API Penetration Testing

What is an API penetration test?

An API is the communication layer between systems, such as a mobile app talking to a backend, or a web application fetching data. Modern applications depend heavily on APIs, and they have become an attractive target because they often expose the same data and functionality as the user-facing interface, but with fewer protective controls.

The test evaluates your APIs from an attacker’s perspective, looking for weaknesses that could lead to unauthorised data access, restricted actions being performed, or application security controls being bypassed.

What we test

Testing follows the OWASP API Security Top 10 and covers:

• Broken object-level authorisation: verifying users can only access objects they are permitted to view. This is the most common API vulnerability.
• Broken authentication: checking whether authentication can be bypassed, tokens are validated properly, sessions are handled correctly, and whether any endpoints lack authentication entirely.
• Broken object property-level authorisation: ensuring APIs do not return excessive data or accept changes to restricted fields.
• Unrestricted resource consumption: confirming rate limiting exists and that denial-of-service or cost-escalation attacks are not feasible.
• Broken function-level authorisation: validating that privileged endpoints stay restricted to authorised users.
• Injection: testing for SQL injection, command injection and similar flaws through API parameters.
• Security misconfiguration: default settings, unnecessary HTTP methods, overly permissive CORS policies, missing headers, and revealing error messages.
• Improper inventory management: checking whether outdated API versions and deprecated endpoints with weaker controls remain accessible.

Who needs an API penetration test?

You should consider testing if you:

• Expose APIs to customers, partners, or internal front-end applications.
• Integrate with payment providers, identity platforms, CRMs, or other third-party services.
• Operate APIs within PCI DSS or ISO 27001 scope.
• Plan to launch a new API or deploy a major version update.

What the process looks like

The process begins with a scoping discussion covering the available APIs, their functions, and the state of their documentation. Testing uses a grey-box model with credentials for different user roles, which enables thorough authorisation testing and uncovers logic-level issues that a black-box approach would miss.

Duration varies with the number of endpoints and the complexity of the authorisation model. The report includes severity ratings, clear explanations of each vulnerability, what an attacker could do with it, and specific remediation guidance for your development team.

Retesting

After your developers address the findings, a retest confirms the fixes work, which is particularly valuable before a product launch, a security audit, or a compliance review.