API Penetration Testing
APIs are where the real data lives — and where authorization bugs hide. We test your REST and GraphQL endpoints against the OWASP API Top 10 and the object-level access issues that dominate modern breaches.
What is API Penetration Testing?
APIs expose your data directly, and authorization is where they fail. We enumerate every endpoint and object, then test whether one user can read or change another's data — the broken object-level authorization that tops the OWASP API list and drives most modern breaches.
Modern products are mostly API behind a thin client, and the client's restrictions mean nothing to an attacker calling the API directly. The mobile app hides a field; the API still returns it. The UI never shows an admin button; the endpoint still honours the request. We test the API on its own terms — every method, every object, every role — because that's exactly how it will be attacked.
APIs also fail in ways UIs rarely do because they're built for machines and change fast. Versioned endpoints linger after they're deprecated, internal APIs get exposed 'temporarily', and documentation drifts from reality. We enumerate what actually exists — not just what's documented — and test every version and method, because attackers target the forgotten v1 endpoint that never got the authorization fix the v2 did.
API Penetration Testing is a manual, exploit-driven assessment: real people attacking your target the way an adversary would, then proving each finding with a working proof of concept. It is not an automated scan with a logo on it — the point is to find and demonstrate the issues that actually put you at risk, and hand your team a clear plan to fix them.
Why it matters
Applications are the most-attacked surface on the internet, and a single exploitable flaw can expose your entire customer base. Scanners catch the obvious; the damaging bugs live in logic and authorization, where only manual testing reaches them.
A api penetration testing engagement replaces guesswork with evidence. Instead of hoping your controls hold, you get a ranked, reproducible picture of where they don’t — before someone hostile finds the same gaps.
Industries & use cases
API testing is critical for fintech and open-banking platforms, mobile-app backends, B2B integrations and any headless or microservice architecture. Wherever partners, mobile clients or third parties call your endpoints directly, the API — not the UI — is the real attack surface, and object-level authorization is where it breaks.
What we test
Manual, exploit-driven coverage focused on real impact — not scanner noise.
- Broken object-level authorization (BOLA/IDOR)
- Broken function-level authorization
- Mass assignment and excessive data exposure
- Authentication and token handling
- Rate-limiting and resource abuse
- Injection and SSRF via API parameters
Signs you should run a api penetration testing
If any of these apply, testing is overdue.
- You expose public, partner or mobile APIs
- You've adopted microservices or a GraphQL layer
- You added endpoints faster than you documented them
- Partners or third parties integrate directly with you
- You need OWASP API Top 10 coverage for compliance
Common vulnerabilities we find
The issues that show up again and again in api penetration testing — and the ones that actually get exploited.
Broken object-level authorization (BOLA)
Changing an ID in the request returns another tenant's or user's object because ownership is never checked.
Mass assignment
Extra fields in a request set attributes the user should never control, such as role or account balance.
Excessive data exposure
The API returns full objects and the client hides fields, leaking data any caller can read directly.
Rate-limiting and resource abuse
Missing limits allow credential stuffing, enumeration and denial of service against expensive endpoints.
Injection via API parameters
Unsanitised values in JSON, headers or query strings reach databases, commands or downstream services.
Improper inventory / shadow APIs
Undocumented, deprecated or debug endpoints still live and unprotected.
Server-side request forgery
An API parameter makes the server fetch attacker-chosen URLs, reaching internal services.
Security misconfiguration
Verbose errors, permissive CORS and missing security headers on API responses.
Example attack chain
Real impact rarely comes from one bug — it comes from chaining several. A representative example:
Why choose webhook.press
Attacker mindset
We’re offensive security people who also build the free tools bug-bounty hunters use daily. We test the way real adversaries do — and prove it.
No scanner theatre
You get findings a human exploited and verified, ranked by real business risk — not an unfiltered tool dump padded to look thorough.
Fixed price, free retest
A clear quote after scoping, a report your team and auditors can use, and a free retest to confirm the fixes hold.
Our methodology
A structured, transparent process aligned to OWASP and PTES — with a named point of contact throughout.
Scoping & rules of engagement
We agree the exact targets, depth, timing and constraints for your api penetration testing, and set clear rules of engagement so testing is safe and predictable.
Reconnaissance & mapping
We enumerate the full attack surface — endpoints, roles, technologies and trust boundaries — and threat-model where an attacker would focus.
Manual testing & exploitation
We attack by hand, verifying and chaining weaknesses into real impact. Automated tooling supports coverage; humans find the logic and authorization bugs it can’t.
Analysis & risk rating
Each finding is validated, rated by real business risk rather than raw scanner severity, and de-duplicated so you get signal, not noise.
Reporting
You receive an executive summary for leadership and a technical section with reproducible PoCs, evidence and concrete, stack-specific remediation.
Free retest
After you remediate, we re-test the closed findings to confirm they are actually fixed — at no extra cost.
What you get
Reproducible PoCs
Every finding ships with a working proof and step-by-step reproduction your engineers can replay and verify.
Risk-ranked findings
Prioritised by real business impact, so you fix what matters first instead of drowning in low-severity noise.
Actionable remediation
Concrete, stack-specific fixes and guidance — not generic “apply best practice” filler.
Free retest
We re-check the closed findings after remediation and confirm they’re resolved.
The report is written for two audiences at once: an executive summary that a non-technical stakeholder can act on, and a detailed technical section — findings, evidence, CVSS and reproduction — that your developers and auditors can use directly.
Manual testing, not just a scan
Automated scanners are fast and useful for coverage, but they only find patterns they already know, and they flood you with false positives. They cannot understand your business logic, chain several small issues into a breach, or tell you which alert actually matters. Our api penetration testing is led by experienced testers who exploit findings by hand and rank them by the damage they’d really do — the difference between a 300-page tool dump and a short list of things worth fixing.
Standards & compliance
Our api penetration testing reports are written to support the frameworks your auditors and customers care about — including SOC 2, ISO 27001, PCI DSS, HIPAA, GDPR, and the EU’s NIS2 and DORA. Each engagement produces clear, independent evidence of testing with scope, methodology and findings documented the way assessors expect, so the same test both hardens your systems and helps satisfy your obligations.
Frameworks we follow
Recognised methodologies, adapted to your target — never a rigid checklist.
- OWASP — Web Security Testing Guide, ASVS and the API Security Top 10
- PTES — the Penetration Testing Execution Standard
- NIST SP 800-115 — technical guide to security testing
- OSSTMM — Open Source Security Testing Methodology Manual
- MITRE ATT&CK — to frame real-world adversary techniques
FAQ
Do you test GraphQL specifically?
Yes — introspection, nested-query DoS, field-level authorization and batching abuse are all in scope.
Do you need our API docs?
Docs (OpenAPI/Postman) speed things up and improve coverage, but we can also test undocumented endpoints.
Do you test REST and GraphQL?
Yes — both, including GraphQL-specific issues like introspection, nested-query DoS and field-level authorization.
How do you handle authentication for testing?
We use test accounts across roles and tenants so we can prove object- and function-level authorization gaps, the highest-impact API bugs.
Do you test all API versions?
Yes — including deprecated and undocumented versions, which frequently lack fixes present in the current one.
Can you work from an OpenAPI/Postman collection?
Yes — it speeds coverage; we also probe for endpoints beyond what's documented.
How long does a api penetration testing take?
Most focused engagements run one to two weeks depending on scope; we agree the exact timeline during scoping.
Is a retest included?
Yes — after you remediate, we re-check the closed findings to confirm they’re fixed, at no extra cost.
How do you price it?
Per engagement, based on scope and depth — you get a fixed quote after a short scoping call. No cookie-cutter packages.
Why teams trust our api penetration testing
Aligned to recognised standards
Testing follows OWASP, PTES, NIST SP 800-115 and MITRE ATT&CK, and reports support SOC 2, ISO 27001, PCI DSS, HIPAA, GDPR, NIS2 and DORA.
Every engagement includes
Reproducible PoCs, risk-ranked findings, concrete remediation, a named point of contact, a free retest, and a summary letter of attestation.
Confidential by default
Work is covered by an NDA, scoped with clear rules of engagement, and data is handled with care throughout — including residency requirements.
Sample report available on request — see our reporting format and depth before you commit. Ask for a sample →
Get a quote for API Penetration Testing
Tell us about the target — we’ll come back with scope and a fixed price. Manual, exploit-driven testing with reproducible proof and a free retest.