Blog | G5 Cyber Security

Cloud API Risk Assessment: A Practical Guide

G5 Cyber Security

TL;DR

Assessing risks for cloud APIs involves understanding what data it handles, who can access it, and how secure the underlying platform is. This guide covers practical steps using common standards like OWASP and NIST to help you identify vulnerabilities and protect your API.

1. Understand Your API & Data

  1. Data Classification: What type of data does your API process? (e.g., Personally Identifiable Information – PII, financial details, health records). This determines the level of protection needed.
    • Categorise data sensitivity: Public, Internal, Confidential, Restricted.
    • Document where each data type is stored and processed within the API lifecycle.
  2. API Functionality Mapping: List every function your API performs. This helps pinpoint potential attack surfaces.
    • Create a detailed inventory of all endpoints (URLs).
    • Document input and output parameters for each endpoint.
  3. Data Flow Diagram: Visualise how data moves through your API, including interactions with other services.
    • Identify all third-party integrations.
    • Note any external dependencies.

2. Threat Modelling

  1. STRIDE Model: Use STRIDE (Spoofing, Tampering, Repudiation, Information Disclosure, Denial of Service, Elevation of Privilege) to identify potential threats.
    • For each API function, consider how an attacker could exploit it using each STRIDE category.
    • Document the likelihood and impact of each threat.
  2. OWASP Top 10: Focus on common web application security risks relevant to APIs.
    • Injection: Prevent SQL, NoSQL, and command injection vulnerabilities through input validation and sanitisation.
    • Broken Authentication: Implement strong authentication mechanisms (e.g., OAuth 2.0) and multi-factor authentication where appropriate.
    • Sensitive Data Exposure: Protect sensitive data in transit and at rest using encryption.
    • XML External Entities (XXE): Disable external entity processing if you use XML.

3. Security Controls & Testing

  1. Authentication & Authorisation: Implement robust access controls.
    • Use API keys, OAuth 2.0, or JWT (JSON Web Tokens).
    • Enforce least privilege – grant users only the permissions they need.
  2. Input Validation: Validate all input data to prevent injection attacks. 
    # Example Python validation snippet
    def validate_input(data):
  if not isinstance(data, str):
    return False
  if len(data) > 255:
    return False
  return True
  3. Rate Limiting: Protect against Denial of Service (DoS) attacks. 
    # Example Nginx rate limiting configuration
    limit_req_zone $binary_remote_addr zone=mylimit:10m rate=5r/s; 

server {
  location /api/{
    limit_req zone=mylimit burst=10;
  }
}
  4. Encryption: Use TLS (Transport Layer Security) for all API communication.
  5. API Gateway: Consider using an API gateway to manage security, routing, and monitoring.
  6. Vulnerability Scanning: Regularly scan your API code and infrastructure for vulnerabilities.
    • Use tools like OWASP ZAP or Burp Suite.
    • Automate scanning as part of your CI/CD pipeline.
  7. Penetration Testing: Engage a third-party to perform penetration testing.

4. Compliance & Standards

  1. NIST Cybersecurity Framework: Provides a structured approach to managing cyber security risks.
    • Identify, Protect, Detect, Respond, Recover – map your API security controls to these functions.
  2. PCI DSS (Payment Card Industry Data Security Standard): If handling credit card data, you *must* comply with PCI DSS.
  3. GDPR (General Data Protection Regulation) / UK GDPR: If processing personal data of EU citizens, comply with GDPR requirements.
    • Data minimisation, purpose limitation, storage limitation.
  4. HIPAA (Health Insurance Portability and Accountability Act): If handling protected health information (PHI), you must comply with HIPAA regulations.

5. Ongoing Monitoring & Improvement

  1. Logging & Auditing: Log all API requests and responses for auditing purposes.
  2. Incident Response Plan: Have a plan in place to respond to security incidents.
  3. Regular Reviews: Regularly review your API security controls and update them as needed.
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