PHP is the backbone of millions of web applications, including popular frameworks like Laravel and Symfony. However, its popularity also makes it a frequent target. Securing your application starts with understanding how attackers exploit user input.

1. Use Prepared Statements (PDO)

**Never** concatenate user input directly into your SQL queries. This leaves you vulnerable to SQL Injection. Use PDO with prepared statements to separate the query structure from the user data.

// BAD: $pdo->query("SELECT * FROM users WHERE name = '" . $_GET['name'] . "'");
// GOOD:
$stmt = $pdo->prepare("SELECT * FROM users WHERE name = :name");
$stmt->bindParam(':name', $_GET['name']);
$stmt->execute();

2. Sanitize and Validate All User Input

Always validate input to ensure it meets expected criteria (e.g., email format, maximum length, integer type). Then, sanitize data that is displayed back to the user to prevent Cross-Site Scripting (XSS) attacks.

Use PHP functions like `filter_var()` for validation and `htmlspecialchars()` when rendering data to the browser to escape malicious HTML/JavaScript tags.

3. Secure Session Management

Ensure your session tokens are protected:

• Use secure cookies (`session.cookie_secure=1` in php.ini).
• Regenerate the session ID after successful login (`session_regenerate_id(true)`).