API security protects the interfaces that connect your applications. As APIs handle more sensitive data and actions, securing them is critical.
OWASP API Security Top 10
- Broken object level authorization. Users access other users' data
- Broken authentication. Weak or broken authentication mechanisms
- Broken object property level authorization. Excessive data exposure
- Unrestricted resource consumption. No rate limits, DoS possible
- Broken function level authorization. Users access admin functions
- Unrestricted access to sensitive business flows. Automation abuse
- Server-side request forgery. Server makes unwanted requests
- Security misconfiguration. Default configs, verbose errors
- Improper inventory management. Old, unpatched, or unknown APIs
- Unsafe consumption of APIs. Trusting third-party APIs without validation
Authentication
- OAuth 2.0. Standard for delegated access
- API keys. For server-to-server, keep them secret and rotate
- JWT. Self-contained tokens with expiration
- Mutual TLS. Both client and server authenticate
- Never send credentials in URLs
Authorization
- Principle of least privilege. Minimum access needed
- Object-level authorization. Check ownership for every request
- Attribute-based access control. Fine-grained permissions
- Default deny. Allow only explicitly permitted actions
- Validate on the server. Never trust client-side checks
Input Validation
- Validate everything. Every parameter, every body
- Whitelist validation. Define what is allowed, reject the rest
- Sanitize. Remove or escape dangerous characters
- Schema validation. Check types, lengths, formats
- SQL injection prevention. Parameterized queries only
- XSS prevention. Escape output, set CSP headers
Rate Limiting
- Per user. Limit requests per authenticated user
- Per IP. Limit requests per IP address
- Per endpoint. Different limits for different endpoints
- Quota. Daily or monthly request limits
- Throttling. Slow down instead of hard stop
- 429 status. Return with Retry-After header
Transport Security
- HTTPS only. Redirect HTTP to HTTPS
- TLS 1.2+. Disable old protocols
- HSTS. Force HTTPS for future requests
- Certificate pinning. For mobile apps
Monitoring and Logging
- Log all requests. Method, path, user, timestamp, status
- Alert on anomalies. Spike in requests, unusual patterns
- Track errors. 4xx and 5xx rates
- Audit trail. Who did what, when
- Do not log sensitive data. Passwords, tokens, PII
Common API Vulnerabilities
- No rate limiting. Enables brute force and DoS
- Excessive data exposure. Returning more than the client needs
- No input validation. Enables injection attacks
- Broken access control. Users access other users' data
- No monitoring. Attacks go undetected
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