Web application vulnerabilities remain one of the most common attack vectors for businesses. Whether you build customer portals, SaaS platforms, or internal tools, applying these ten security practices significantly reduces your risk of a breach.
1. Validate All Input
Never trust data from users, APIs, or external systems. Validate input on the server side — not just the client. Check data types, lengths, ranges, and formats. Reject anything that does not match expected patterns. This single practice prevents entire classes of attacks including SQL injection, XSS, and command injection.
2. Implement Proper Authentication
Authentication is the front door to your application. Get it right:
- Enforce multi-factor authentication (MFA) for all user accounts, especially admin roles
- Use established authentication libraries and frameworks — never build your own
- Hash passwords with bcrypt, scrypt, or Argon2 — never store them in plain text
- Implement account lockout policies after failed login attempts
- Use secure session management with HttpOnly, Secure, and SameSite cookie flags
3. Apply the Principle of Least Privilege
Every user, service account, and API key should have only the minimum permissions needed to perform its function. If a component is compromised, least privilege limits the blast radius. Apply this principle to database access, API endpoints, file system permissions, and cloud service roles.
4. Encrypt Data in Transit and at Rest
Use TLS 1.3 for all communications — not just login pages, but every request. Encrypt sensitive data at rest in your database and file storage. Manage encryption keys securely using a dedicated key management service rather than hardcoding them in application code.
5. Prevent Cross-Site Scripting (XSS)
XSS attacks inject malicious scripts into your application that run in other users' browsers. Prevent them by:
- Encoding all output rendered in HTML, JavaScript, CSS, and URL contexts
- Using Content Security Policy (CSP) headers to restrict script sources
- Avoiding innerHTML and similar dangerous DOM manipulation methods
- Using modern frameworks (React, Next.js) that auto-escape output by default
6. Secure Your Dependencies
Third-party libraries and packages are a major attack vector. Open-source dependencies can contain known vulnerabilities or be compromised through supply chain attacks. Integrate dependency scanning into your DevSecOps pipeline to automatically flag vulnerable packages, and keep dependencies up to date.
7. Implement Proper Error Handling
Application errors can leak sensitive information to attackers — database structures, file paths, stack traces, or API keys. Use generic error messages for users and log detailed errors securely on the server. Never expose stack traces or internal system details in production responses.
8. Add Security Headers
HTTP security headers provide defense-in-depth with minimal implementation effort:
- Content-Security-Policy — restricts script and resource sources
- X-Content-Type-Options: nosniff — prevents MIME type sniffing
- X-Frame-Options: DENY — prevents clickjacking attacks
- Strict-Transport-Security — enforces HTTPS connections
- Referrer-Policy — controls referrer information leakage
- Permissions-Policy — restricts browser feature access
9. Log and Monitor Security Events
You cannot detect attacks if you are not watching. Log authentication events, access control failures, input validation errors, and application exceptions. Send logs to a centralized system and set up alerts for suspicious patterns. This capability is also a requirement under NIS2 for organizations in scope.
10. Test Regularly
Security is not a one-time effort. Integrate security testing throughout your development lifecycle:
- Automated scanning — run SAST and DAST tools in your CI/CD pipeline on every build
- Penetration testing — conduct regular penetration tests to find vulnerabilities that automated tools miss
- Code reviews — include security-focused code review as part of your development process
- Dependency audits — regularly check for and remediate vulnerable dependencies
How ICTLAB Can Help
ICTLAB helps development teams build secure web applications from the ground up. Our web development team follows these security practices by default, and our cybersecurity team provides penetration testing and security assessments to validate your application's defenses. Whether you need a security review of an existing application or want to build a new one with security embedded from day one, our Brussels-based team is ready to help.