Application Security Checklist: Essential Steps to Secure Your Code

When you're racing to meet deadlines and ship features, security can easily slip down your priority list. But we've all seen the headlines about data breaches and their aftermath – the reputation damage, the scrambling teams, the costly fixes. The good news is that preventing many common security issues doesn't require specialized expertise or massive time investments.

This practical application security checklist gives you the most important security controls to implement in your applications. I've organized it by category so you can tackle what matters most to your project first. This isn't an exhaustive security framework – it's a practical starting point that will eliminate the vast majority of common vulnerabilities.

Authentication And User Management

Nothing matters more than getting authentication right. It's your application's front door.

• Store passwords using modern hashing algorithms (bcrypt, Argon2, or PBKDF2)
• Enforce minimum password strength requirements
• Offer multi-factor authentication, especially for administrative accounts
• Generate strong, random session identifiers
• Invalidate sessions on logout and after periods of inactivity
• Use secure, HttpOnly cookies for session management
• Implement secure account recovery via time-limited links to verified emails
• Notify users of important account changes or recovery attempts

Access Control And Authorization

Getting authorization wrong can expose sensitive data or functionality to the wrong users.

• Give users only permissions they absolutely need; default to minimum access
• Verify permissions on every request, not just in the UI
• Check authorization for both functions and specific resources
• Use standard tokens (JWT, OAuth) with proper expiration and validation
• Regularly audit role assignments, especially administrative access

Input Validation And Output Encoding

Most attacks start with malicious input. Defend your application at every entry point.

• Validate all input server-side (client validation is convenience, not security)
• Use whitelist validation approaches that define what's allowed rather than what's blocked
• Use parameterized queries for all database operations
• Validate file uploads for content type, size, and name
• Encode user-supplied content before displaying it in the appropriate context
• Apply Content Security Policy (CSP) headers to prevent XSS attacks

Data Protection

Protecting sensitive data should be a top priority for any application.

• Use TLS/HTTPS for all traffic without exception
• Encrypt sensitive data at rest using industry-standard algorithms
• Implement proper key management – never hardcode encryption keys
• Minimize collection of sensitive data – don't store what you don't need
• Delete data when no longer needed for business or compliance purposes
• Mask or truncate sensitive data in logs and displays
• Set appropriate security headers (HSTS, X-Content-Type-Options, X-Frame-Options)
• Configure proper CORS policies to prevent unauthorized domain access

Error Handling And Logging

How your application fails can reveal as much to attackers as how it works.

• Display generic error messages to users while logging detailed errors server-side
• Prevent stack traces or technical details from being exposed to users
• Log security-relevant events like login attempts and permission changes
• Include contextual information in logs but avoid sensitive data
• Ensure logs are protected from unauthorized access
• Implement log rotation and retention policies

Third-Party Dependencies

Your application is only as secure as its weakest component.

• Set up automated scans for vulnerabilities in dependencies
• Establish a process to quickly update vulnerable components
• Only include libraries you genuinely need
• Use trusted sources and verify package integrity
• Pin dependency versions to prevent unexpected changes

Deployment And Infrastructure

Security doesn't stop with your code.

• Apply the principle of least privilege to services, accounts, and infrastructure access
• Keep all systems, services, and software up-to-date with security patches
• Implement proper network segmentation for sensitive components
• Secure source code repositories and limit access appropriately
• Control access to CI/CD systems and deployment pipelines
• Scan code and containers during the build process

Testing And Verification

Trust but verify your security controls.

• Add security-focused test cases to your testing suite
• Perform regular automated vulnerability scanning
• Test authentication and authorization controls specifically
• Verify that security headers are properly implemented
• Check encryption implementation with appropriate test cases
• Consider penetration testing for critical applications

Making This Checklist Work For You

This checklist isn't meant to be a one-time exercise. Here's how to make it truly effective:

1. Start early – Address security from the beginning of development
2. Prioritize based on risk – Focus first on authentication and protecting sensitive data
3. Automate where possible – Use tools to enforce security checks
4. Keep learning – Security is always evolving; stay informed about new threats

Remember that security isn't about achieving perfection – it's about significantly raising the bar for attackers while protecting your users' data and your business reputation.

Conclusion

Implementing this application security checklist won't make your application bulletproof, but it will eliminate the vast majority of common vulnerabilities that attackers exploit. The most important step is simply to start incorporating these practices into your development process.

Security doesn't have to be overwhelming. Start with the basics, focus on the highest risks first, and gradually build a more secure development practice.

Looking for additional layers of protection beyond what you can implement in code? EdgeOne's security services provide robust protection including DDoS protection and web protection capabilities that can catch many attacks before they ever reach your application. Start your free trial today to see how EdgeOne can complement your application security efforts with minimal configuration.