What are the potential security risks associated with not properly handling variables from the GET method in PHP?

Improperly handling variables from the GET method in PHP can lead to security vulnerabilities such as SQL injection, cross-site scripting (XSS), and other forms of attacks. To mitigate these risks, it is essential to properly sanitize and validate any data coming from the GET method before using it in your application.

// Example of properly handling variables from the GET method
$userId = isset($_GET['user_id']) ? intval($_GET['user_id']) : 0;

// Sanitize the input to prevent SQL injection
$userId = filter_var($userId, FILTER_SANITIZE_NUMBER_INT);

// Validate the input to ensure it meets the expected criteria
if($userId <= 0) {
    // Handle invalid user id
} else {
    // Proceed with using the sanitized and validated user id
}