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Offensive Security

API Security Testing

Testing for REST, GraphQL and SOAP APIs aligned to the OWASP API Security Top 10 — authorization, authentication, rate limiting and the data-exposure issues APIs are prone to.

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Overview

The attack surface behind every modern app.

APIs power your apps, partners and integrations — and carry their own distinct risks. Object-level authorization gaps, broken authentication and excessive data exposure are common and frequently missed by web-focused testing.

We assess your APIs against the OWASP API Security Top 10, exercising each endpoint, parameter and authorization boundary to find where data or functionality is exposed beyond what was intended.

What we test

Focus areas of the assessment.

The core areas we examine in a api security testing engagement.

Broken object-level authorization

BOLA / IDOR issues exposing other users’ data through the API.

Broken authentication

Token, key and session weaknesses in API access control.

Excessive data exposure

Endpoints returning more data than the client should ever receive.

Rate limiting & resource abuse

Missing throttling enabling brute-force, scraping and denial-of-service.

Injection & mass assignment

Input-driven flaws and over-permissive object binding.

Inventory & shadow APIs

Undocumented, deprecated or forgotten endpoints still exposed.

Who needs this

Is this the right fit?

The organisations that most often turn to this engagement.

API-first / SaaS platformsCore product exposed through APIs.

Fintech & open-banking providersAccount and payment APIs under regulation.

Mobile app backendsAPIs powering mobile clients.

B2B integration platformsPartner-facing endpoints.

Microservices architecturesMany internal and external service boundaries.

Anyone exposing public APIsData-exposure and authorization risk.

Regulatory drivers

Why this is required

APIs now carry the majority of sensitive and payment traffic and are explicitly in scope of payment, banking and privacy obligations, so testing them to the OWASP API Top 10 has become a baseline expectation.

PCI DSS v4.0

Applies wherever APIs transmit, or give access to, cardholder data — requiring secure development and regular vulnerability testing.

RBI / NPCI ecosystem

Payment and account-aggregator APIs carry specific security and testing expectations across the regulated payments ecosystem.

DPDPA & GDPR

Require security of processing for APIs that expose or handle personal data, including access-control and data-exposure testing.

OWASP API Security Top 10

The de-facto benchmark that assessors and enterprise partners expect API testing to be measured against.

How we work

A disciplined testing methodology.

A repeatable, standards-based process that balances depth with operational safety.

Scoping & specification review

Reviewing the API spec (OpenAPI/Postman), auth model and data flows.

Endpoint & auth enumeration

Enumerating endpoints, methods, tokens and authentication mechanisms.

Access-control testing

Testing for BOLA, BFLA and broken object- and function-level authorization.

Input, injection & rate-limit testing

Probing inputs, injection, mass assignment and rate-limiting controls.

Exploitation & data-exposure validation

Confirming excessive data exposure and exploitable flaws with evidence.

Reporting & retest

Risk-rated findings mapped to the OWASP API Top 10, with a retest.

What you receive

Deliverables built for every audience.

Executive summaryOverview of API risk posture and key themes.
OWASP API Top 10 findingsEach issue mapped to the OWASP API Top 10 with evidence.
Proof-of-concept evidenceEndpoint-level requests and steps to reproduce.
Remediation guidancePractical fixes for authorization, input and exposure issues.
Retest report & attestationVerification of fixes with an attestation letter.

Standards & frameworks

This assessment is aligned to recognised industry methodologies.

OWASP API Security Top 10OWASP ASVSPTESNIST SP 800-115

Checklist

Are you ready? A quick checklist

What to have in place before we begin.

API base URLs and environments listed

Documentation (OpenAPI/Postman) shared

Test credentials and keys per role

Rate-limit considerations agreed

Sandbox vs production decided

Sample request/response payloads

Partner / third-party boundaries flagged

Remediation owner identified

FAQ

Common questions

Do you need API documentation?

Documentation such as an OpenAPI/Swagger spec or Postman collection speeds testing and improves coverage, but we can also work from traffic capture and discovery where docs are incomplete.

Can you test GraphQL specifically?

Yes. GraphQL has its own concerns — introspection exposure, nested-query abuse and authorization at the resolver level — which we test in addition to standard API risks.

How is this different from web app testing?

APIs lack a UI and enforce authorization per-object and per-endpoint, so they need dedicated testing focused on authorization, data exposure and abuse rather than browser-driven flows.

What if we have hundreds of endpoints?

We risk-prioritise and sample representative endpoints while ensuring every critical and sensitive operation is fully covered. Rather than testing every endpoint identically, we focus depth where the data and impact are greatest — authentication, payments, personal data and admin functions — and confirm the rest behave consistently.