful API security process follows a clear cycle:
- Discover the APIs you expose.
- Test authentication, authorisation, and other controls.
- Validate weaknesses to confirm real exposure.
- Prioritise the issues that attackers can exploit.
- Fix the confirmed weaknesses.
- Retest to confirm the fix works.
This process turns security testing into an ongoing security practice.
The goal is not simply to produce a report. The goal is to make APIs harder for attackers to abuse.
To discover, test, and validate your APIs from an attacker perspective, explore our API security capability. You can also learn how continuous service validation keeps testing current as your APIs change.
For key API security risks, see the OWASP API Security Top 10.
Frequently asked questions
What is API security testing?
API security testing checks APIs for weaknesses that attackers could exploit. It covers areas such as authentication, authorisation, data access, rate limits, and exposed functions. Testing can combine automated scanning, manual testing, and validation.
What are the main API security risks?
Common risks include broken object-level authorisation, broken authentication, excessive data exposure, weak rate limiting, and broken function-level authorisation. These issues can allow attackers to access data or functions they should not reach.
Why discover APIs before testing?
Organisations often have undocumented, forgotten, and shadow APIs. If security teams do not know an API exists, they cannot test it. API discovery helps create a current view of the endpoints that need testing.
How often should you test APIs?
Test APIs continuously when they change often. New endpoints, features, and versions can introduce new weaknesses. Continuous validation checks the API as it evolves and helps teams find new exposure sooner.
Request an Attack Insights demo
See how Attack Insights helps security teams discover, assess, and validate external API exposure.
