OWASP API Security Top 10:2023 for Penetration Testers

How to use the list

The topic 'How to use the list' is a central part of working on OWASP API Security Top 10 2023. It is recommended to break it down into three questions: what is the input, what decision needs to be made, and what evidence is sufficient to justify it. These questions prevent automatic tool usage without understanding the purpose.

In practice, document BOLA, Broken Authentication, Object Property Authorization, Unrestricted Resource Consumption, Sensitive Business Flows, compare to expected behavior, and define at least one pivot. The result should be testable by another analyst, including limitations and next steps.

Authorization risks

In OWASP API Security Top 10 2023, identity and authorization are two different questions: who is the client, and what is it allowed to do on the resource. Test Roles, Claims, Session, Object ownership, and changes throughout the lifecycle, rather than just assuming the user is 'logged in'.

A test matrix includes an anonymous user, a regular user, an object owner, another user, and an administrator. For each action, compare the Response and server-side impact. Changing an identifier or Header is only a testing means; the evidence is whether the server approved or rejected an action contrary to policy.

Authentication and Resource consumption

In OWASP API Security Top 10 2023, identity and authorization are two different questions: who is the client, and what is it allowed to do on the resource. Test Roles, Claims, Session, Object ownership, and changes throughout the lifecycle, rather than just assuming the user is 'logged in'.

A test matrix includes an anonymous user, a regular user, an object owner, another user, and an administrator. For each action, compare the Response and server-side impact. Changing an identifier or Header is only a testing means; the evidence is whether the server approved or rejected an action contrary to policy.

Business flows and Inventory

The topic 'Business flows and Inventory' is a central part of working on OWASP API Security Top 10 2023. It is recommended to break it down into three questions: what is the input, what decision needs to be made, and what evidence is sufficient to justify it. These questions prevent automatic tool usage without understanding the purpose.

In practice, document BOLA, Broken Authentication, Object Property Authorization, Unrestricted Resource Consumption, Sensitive Business Flows, compare to expected behavior, and define at least one pivot. The result should be testable by another analyst, including limitations and next steps.

Mapping to a Test plan

Professional testing for OWASP API Security Top 10 2023 begins with success and failure conditions. Define a positive Case, negative Case, boundary Case, and similar legitimate activity. This allows for identifying both False Negative and False Positive.

In an authorized environment, use minimal action that proves the claim without causing damage. Save Input, Output, time, and version, and after remediation, perform Retest in the same scenario and also check for Regression on nearby functions.

Unique testing focus areas

In this topic, it is recommended to build a focused evidence map in advance. The main testing focus areas are: BOLA, Broken Authentication, Object Property Authorization, Unrestricted Resource Consumption, Sensitive Business Flows, Unsafe Consumption. The list is not an automatic Checklist; each item is chosen because it can connect an entity, action, and time or explain legitimate behavior.

• BOLA: Define the expected value, what would be considered anomalous, and what additional source would confirm the finding.
• Broken Authentication: Define the expected value, what would be considered anomalous, and what additional source would confirm the finding.
• Object Property Authorization: Define the expected value, what would be considered anomalous, and what additional source would confirm the finding.
• Unrestricted Resource Consumption: Define the expected value, what would be considered anomalous, and what additional source would confirm the finding.
• Sensitive Business Flows: Define the expected value, what would be considered anomalous, and what additional source would confirm the finding.
• Unsafe Consumption: Define the expected value, what would be considered anomalous, and what additional source would confirm the finding.

When one of the focus areas is unavailable, document the gap and choose an alternative. For example, if a Process identifier is not stable, you can use time, Host, User, and Parent; if the Payload is encrypted, use Metadata, volume, frequency, and TLS/DNS context.

Recommended workflow

1. Define a Scope and one working question on OWASP API Security Top 10 2023.
2. Document the data sources and required evidence: BOLA, Broken Authentication, Object Property Authorization, Unrestricted Resource Consumption.
3. Create a short Baseline of normal behavior or expected outcome.
4. Perform the minimal test in a lab environment and save time, input, and output.
5. Build a Timeline or comparison table and separate facts from interpretation.
6. Pivot to an additional source to confirm or refute the initial explanation.
7. Conclude with a decision, limitations, recommended action, and Retest criterion.

Practical scenario

The chosen scenario is a Category-to-Test-to-Fix table. The purpose of the exercise is not to prove attack capability, but to practice safe collection, comparison, and documentation. Before starting, define simulated data, a time window, and an expected outcome.

At the end of the exercise, submit a product that another analyst or tester can review: a screenshot or Export of the evidence, a short Timeline, an initial assumption, corroborating evidence, limitations, and a recommendation. When there is insufficient evidence, the correct conclusion is that the scenario was not proven.

Practical Checklist

• ✓Check and document: Role and session.
• ✓Check and document: Endpoint and method.
• ✓Check and document: Request/Response.
• ✓Check and document: Object identifier.
• ✓Check and document: Server-side effect.
• ✓Check and document: Control expected and remediation.
• ✓Note Time zone, tool version, and collection time.
• ✓Save the raw data before filtering or modifying.
• ✓Write what the finding proves and what is still unknown.
• ✓Define owner and next action with a due date.

Common mistakes

• Only checking Status code.
• Relying on Client-side changes.
• Using a dangerous Payload.
• Not checking different Roles.
• Ignoring business logic.
• Reporting without clean Request/Response.

Summary and CTA

OWASP API Security Top 10:2023 for Penetration Testers is a topic that connects technical knowledge with work discipline. Start with a question, collect only relevant evidence, maintain context and time, and choose an action that can be justified and re-tested.

In HPI's Cybersecurity & AI program, these principles are practiced using systems, logs, and labs. The natural next step is to move on to the linked articles, perform the lab exercise, and save the output as part of a professional portfolio.

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