Application Security Best Practices

Input Validation

• Validate all user input
• Use allowlisting over blocklisting
• Sanitize HTML to prevent XSS
• Use parameterized queries for SQL
• Validate file uploads (type, size)

Authentication

• Use strong password hashing (bcrypt, argon2)
• Implement MFA where possible
• Use secure session management
• Implement rate limiting on auth endpoints
• Use JWTs properly (short expiry, refresh tokens)

Authorization

• Implement least privilege
• Check authorization on every request
• Use role-based access control
• Implement row-level security
• Audit access to sensitive data

Data Protection

• Encrypt sensitive data at rest
• Use TLS for data in transit
• Don't log sensitive data
• Implement proper key management
• Use secure cookie flags

Common Vulnerabilities (OWASP Top 10)

• Injection: Use prepared statements
• Broken Auth: Secure session handling
• XSS: Sanitize output, use CSP
• CSRF: Use anti-CSRF tokens
• Security Misconfiguration: Review defaults
• Sensitive Data Exposure: Encrypt everything
• Broken Access Control: Check on server
• SSRF: Validate URLs, use allowlists

Dependencies

• Keep dependencies updated
• Use npm audit/pip audit
• Pin dependency versions
• Use lockfiles
• Monitor for vulnerabilities