Guide
intermediate

Extension Security Checklist

Comprehensive security checklist for browser extension developers

Security Team
30 minutes
#security#checklist#audit#development

Extension Security Checklist

This comprehensive checklist helps developers ensure their browser extensions follow security best practices.

Pre-Development Checklist

Planning & Architecture

  • Define minimum required permissions - Only request what's absolutely necessary
  • Plan secure data flow - Map how data flows through your extension
  • Choose appropriate storage - Decide between local, sync, or encrypted storage
  • Design secure API communication - Plan HTTPS endpoints and authentication
  • Consider privacy implications - Assess data collection and user privacy

Development Checklist

Code Security

  • Input validation - Sanitize all user inputs
  • Output encoding - Prevent XSS attacks
  • Secure error handling - Don't expose sensitive information
  • Content Security Policy - Implement strong CSP headers
  • Avoid eval() and similar functions - Use safer alternatives
  • Secure JSON parsing - Handle JSON securely

Permission Management

  • Minimum permissions - Request only necessary permissions
  • Optional permissions - Use optional permissions where possible
  • Host permissions - Limit to specific domains
  • Permission explanations - Clearly explain why each permission is needed

Data Protection

  • Secure storage - Use appropriate storage mechanisms
  • Data encryption - Encrypt sensitive data at rest
  • HTTPS communication - Use TLS for all API calls
  • API authentication - Implement proper authentication
  • Data validation - Validate data from external sources

Testing Checklist

Security Testing

  • Static analysis - Run security scanning tools
  • Dynamic testing - Test extension in runtime
  • Penetration testing - Conduct security assessments
  • Dependency scanning - Check for vulnerable dependencies
  • Manual code review - Thorough code security review

Functional Testing

  • Permission testing - Test all permission scenarios
  • Data flow testing - Verify secure data handling
  • Error scenario testing - Test error conditions
  • Cross-browser testing - Test on target browsers
  • Performance testing - Ensure security doesn't impact performance

Deployment Checklist

Release Preparation

  • Code review completed - All code reviewed for security
  • Dependencies updated - All dependencies are latest secure versions
  • Vulnerability scan passed - No critical vulnerabilities found
  • Documentation updated - Security documentation is current
  • Privacy policy updated - Reflect current data practices

Store Submission

  • Manifest validation - Verify manifest is valid and secure
  • Permissions review - Double-check all permissions
  • Security disclosure - Document security measures
  • Privacy compliance - Ensure privacy policy compliance
  • Testing approval - All tests pass and documented

Post-Deployment Checklist

Monitoring & Maintenance

  • Security monitoring - Monitor for security issues
  • User feedback - Track security-related feedback
  • Dependency updates - Regularly update dependencies
  • Security patches - Promptly apply security updates
  • Incident response - Have a security incident response plan

Ongoing Security

  • Regular audits - Schedule periodic security audits
  • Penetration testing - Regular security assessments
  • Security training - Keep team updated on security practices
  • Threat monitoring - Monitor for new security threats
  • Compliance checking - Ensure ongoing compliance with standards

Common Security Issues to Check

XSS Prevention 

// ❌ Bad practice
element.innerHTML = userInput;

// ✅ Good practice
element.textContent = sanitizeInput(userInput);

Secure API Calls 

// ❌ Bad practice - HTTP
fetch('http://api.example.com/data');

// ✅ Good practice - HTTPS
fetch('https://api.example.com/data', {
	headers: { Authorization: 'Bearer token' }
});

Permission Requests 

// ❌ Bad practice - broad permissions
{
  "permissions": ["<all_urls>"],
  "host_permissions": ["<all_urls>"]
}

// ✅ Good practice - specific permissions
{
  "permissions": ["storage", "activeTab"],
  "host_permissions": ["https://example.com/*"]
}

Security Tools and Resources

  • Chrome Lighthouse - Performance and security audits
  • OWASP ZAP - Web application security testing
  • Retire.js - Vulnerable dependency detection
  • npm audit - Node.js security auditing

Security Resources

Conclusion

Regular use of this security checklist helps maintain robust security for browser extensions. Security is an ongoing process that requires continuous attention and improvement.

Remember to update this checklist as new security threats and best practices emerge.

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