API Penetration Testing

Built fast, tested never. Let's change that.

Secure your REST, GraphQL, and SOAP APIs against data exposure and unauthorised access. OWASP API Top 10 aligned testing by certified consultants.
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Accreditations and memberships

CREST Pathway member Cyber Essentials certified UK Cyber Security Council member
API penetration testing services for REST, GraphQL, and SOAP APIs

Who Needs This

Who needs API penetration testing?

APIs are the backbone of modern applications, but they are also one of the most common sources of data breaches. Any organisation that exposes or consumes APIs should have them tested regularly.

API-first companies and microservices

API-first architectures surface every function directly through exposed endpoints. Missing authentication, broken object-level authorisation, and mass assignment are common findings.

Mobile app backends

Mobile applications communicate with backend APIs that are often less well-tested than their web counterparts. Rate limiting, authentication weaknesses, and data exposure are common.

Public API services

APIs consumed by third-party developers or partners require rigorous testing. Security issues in public APIs affect all consumers and can be discovered and exploited by anyone with API access.

Internal APIs and integrations

Internal APIs between services often lack the same security controls applied to external-facing endpoints. Broken function-level authorisation and insufficient validation are frequent findings.

Our Pentest Methodology

OWASP API Top 10 aligned testing

Our API testing methodology is aligned with the OWASP API Security Top 10, combining automated discovery with manual exploitation to find vulnerabilities that scanners miss.
01

Broken Object Level Authorisation

Testing whether API endpoints enforce object-level access controls, allowing users to access or manipulate resources belonging to other users by modifying object references.
02

Broken Authentication

Assessment of token generation and handling, session management, credential policies, and whether authentication mechanisms can be bypassed or abused.
03

Broken Function Level Authorisation

Identifying whether administrative or privileged API functions are accessible to lower-privileged users by manipulating HTTP methods, endpoints, or request parameters.
04

Excessive Data Exposure

Reviewing whether API responses return more data than is required by the client, exposing sensitive fields that could be harvested by an attacker.
05

Rate Limiting & Resource Consumption

Testing whether API endpoints enforce appropriate rate limits and whether resource consumption can be exploited to degrade service or enumerate data at scale.
06

Security Misconfiguration

Assessment of CORS policy, security headers, verbose error messages, exposed debugging endpoints, and unnecessary HTTP methods.

Pricing

From £1,800

for API penetration testing

Not sure where your application fits? A 30-minute scoping call is free and gets you a fixed written quote.

Book scoping call Request a quote

No obligation · Strictly confidential · Quote within one business day

Pricing Examples

Simple REST API (5-20 endpoints)£1,800 - £2,200
Standard API (20-50 endpoints, multiple roles)£2,200 - £3,800
Complex API with multiple auth methods£3,800 - £5,700
GraphQL or microservices architecture£5,700+
Indicative ranges only. Your exact price is confirmed after a short scoping conversation - see full service pricing.

What's Included

  • Fixed-price proposal within one business day
  • Manual, consultant-led testing. Not automated scans
  • Report within 2 business days of testing completion
  • Free focused retesting included to verify remediation
  • No obligation quote, all enquiries are fully confidential

Key Deliverables

What's included in the assessment?

Every API penetration test includes deliverables that provide your team with the information they need to understand and fix identified vulnerabilities, and stakeholders with the information they need to understand business risk.

Executive Report

A non-technical pentest report containing detailed findings, with risk ratings and recommendations suitable for board and senior management stakeholders.

Technical Report

Detailed findings with reproduction steps, severity scoring, remediation guidance, and mappings to CVE, CVSS, and OWASP API Top 10 where applicable.

Debrief Session

An offer of a debrief call to walk through findings, discuss remediation priorities, and answer questions from both technical and executive stakeholders.

Free Retesting

Complimentary focused retesting of any remediated vulnerabilities to verify that identified issues have been properly resolved.

Attack Surface Center Access

Complimentary access to our Attack Surface Center ASM platform for collaborative tracking and remediation management throughout and beyond the engagement.

Consultant-led Testing

All testing is consultant-led by in-house staff. Your consultant works with you from scoping through to debrief - nothing is outsourced or subcontracted.

Common Questions

API penetration testing - frequently asked questions

Most API tests take 3-7 days depending on the number of endpoints, complexity of the functionality, and API architecture. Reports are delivered within 2 business days of testing completion.

Yes, we can reverse-engineer and test undocumented APIs through traffic analysis, endpoint discovery, and behaviour observation. Testing is more efficient when OpenAPI/Swagger documentation or Postman collections are provided.

If you have a web application or mobile application that consumes the API, we'd highly recommend focusing testing through one of those services if you do not have API documentation available.

Yes, GraphQL APIs have a distinct attack surface including introspection abuse, deeply nested query attacks, and broken authorisation between operations. We test these specifically as part of GraphQL engagements.

Most testing activities are designed to be non-disruptive. However, certain tests such as rate limit abuse or resource exhaustion may cause temporary performance degradation. We can coordinate testing to minimise impact, and we always recommend testing against staging environments where possible.

Yes, API testing is included when APIs are part of the application's functionality. For dedicated API-only products or microservices architectures, a standalone API penetration test provides more thorough coverage.

Yes, internal API testing can be performed from within your network or via a provided VPN connection. Internal APIs are often less rigorously tested than public-facing endpoints and frequently contain significant vulnerabilities.

We work with you to understand your authentication mechanisms and obtain necessary credentials or tokens for testing. We can test a variety of authentication methods including API keys, OAuth, JWT, and custom schemes. We also test for weaknesses in token handling and session management.

Ready to secure your APIs?

Get a fixed-price quote within 24 hours. Our team will review your API's scope and provide a tailored testing proposal that fits your timeline and budget.

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