API Security Testing
APIs are the connective layer behind modern applications. Test them as seriously as the applications they power.
Web and mobile front ends are increasingly thin. The logic, the data and the authorization decisions sit behind APIs — and those APIs are reachable directly, not only through the interface that was designed to call them.
That gap is the point. An attacker does not have to use your app the way your users do. They can call the endpoint directly, change an identifier, replay a request, or skip the step the interface would have enforced.
Each hop is a boundary. A boundary that is assumed rather than enforced is where API findings come from.
- CLIENTClientWeb, mobile or third-party consumerAuthentication boundary
- APIAPI layerRouting, tokens, rate limiting, input handlingAuthorization boundary
- SERVICESInternal servicesService-to-service calls and internal trustTrust boundary
- DATABASEDataRecords, tenancy separation, sensitive fields
Conceptual view. Real environments are assessed against the architecture you provide.
Focus areas
Why APIs need separate attention
Testing an application through its interface only exercises the requests the interface chooses to make. The API accepts far more than that — different parameters, different order, different identifiers, different roles.
Authorization is the recurring theme. Authentication is usually handled centrally and handled well. Authorization is decided per endpoint, often by different people at different times, and that is where the gaps appear.
How we test APIs
- 01INVENTORYEstablish which endpoints exist, including ones not in the documentation.
- 02ROLESMap callers, scopes and what each is meant to reach.
- 03BOUNDARYTest each boundary directly rather than through the front end.
- 04LOGICWork sequences, state and multi-step operations.
- 05VALIDATEReproduce findings cleanly and capture evidence.
- 06REPORTSeverity, affected endpoints and remediation guidance.
A report your team can actually act on.
Exact deliverables and their format are confirmed during scoping.
What was assessed, what was found and what it means, written to be read by people who will not read the technical detail.
Each finding described with enough precision for an engineer to locate and understand it.
Reproduction detail and supporting evidence, so findings can be verified rather than taken on trust.
Severity considered against your environment, not only against a generic scoring table.
Practical direction on addressing each finding, including where a change belongs architecturally.
Verification that addressed findings no longer reproduce, within the agreed retest scope.
Organizations this typically applies to.
Testing is scoped per engagement. Nothing here implies industry-specific certification or accreditation.
When Do APIs Need Testing on Their Own?
Adjacent parts of the attack surface.
Questions we get asked before an engagement.
Both, along with other request/response styles. GraphQL shifts some risk — introspection, query depth and field-level authorization become more prominent — but the underlying questions about who may reach which object are the same.
It helps and speeds things up, but it is not a prerequisite. Documentation also tends to describe the intended surface rather than the actual one, so part of the work is establishing what is genuinely reachable.
Yes. APIs are tested directly against endpoints, so a user interface is not required. Credentials or tokens for each role are needed to assess authorization properly.
Broken Object Level Authorization is when an endpoint checks that you are logged in but not that the specific record you asked for is yours. It is common because the check has to be repeated correctly on every endpoint that touches an object, and one omission is enough.
Secure Your APIs
Send us the surface — endpoints, roles and what the data is worth — and we will scope testing around the boundaries that matter.