How to secure APIs using the OWASP API security top 10

APIs are the backbone of modern applications—but they also present a growing attack surface. With businesses relying heavily on APIs to power their platforms, services, and apps, security has become a top priority. The OWASP API Security Top 10 is the industry standard for identifying and mitigating the most critical API threats. Here’s a guide to securing your APIs against these common vulnerabilities.

1. Broken object level authorisation (BOLA)

BOLA occurs when APIs fail to properly verify a user’s access rights to specific resources. Attackers can manipulate object IDs to access data they shouldn’t.

How to protect:

• Enforce user-level access control checks on every request.
• Do not rely solely on object IDs passed in requests.
• Use centralised authorisation logic across endpoints.

2. Broken user authentication

Weak or improperly implemented authentication mechanisms allow attackers to impersonate users or access protected endpoints.

How to protect:

• Use industry standards like OAuth 2.0 and OpenID Connect.
• Implement rate limiting and account lockout policies.
• Always require strong passwords and multi-factor authentication (MFA).

3. Excessive data exposure

APIs often return more data than needed, exposing internal fields or sensitive information.

How to protect:

• Only return the minimum required data in responses.
• Use object whitelisting, not blacklisting.
• Avoid relying on client-side filtering for data protection.

4. Lack of resources and rate limiting

Without proper limits, APIs can be overwhelmed by excessive requests, leading to denial-of-service (DoS) attacks or infrastructure costs.

How to protect:

• Implement rate limiting, throttling, and quotas per user or IP.
• Set resource consumption limits (e.g. payload size, concurrent connections).
• Use caching and load balancing to absorb spikes in traffic.

5. Broken function level authorisation

APIs with role-based endpoints (e.g. admin vs user) sometimes fail to restrict access properly, allowing attackers to escalate privileges.

How to protect:

• Define roles and permissions clearly for each endpoint.
• Enforce checks on both the route and the business logic level.
• Log and audit access to sensitive operations.

6. Mass assignment

This vulnerability occurs when APIs automatically bind request data to internal objects, allowing attackers to update unintended fields.

How to protect:

• Use whitelists to control which fields can be updated.
• Sanitise and validate all input data.
• Avoid using frameworks’ default deserialisation without control.

7. Security misconfiguration

Insecure headers, verbose error messages, and misconfigured permissions expose APIs to attackers.

How to protect:

• Disable unnecessary features and services.
• Use security headers like Content Security Policy (CSP) and HTTP Strict Transport Security (HSTS).
• Hide stack traces and sensitive debug information in production.

8. Injection

APIs vulnerable to injection flaws—like SQL, NoSQL, or command injection—can be manipulated by attackers to access or alter data.

How to protect:

• Use parameterised queries and ORM libraries.
• Sanitise all user inputs.
• Employ input validation and schema enforcement.

9. Improper assets management

Forgotten or outdated API versions, exposed staging environments, or undocumented endpoints increase the risk of attacks.

How to protect:

• Maintain an inventory of all APIs and versions.
• Decommission or block outdated endpoints.
• Label internal, beta, or staging APIs clearly and restrict access.

10. Insufficient logging and monitoring

Without proper logging and alerting, suspicious activity can go unnoticed, increasing breach detection time.

How to protect:

• Log all access attempts, errors, and unusual activity.
• Use automated alerts for security anomalies.
• Retain logs securely and ensure they are tamper-resistant.

Final thoughts

Securing your APIs is not optional—it’s essential. The OWASP API Security Top 10 provides a clear framework for identifying the most common and damaging vulnerabilities. By addressing each one systematically, you can reduce your attack surface, protect user data, and build trust with your customers.

Whether you're running a startup or an enterprise-scale platform, integrating security best practices from day one is far easier than retrofitting it later. For startups and dev teams using platforms like Gateway APIs, choosing trusted, well-secured APIs can further reduce risk and improve your security posture.