API Security Testing
Your APIs are the backbone of your product — and one of the most attacked surfaces on the internet. Broken authorisation, exposed endpoints, and missing rate limits can hand an attacker your entire customer dataset.
What is API Security Testing?
Comprehensive security testing of your REST, SOAP, and GraphQL APIs to uncover authentication weaknesses, authorisation flaws, injection vulnerabilities, and business logic issues.
APIs are increasingly targeted because they sit at the boundary between your frontend, your backend, and third-party integrations — and are frequently deployed without the same security scrutiny applied to web applications.
At a Glance
- Frameworks
- OWASP API Security Top 10, OWASP Testing Guide
- Typical Timeline
- 3–7 days depending on API complexity and number of endpoints
- Report
- Executive summary + full technical findings
- Retest
- Complimentary, included in every engagement
- NDA
- Signed before any technical discussion
Outcomes that move your security forward
What You Receive
Executive Summary Report
Overview of API security posture and key risk findings
Full Technical Report
All findings mapped to OWASP API Security Top 10 with endpoint references, proof-of-concept, and CVSS scores
API Endpoint Inventory
Complete documented list of all discovered and tested endpoints
Developer Remediation Guide
Endpoint-specific fix guidance written for backend developers
Retest Report
Confirms critical and high findings resolved after remediation
What We Test
How We Run This Engagement
Every engagement follows a defined, transparent process — no surprises, no hidden scope changes, and no invoice for work you did not agree to.
Scoping
Document all API endpoints, authentication flows, and roles.
Mapping & Reconnaissance
Build a full inventory of endpoints, parameters, and data flows.
Authentication & Authorisation Testing
Attempt to bypass authentication and access controls.
Injection & Business Logic Testing
Test all parameters for injection and logic flaws.
Reporting
Findings mapped to OWASP API Security Top 10 with remediation guidance.
Retest
Verify that identified vulnerabilities have been fixed.
Why Work With Vigilant Defenders
Manual Testing. Not Scanner Output.
Automated tools find known signatures. Our certified consultants find the chained attack paths, logic flaws, and context-specific vulnerabilities that no scanner will surface. Every finding we report is manually verified — zero false positives.
Reports Built for Action, Not Filing.
Every finding includes a proof-of-concept, a CVSS risk score, the affected system or endpoint, and step-by-step remediation guidance written for the team that has to fix it. Your developers and your board both get a report they can use.
Confidentiality From Day One.
We sign a formal NDA before any technical discussion begins. Your vulnerabilities, your architecture, and your engagement findings are treated with the same confidentiality as attorney-client communications. We have never disclosed client information.
We Stay Until It's Fixed.
Every engagement includes a complimentary retest once your team has addressed the findings. We verify that the vulnerabilities are genuinely closed — not surface-patched — and issue a formal retest certificate you can share with clients and auditors.
We Test APIs the Way Attackers Actually Probe Them.
We don’t just run an OWASP API checklist. We map every endpoint, test access across all authentication states, and attempt to chain findings together. If one user can reach another user’s data through a single API call, we’ll find it.
Frequently asked questions
Everything you need to know about this engagement.
We test REST, SOAP, GraphQL, and gRPC APIs. We work with both internal APIs and publicly exposed APIs.
Related services
Web App Pen Testing
OWASP-aligned manual testing covering authentication, access control, and injection.
Learn moreFind Out What's Exposed in Your API Layer
Get a free scoping consultation — no commitment required. We’ll scope the right API security testing engagement for your environment and send a fixed-fee proposal within 24 hours.