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API Security Testing


1. Authentication and Authorization

  • Authentication: Verify that the API correctly identifies users and applications accessing it.
    • OAuth/OAuth2: Ensure that OAuth flows are correctly implemented and tokens are securely handled.
    • JWT (JSON Web Tokens): Validate token generation, expiration, and revocation.
      • Use Strong Signing Algorithms
        • HS256, RS256, or ES256: Ensure you use strong algorithms like HS256 (HMAC with SHA-256) or RS256 (RSA with SHA-256) for signing your tokens.
        • Avoid Weak Algorithms: Avoid using weak or deprecated algorithms like HS256 with short keys.
      • Use HTTPS
        • Secure Transport: Always use HTTPS to prevent token interception during transmission. HTTPS ensures that the data, including JWTs, is encrypted during transmission.
      • Secure Storage
        • Client-Side Storage: Store JWTs securely in the client. Prefer storing them in memory rather than in local storage or session storage to mitigate the risk of XSS attacks.
        • HttpOnly Cookies: If you store JWTs in cookies, make sure they are HttpOnly to prevent JavaScript access, reducing the risk of XSS attacks.
      • Short Expiration Times
        • Limit Token Lifetime: Use short expiration times for JWTs to limit the window of exposure in case a token is compromised. Refresh tokens can be used to obtain new JWTs without requiring re-authentication.
      • Token Validation
        • Verify Signature: Always verify the token signature on the server to ensure it was issued by a trusted source.
        • Check Expiration: Validate the exp (expiration) claim to ensure the token has not expired.
        • Validate Claims: Check other claims like iss (issuer) and aud (audience) to ensure the token is valid for the specific context.
      • Use Refresh Tokens
        • Renew Access Tokens: Use refresh tokens to renew access tokens. This allows you to have short-lived access tokens while still maintaining a good user experience.
      • Revoke Tokens
        • Invalidate Tokens: Implement a mechanism to revoke tokens if they are compromised or no longer needed. This can be achieved by maintaining a token blacklist or using token versioning.
      • Implement Proper Scoping
        • Least Privilege: Include scopes in your JWTs to enforce the principle of least privilege. Ensure tokens have the minimum required permissions for the task.
      • Protect Against CSRF
        • Anti-CSRF Tokens: Use anti-CSRF tokens when storing JWTs in cookies to prevent Cross-Site Request Forgery attacks.
      • Monitor and Log
        • Audit Logs: Keep logs of token usage to detect unusual activity. Monitor for multiple invalid token attempts and take action if necessary.
      • Secure Secret Management
        • Environment Variables: Store secret keys in secure environment variables, not in your source code.
        • Key Rotation: Regularly rotate signing keys to minimize the impact of a compromised key.
      • Regular Security Audits
        • Penetration Testing: Regularly conduct security audits and penetration testing to identify and fix vulnerabilities in your JWT implementation.
  • Authorization: Ensure that authenticated users have the correct permissions to access specific resources.
    • Role-Based Access Control (RBAC): Verify that users can only perform actions that their roles permit.

2. Data Encryption

  • Transport Layer Security (TLS/SSL): Ensure that all API communications are encrypted using HTTPS.
  • Encryption at Rest: Verify that sensitive data stored in databases or files is encrypted.

3. Input Validation

  • SQL Injection: Test for vulnerabilities that could allow attackers to execute arbitrary SQL code.
  • Cross-Site Scripting (XSS): Ensure that the API correctly handles user input to prevent injection of malicious scripts.
  • Cross-Site Request Forgery (CSRF): Implement CSRF tokens to protect against unauthorized actions performed by authenticated users.

4. Rate Limiting and Throttling

  • Rate Limiting: Ensure that the API can limit the number of requests from a single user or IP address to prevent abuse.
  • Throttling: Implement throttling to manage the number of requests and control API usage patterns.

5. Error Handling and Logging

  • Error Messages: Ensure that error messages do not reveal sensitive information that could be used by attackers.
  • Logging: Implement logging of security-relevant events such as failed login attempts, access to restricted resources, and suspicious activities.

6. Security Headers

  • Content Security Policy (CSP): Prevent XSS attacks by defining which content sources are trustworthy.
  • Strict-Transport-Security (HSTS): Enforce HTTPS connections to the API.
  • X-Content-Type-Options: Prevent MIME-sniffing by setting this header to nosniff.
  • X-Frame-Options: Prevent clickjacking attacks by controlling whether your API endpoints can be embedded in iframes.

Security Tests

1. Authentication Tests

  • Valid Credentials: Send a request with valid credentials and verify access is granted.
  • Invalid Credentials: Send a request with invalid credentials and verify access is denied.
  • Expired Token: Use an expired token to access the API and ensure access is denied with an appropriate error message.
  • Token Tampering: Alter a valid token and check that the API detects the tampering and denies access.
  • No Authentication: Attempt to access protected endpoints without any authentication and verify access is denied.

2. Authorization Tests

  • Access with Correct Role: Verify that a user with the correct role can access specific resources.
  • Access with Incorrect Role: Check that a user with an incorrect role cannot access restricted resources.
  • Admin vs. User Access: Test endpoints to ensure that administrative actions cannot be performed by regular users.
  • Horizontal Access Control: Verify that users cannot access or modify resources owned by other users (e.g., another user's profile).

3. Input Validation Tests

  • SQL Injection: Send SQL commands in input fields to check for SQL injection vulnerabilities.
  • Cross-Site Scripting (XSS): Inject script tags into input fields to test if the API correctly sanitizes inputs.
  • Command Injection: Attempt to inject system commands in API requests to test for command injection vulnerabilities.
  • Boundary Testing: Test inputs with boundary values to check if the API properly handles edge cases (e.g., very large or very small inputs).

4. Rate Limiting and Throttling Tests

  • Burst Requests: Send a high number of requests in a short period to see if rate limiting is enforced.
  • Rate Limit Exceedance: Continue sending requests after the rate limit is reached and verify that the API responds with a 429 Too Many Requests status code.
  • IP Address Spoofing: Test if rate limiting is based on IP addresses and whether spoofing the IP can bypass limits.

5. Error Handling Tests

  • Invalid Input Data: Send requests with invalid or malformed data and verify that the API returns appropriate error messages without exposing internal details.
  • Unhandled Exceptions: Try to cause exceptions within the API to ensure it handles them gracefully and does not leak stack traces or sensitive information.

6. Session Management Tests

  • Session Fixation: Test if the session ID remains the same after login to check for session fixation vulnerabilities.
  • Session Timeout: Verify that sessions are appropriately timed out after a period of inactivity.
  • Simultaneous Sessions: Test if the same user can have multiple active sessions and how the API manages them.

7. Security Headers Tests

  • Content Security Policy (CSP): Verify that the CSP header is correctly configured to prevent XSS attacks.
  • X-Frame-Options: Check that the X-Frame-Options header is set to DENY or SAMEORIGIN to prevent clickjacking.
  • X-Content-Type-Options: Ensure the API sets the X-Content-Type-Options header to nosniff to prevent MIME-type sniffing.
  • Strict-Transport-Security (HSTS): Confirm that the HSTS header is present and correctly configured to enforce HTTPS.

8. Vulnerability Scanning and Penetration Testing

  • Automated Scans: Use tools like OWASP ZAP or Burp Suite to scan the API for common vulnerabilities.
  • Manual Penetration Testing: Conduct manual tests to discover potential vulnerabilities that automated tools might miss.

9. Sensitive Data Exposure Tests

  • Data Leakage: Ensure that sensitive data such as passwords, tokens, or personal information is not exposed in API responses.
  • Secure Storage: Verify that sensitive data is encrypted both in transit (using HTTPS) and at rest (using database encryption).

Test Cases

Test Case 1: SQL Injection

  • Description: Test if the API is vulnerable to SQL injection.
  • Steps:
    1. Send a request to the API with an SQL injection payload, such as ' OR '1'='1.
    2. Observe the API response and logs.
  • Expected Result: The API should sanitize the input and return an error or handle the input gracefully without executing the injected SQL command.

Test Case 2: XSS

  • Description: Test if the API is vulnerable to cross-site scripting.
  • Steps:
    1. Send a request with a payload containing a script tag, such as <script>alert('XSS')</script>.
    2. Check the API response for script execution or sanitization.
  • Expected Result: The API should sanitize the input and prevent the script from being executed.

Test Case 3: Rate Limiting

  • Description: Test the rate limiting mechanism of the API.
  • Steps:
    1. Send a large number of requests to the API within a short time frame.
    2. Continue sending requests after hitting the rate limit.
  • Expected Result: The API should respond with a 429 Too Many Requests status code after the rate limit is exceeded.