PHP Security

Priority: P0 (CRITICAL)

Structure

src/
└── Security/
    ├── Validators/
    └── Auth/

Implementation Guidelines

• Prepared Statements: Use PDO with Parameterized Queries: $stmt = $pdo->prepare('SELECT * FROM users WHERE id = :id'); $stmt->execute([':id' => $id]);. NEVER concatenate user input into SQL strings.
• Password Hashing: ALWAYS use password_hash() with PASSWORD_ARGON2ID (PHP 7.4+) or PASSWORD_BCRYPT.
• Auth Verification: Use password_verify(). Use password_needs_rehash() to upgrade legacy hashes. Implement Rate Limiting and MFA where appropriate.
• XSS Escaping: Use htmlentities($userInput, ENT_QUOTES | ENT_HTML5, 'UTF-8') or htmlspecialchars() on all user output. Prefer Twig or Blade for auto-escaping.
• CSRF Protection: Mandate CSRF tokens for all state-changing requests (POST, PUT, PATCH, DELETE).
• Input Validation: Use filter_var($email, FILTER_VALIDATE_EMAIL) or filter_var($url, FILTER_VALIDATE_URL). Always Whitelist allowed values.
• File Security: RESTRICT file uploads by MIME type and extension. Store uploads outside the public root.
• Session Safety: Configure session.cookie_httponly = 1, session.cookie_secure = 1, and session.samesite = "Lax".
• Header Security: Enforce Content-Security-Policy (CSP), X-Frame-Options: DENY, and X-Content-Type-Options: nosniff.

Anti-Patterns

• No SQL string concatenation: Use PDO prepared statements only.
• No MD5/SHA1 for passwords: Use password_hash($password, PASSWORD_ARGON2ID).
• No raw $_GET/$_POST: Validate all input with filter_var() first.
• No production error display: Log to file; never show to users.

References

• Secure Implementation Patterns