API Security Testing Best Practices- How to Test API Security
API security involves the measures taken to protect APIs from unauthorized access, misuse, and attacks. Because APIs are commonly used and enable access to sensitive software functions and data, they are becoming an increasingly desired target for attackers.
API security is a critical component of modern web application security. API security is essential for protecting sensitive data like financial information or personal data, and preventing attacks that could compromise the integrity of the API and the systems it connects to.
Why is API security testing important?
APIs enable businesses to integrate different systems and technologies by allowing various applications to communicate quickly, leading to more efficient and effective operations.
APIs, however, can also create potential security risks if they are not correctly managed and secured. Attackers have been known to exploit API vulnerabilities to gain access to sensitive data or inject malicious code into applications, leading to data breaches, system crashes, and other serious consequences.
APIs are a frequently targeted attack target. They often handle authentication tokens, personal data, payments, and backend services, making them appealing to attackers. Attackers favor APIs because they are predictable, highly automated, and often less protected than user-facing applications.
Failing to test APIs can result in:
Data breaches and regulatory violations
Account takeover and credential abuse
Unauthorized access to sensitive resources
Business logic abuse
Service degradation from automated abuse
What are the most common API security risks?
Many API vulnerabilities fall into well-known categories, including those outlined in the OWASP API Security Top 10. Common risks include:
No rate limiting. Systems allow for unlimited or high-frequency requests.
Broken authentication. Involves weak or improperly implemented token handling, JWT validation, or session management.
Broken authorization (IDOR). When users access objects or data they should not be allowed to see.
Business logic abuse. When legitimate workflows are used in unintended (nefarious) ways.
Excessive data exposure. When APIs return more data than necessary.
Injection attacks. When SQL, command, or NoSQL injection attacks occur.
Improper input validation. When APIs accept malformed or unexpected payloads.
What are API security testing best practices?
How to do API security testing
Strong API security testing should be applied throughout the API lifecycle. Best API security practices include efforts in the following areas.
Design and development
Follow secure API design standards (least privilege, schema validation)
Define authentication, authorization, and rate-limiting requirements early
Document endpoints and expected behavior clearly
Authentication and authorization testing
Test token expiration, revocation, and replay protection
Verify role-based and scope-based access controls
Attempt unauthorized access to protected resources
Input and schema validation
Test malformed requests, oversized payloads, and unexpected data types
Validate strict schema enforcement
Test for injection vulnerabilities
Abuse and automation testing
Simulate credential stuffing, enumeration, and scraping
Test rate limits and throttling behavior
Validate bot and anomaly detection effectiveness
Business logic testing
Attempt workflow manipulation to identify any weaknesses
Test edge cases and unexpected order of operations
How often should APIs be tested?
API security testing should be continuous. You should implement security testing:
During development and staging
Before every production release
Continuously in production environments
After change to authentication, endpoints, or data models (re-test)
How do bots affect API security testing?
Bots are responsible for a large percentage of API attacks. Testing should consider bot-driven scenarios like
High-rate automated requests
Credential stuffing attempts
Enumeration of IDs and parameters
Scraping and data harvesting
Simulating bot behavior ensures defenses work under real-world conditions.
What tools are used for API security testing?
Organizations typically use a mix of:
API scanners and fuzzers
Dynamic and interactive testing tools
Penetration testing platforms
Runtime protection and monitoring solutions
WAF, bot management, and edge security tools (like a CDN)
No single tool covers every risk. A layered approach to layered testing is key.
How do CDNs help with API security?
CDNs help secure APIs by enforcing protections at the edge, before traffic reaches backend services. This includes:
Rate limiting and request throttling
Bot detection and mitigation
IP and reputation-based filtering
Traffic anomaly detection
API security testing should validate how these edge controls interact with the API.
How Fastly can help
API security testing should be an ongoing effort. By combining secure design, continuous automated testing, manual validation, bot-aware abuse testing, and edge-based protection, organizations can significantly reduce the risk of API exploitation while maintaining performance and scalability.
Fastly API Security gives you the full picture of your API landscape. You can understand what exists, gain confidence that things are working as expected, and make targeted API abuse mitigation decisions across the Fastly platform.
Fastly’s Edge Cloud Platform inspects and filters API requests at its globally distributed edge locations. This means malicious or abusive traffic like bot-driven attacks, credential stuffing, or API scraping can be blocked or throttled before it ever reaches your application servers. Stopping threats early reduces backend load, lowers latency, and limits blast radius during attacks.