Beyond the UI. Into the API.

CREST-aligned API penetration testing with full OWASP API Security Top 10 coverage across REST, GraphQL, SOAP and gRPC.

Scope an API test See a sample report

OWASP API

Top 10 coverage

REST/GraphQL

Multi-protocol testing

CREST

Certified testers

5–10 days

Typical engagement

Who this is for

Built for teams whose API carries the business

API-first products

Companies whose API IS the product — developer tools, B2B SaaS, fintech infrastructure.

Microservice architectures

Engineering teams with REST/GraphQL/gRPC services that need authorisation and rate-limit validation.

Payment / sensitive data APIs

APIs that handle cardholder data, PHI, PII, or financial transactions where API breaks have regulatory weight.

What is API penetration testing?

The targeted, predominantly manual assessment of API endpoints for exploitable security weaknesses.

Modern APIs use a range of protocols (REST, GraphQL, SOAP, gRPC) and authentication schemes (OAuth 2.0, JWT, API keys, mTLS), each with characteristic weakness patterns testers must understand to assess effectively.

The threat landscape

OWASP API Security Top 10

Broken Object-Level Authorisation

BOLA — the #1 API risk.

Broken Authentication

Weaknesses in how identity is verified and sessions are managed.

Broken Object Property-Level Authorisation

Mass assignment — unintended properties written or exposed.

Unrestricted Resource Consumption

Rate limiting and denial-of-service exposure.

Broken Function-Level Authorisation

Endpoints reachable by roles that shouldn't be able to call them.

Server-Side Request Forgery

APIs tricked into making unintended internal or external requests.

Security Misconfiguration

Insecure defaults, verbose errors, and missing hardening.

Lack of Protection from Automated Threats

Insufficient defence against scripted abuse and scraping.

Improper Inventory Management

Undocumented, deprecated or shadow API versions left exposed.

Unsafe Consumption of APIs

Trusting third-party API data and responses without validation.

What API testing delivers

Depth where APIs actually break

OWASP Top 10 coverage

OWASP API Security Top 10 coverage across all endpoints.

Authorisation matrix testing

Systematic testing across roles and objects, not spot checks.

Mass assignment & data exposure

Identification of unintended property writes and excessive data exposure.

Rate limiting & abuse testing

Rate limiting and abuse vector testing against scripted attacks.

Authentication & token handling

Validation of authentication flows and token handling end to end.

Business logic testing

Manual testing of API workflows for logic flaws automated tools miss.

API testing has become as important as traditional web application testing — and arguably more important for organisations whose APIs back mobile apps, B2B partners, or microservice architectures.

Why API security testing matters

APIs are now the dominant attack surface

Mobile apps, single-page web apps, B2B integrations, and microservice architectures all expose far more API surface than traditional web pages — and developers consistently apply weaker authorisation logic to API endpoints than to UI-fronted equivalents, on the assumption that “no one will call the API directly.” They will.

Major breaches in 2024 and 2025 have repeatedly traced back to API-level vulnerabilities: BOLA in mobile app backends exposing customer records, mass assignment in admin APIs enabling privilege escalation, weak rate limiting enabling credential stuffing at scale.

Customer record exposure via BOLA in mobile/SPA backends
Privilege escalation via mass assignment in admin APIs
Credential stuffing at scale due to weak rate limiting
Sensitive data exposure via verbose API responses
Account takeover via authentication weaknesses
Compliance failures across PCI DSS and SOC 2

Who needs API testing?

Any organisation operating APIs

Internal microservices, mobile app backends, public APIs, B2B integrations — if your API handles sensitive data, dedicated API testing is essential. Generic web application testing rarely covers API security depth.

SaaS with mobile & SPA frontendsMobile-first companiesOpen banking & PSD2 APIsPayment platformsAI/ML platforms with API surfacesMicroservice architecturesB2B platforms with partner APIsHealthTech with FHIR APIs

How we work

Our API testing methodology

CREST-aligned methodology combining the OWASP API Security Top 10 with hands-on, protocol-specific testing across REST, GraphQL, SOAP and gRPC. Typical engagement: 5–10 days for mid-complexity APIs (under 50 endpoints), 10–15 days for larger APIs (50–150 endpoints), longer for major platforms.

01
Scoping & API documentation review
We agree the in-scope endpoints (typically from OpenAPI/Swagger, GraphQL schema or Postman collections), user roles, authentication schemes and test credentials.
02
Endpoint enumeration & mapping
Complete mapping of every endpoint, method, parameter and response shape, building the full attack surface before testing begins.
03
Authentication & token testing
JWT validation, OAuth flow integrity, token refresh logic, session fixation and brute-force resistance.
04
Authorisation matrix testing
Systematic testing of object-level and function-level authorisation across every user role pair — the highest-value work in any API engagement.
05
Mass assignment & data exposure
Unintended property writes, verbose responses leaking sensitive data, and improper input filtering.
06
Rate limiting & abuse testing
Rate limiting, account lockout and abuse vectors that enable credential stuffing or data scraping at scale.
07
Business logic & workflow testing
Manual exploration of workflows for parameter tampering, race conditions and logic flaws automated tools cannot find.
08
Reporting & developer walk-through
Findings with curl/Postman reproduction steps, code-level remediation guidance, and a live walk-through with your engineers.

What you receive

Every API engagement includes

Scoping document

Full endpoint inventory agreed before testing begins.

Executive summary

Written for board and management consumption.

Technical findings

Detailed, with curl/Postman reproduction steps.

Exploitability prioritisation

CVSS scoring plus real-world exploitability context.

Remediation guidance

Code-level, with worked examples for your engineers.

Authorisation matrix report

Full test coverage across every role and object.

OWASP compliance mapping

Findings mapped to the OWASP API Security Top 10.

Remediation retest

Critical and high findings re-verified at no extra cost.

Industries we serve

Delivered across regulated sectors

Financial ServicesHealthcareSaaS & TechnologyE-commerce & RetailDefence & GovernmentCloud & Managed ServicesEducationProfessional Services

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