Web Security Best Practices

Application-level security guidance for WordPress (PHP), Laravel (PHP), Django (Python), FastAPI (Python), and Plotly Dash (Python/Flask).

Important

• Always treat user input as untrusted, including callback inputs in Dash
• Use framework security features instead of custom implementations
• Validate server-side even when client-side validation exists
• Fail securely — errors must not expose system details
• Keep dependencies updated and audited

OWASP Top 10 (2021)

The current OWASP Top 10 categories that this skill addresses:

1. A01 Broken Access Control — See references/authentication-csrf.md
2. A02 Cryptographic Failures — See references/secure-data-handling.md
3. A03 Injection — See references/sql-injection.md, references/xss-prevention.md
4. A04 Insecure Design — Apply defense in depth throughout
5. A05 Security Misconfiguration — See references/security-headers.md, references/environment-config.md
6. A06 Vulnerable Components — See references/security-testing.md (dependency auditing)
7. A07 Authentication Failures — See references/authentication-csrf.md, references/session-cookie-jwt.md
8. A08 Data Integrity Failures — See references/secure-data-handling.md
9. A09 Logging Failures — See references/environment-config.md
10. A10 SSRF — See references/api-security.md

When to Consult Each Reference

User is working on...	Load this reference
HTML output, templates, rendering user data	references/xss-prevention.md
Database queries, search, filters	references/sql-injection.md
Login, registration, forms, permissions, CSRF	references/authentication-csrf.md
HTTP headers, CORS, CSP, HSTS, iframe protection	references/security-headers.md
Sessions, cookies, JWT tokens, "remember me"	references/session-cookie-jwt.md
File uploads, downloads, media handling	references/file-upload-security.md
REST APIs, rate limiting, tokens, SSRF	references/api-security.md
PII, encryption, payment data, logging	references/secure-data-handling.md
.env files, secrets, debug mode, deployment	references/environment-config.md
Security testing, scanning, code review	references/security-testing.md

Code Review Quick Checklist

When reviewing any code for security, verify all of the following:

Input/Output: All user input sanitized before storage. All output escaped for context (HTML, JS, SQL, URL). No raw echo/print of user data.

Database: All queries use prepared statements, ORM, or parameterized queries. No string concatenation or f-strings in SQL.

Auth/Access: CSRF tokens on all state-changing forms. Permission checks before sensitive operations. No passwords or tokens in logs.

Headers: CSP, HSTS, X-Content-Type-Options, X-Frame-Options all set. CORS restricted to required origins only.

Sessions/Cookies: HttpOnly, Secure, SameSite flags on cookies. Session regenerated after login. JWT expiration enforced.

Files: Upload type, size, and content validated server-side. Filenames sanitized. Files stored outside web root.

API: Rate limiting on all public endpoints. Authentication on sensitive endpoints. Input validation on all parameters.

Config: No hardcoded secrets. Debug mode off in production. Error messages generic in production.

Dependencies: No known vulnerabilities in packages. Lock files committed. Audit tools configured.

Common Anti-Patterns

1. Trusting client-side validation alone — always validate server-side
2. Using blocklists instead of allowlists — prefer allowing known-good
3. Rolling your own crypto or auth — use proven libraries
4. Exposing detailed error messages in production
5. Ignoring framework security features that are available
6. Security through obscurity — hiding things is not protecting them
7. Not updating dependencies — known vulnerabilities get exploited fast
8. Storing sensitive data in client-accessible storage (localStorage, dcc.Store)