Defining the Scope of API Security Assessment

Before API release, conduct a targeted security assessment covering all components: entry points, request processing, data stores, and logging mechanisms. The assessment scope should encompass core functionality, edge cases, error handling, and inter-service communication. Define which API endpoints are in scope, which data types they handle, and which threat models are most relevant to your deployment environment.

OWASP Top 10 establishes industry-recognized critical security risks for web applications and provides a standardized approach to identifying them. Adopting this reference standard as the foundation for your assessment ensures focus on the most impactful vulnerabilities and helps establish a secure development culture within your organization.

    Verification of Authentication Mechanisms and Token Management

    Ensure your API implements robust authentication mechanisms: JWT tokens must use cryptographically strong signature algorithms, possess short lifetimes (15-60 minutes), and be generated securely. Verify that refresh tokens are stored safely, have longer expiration times than access tokens, and undergo regular rotation. Test the complete authentication flow including initial login, token refresh, and session termination.

    Conduct testing to detect credential leakage in logs, URL parameters, and headers. Verify the API does not return sensitive data (passwords, tokens) in error responses. Test token revocation mechanisms to ensure expired or revoked tokens genuinely block resource access. Validate that token claims are verified server-side and that client-side claims are never trusted without verification.

    • Test attempts to use expired or invalid tokens
    • Verify absence of hard-coded credentials in source code and configuration files
    • Validate token expiration and timestamp verification on server-side

    Validation of Authorization Mechanisms and Access Control

    Verify that each API endpoint has explicit authorization rules and users cannot access other users' resources through ID parameter manipulation. Ensure role-based access control (RBAC) or attribute-based access control (ABAC) is properly implemented and authorization checks occur server-side, never client-side only. Test authorization across all API paths, query parameters, and request body fields that reference resources.

    Conduct testing for horizontal privilege escalation (accessing other users' resources) and vertical privilege escalation (attempting to gain administrative rights). Ensure different user roles cannot perform unauthorized actions and the system logs all unauthorized access attempts. Verify that permission checks cannot be bypassed through direct API calls or parameter modification.

    • Test RBAC/ABAC functionality across all endpoints with multiple role combinations
    • Test edge cases: empty roles, missing permissions, conflicting permissions
    • Verify authorization cannot be circumvented through direct API access or cached credentials

    Input Validation and Injection Attack Prevention

    Implement whitelist-based validation of all inputs instead of blacklist approaches. All parameters, headers, and request bodies must be validated for type, length, format, and content before processing. Use parsers that automatically reject unexpected data formats (e.g., strict JSON or XML parsing). Define clear schemas for all API requests and enforce strict adherence to these schemas.

    Test protection against SQL injection, command injection, XPath injection, and LDAP injection attacks. Verify that parameterized queries or prepared statements are used for all database operations. Check handling of special characters, Unicode sequences, and encoded data (base64, URL-encoding). Conduct boundary value testing with extremely long strings, null bytes, and malformed data.

    • Test SQL injection vectors through query parameters, path segments, and request bodies
    • Verify proper handling of null bytes, newline characters, and special characters
    • Validate file upload size limits, type restrictions, and content scanning if file operations are supported

    Sensitive Data Protection and Encryption

    Ensure all communication between client and server uses HTTPS with TLS 1.2 or higher. Verify that certificates are valid, not expired, and signed by a trusted certificate authority. Ensure the API does not allow unencrypted HTTP connections and properly enforces HTTPS redirection. Test for certificate pinning if appropriate for your threat model and verify certificate validation cannot be bypassed.

    Verify that sensitive data (personally identifiable information, passwords, payment credentials) is not logged, cached, or stored in plaintext. Ensure passwords are hashed using modern algorithms (bcrypt, scrypt, Argon2) with proper salt. Data at rest must be encrypted if it contains confidential information. Implement field-level encryption for highly sensitive data elements.

    • Verify TLS version and configuration on server endpoints
    • Scan codebase for logging of sensitive data elements
    • Verify correct cryptographic functions are used for password hashing and data encryption

    Error Handling, Logging, and Security Monitoring

    The API must return appropriate HTTP status codes (400 for client errors, 500 for server errors) without exposing internal system details. Error messages must not disclose database structure, file paths, library versions, or other technical information useful to attackers. Use generic error messages for end-users while maintaining detailed logging for administrators. Implement separate error responses for authentication failures, authorization failures, and input validation failures.

    Ensure all significant events (authentication attempts, authorization decisions, data modifications, security exceptions) are recorded in logs with timestamps, user identifiers, and source IP addresses. Logs must be stored securely and protected from unauthorized access and modification. Implement alerting for suspicious activities such as repeated failed authentication attempts, unauthorized access attempts, or unusual data access patterns.

    • Verify absence of stack traces in error responses returned to clients
    • Confirm all authentication attempts (successful and failed) are logged
    • Check that logs do not contain user passwords, tokens, or other credentials

    Testing Methodology and Pre-Release Verification Planning

    Use standardized testing methodologies such as those described in NIST SP 800-115 and OWASP Web Security Testing Guide. These frameworks provide practical recommendations for planning, implementing, and maintaining technical security test processes. Before release, conduct both automated vulnerability scanning and manual testing, focusing on application logic, complex interaction scenarios, and authorization boundaries.

    Create a comprehensive test plan covering all API endpoints, different user roles, edge cases, and failure scenarios. Testing should include functional verification (code returns correct results), security testing (system is protected from exploitation), and performance testing (system remains stable under load). Document all identified security issues, their severity classification, and remediation status before final release. Establish a process for tracking security findings and their resolution.

    • Use OWASP Top 10 as the foundation for prioritizing security checks
    • Combine automated scanning tools with manual code analysis and logic testing
    • Create explicit test cases for each identified threat scenario

    Sources

    PENTEST.RED / RED JOURNAL