What Is API Security? OWASP API Security Top 10 and BOLA Risks

What Is API Security?

An Application Programming Interface (API) is the interface that allows different software to communicate with each other in a secure and controlled way. Today, most of the data exchange between web applications, mobile applications, desktop software, cloud services and third-party integrations takes place through APIs.

API security covers the evaluation of these services' controls for authentication, authorization, data validation, rate limiting, error handling and data sharing. APIs that are not designed securely can allow attackers to reach the data and business logic behind the application directly.

Why Are APIs a Primary Target for Attackers?

• APIs provide direct access to business logic.
• The same API can be used by both the web and mobile applications.
• Functions not visible in the user interface may be accessible via the API.
• Misconfigured APIs can return large amounts of data in a single request.
• In micro-service architectures, trust relationships between services can be mismanaged.

The Difference Between Web Security and API Security

Web Application Security	API Security
Interfaces accessed through a browser are evaluated	Service endpoints are evaluated directly
HTML, JavaScript and client behaviour are examined	JSON, XML, GraphQL and service responses are analysed
User-experience focused	Data-flow and business-logic focused

OWASP API Security Top 10 — The Most Common Risks

1. Broken Object Level Authorization (BOLA)

A user making a GET /api/orders/45872 request should only be able to see their own order. If the attacker changes the request to GET /api/orders/45873 and can access another customer's information, there is a serious authorization vulnerability. BOLA can lead to major data breaches in banking, healthcare, e-commerce and public-sector applications.

2. Broken Authentication

Accepting invalid tokens, allowing the use of expired sessions or JWT validation gaps can enable attackers to act as legitimate users.

3. Excessive Data Exposure

If the API returns more data than the client needs (national ID number, e-mail, phone, internal system notes, etc.), even if the client does not display it, the attacker can obtain that information by inspecting the API response.

4. Unrestricted Resource Consumption

The absence of rate limiting can allow attackers to send thousands of requests in a very short time, leading to service disruptions and brute-force attacks.

5. Security Misconfiguration

Leaving debug mode on, returning detailed error messages, enabling unnecessary HTTP methods, incorrect CORS settings and default accounts can broaden the attack surface.

A Real-World Scenario

During a security assessment of a customer portal running through a mobile application, it was found that on the API endpoint returning user profile information, simply changing the user identifier gave access to the full name, contact details, address records and order history of different customers. Even though no security problem was visible in the web interface, these sensitive data could be reached when the API calls were examined directly.

SecureSys API Penetration Testing Approach

Our tests cover the examination of REST API and GraphQL services, verification of JWT and OAuth flows, testing of BOLA and IDOR scenarios, parameter manipulation, mass-assignment checks, verification of rate-limiting mechanisms, and examination of CORS configurations.

Key Recommendations for API Security

• Object-level authorization must be checked at every endpoint.
• Returned data must be limited to only the fields the client needs.
• JWTs and access tokens must be validated securely.
• Rate limiting and quota mechanisms must be applied.
• All API calls must be centrally monitored and logged.

To have your APIs tested against BOLA, Broken Authentication and other OWASP API Security Top 10 risks, get in touch. You can also review our Web Application Penetration Testing Service page.