What we assess
Object and function authorization
Cross-account access, tenant boundaries and privileged endpoint permissions.
Tokens and identity
Token lifecycle, audience and scope enforcement, expiry and authentication boundaries.
Schemas and responses
Input validation, unexpected properties, unsafe URL handling and excess data exposure.
Workflow and resource controls
Business sequence enforcement, pagination and agreed, bounded checks of abuse controls.
Who it is for
Teams building customer-facing APIs, mobile backends, partner integrations and multi-tenant services.
Before we start
Share an endpoint inventory or API specification, authentication approach, roles, integration boundaries and test-environment details. Agree representative objects and test identities without sharing production secrets through this site.
Methodology
From scope to verified fixes.
Build an endpoint and role matrix. Compare authorized and unauthorized actions using synthetic records, then validate sensitive flows across connected endpoints. OWASP API guidance informs coverage, while resource-intensive checks require explicit limits and approval.
- Agree authorization, coverage, test limits and evidence handling.
- Discover and manually validate candidate weaknesses.
- Report confirmed findings, unverified observations and coverage limitations distinctly.
- Discuss remediation and retest the specified fixes within the agreed window.
Typical issues we look for
Examples of possible issues, not findings from R53SEC client engagements. Actual results depend on the system and scope.
- An object identifier exposes another customer’s data despite a valid login.
- An ordinary user can invoke an administrative function.
- An API accepts a protected property from a client and changes a value the user should not control.
What you receive
An endpoint/role coverage matrix, request and response evidence with sensitive values removed, impact explanations and remediation at the relevant authorization or validation boundary.
The report includes an executive summary, finding identifiers, severity rationale, impact, evidence, remediation and coverage limitations. CVSS is included where appropriate with its version, vector and assumptions. Retest scope, timing and commercial terms are agreed before work begins.
Questions about API Security Testing
Do you need an OpenAPI specification?
It helps define coverage, but an endpoint inventory and documented workflows can also support scoping. Undocumented endpoints discovered within scope are discussed with your team.
Is TLS enough to make an API secure?
TLS protects transport. It does not determine whether an authenticated caller may access an object or perform a business action.
Will testing overload the API?
Rate limits and exclusions are agreed in advance. Load testing and denial-of-service testing are separate activities and are not assumed to be authorized.
Related services
Practical reading
Guides
API Security Best Practices
A practical review of API identity, object authorization, schemas and evidence.
Read articleGuides
OWASP Top 10 for Modern Applications
Use OWASP guidance to structure web testing around authentication, authorization and business workflows.
Read article