What are the potential risks of not properly sanitizing and validating user input in PHP applications, and how can they be mitigated?

Failure to properly sanitize and validate user input in PHP applications can lead to security vulnerabilities such as SQL injection, cross-site scripting (XSS), and remote code execution. This can result in unauthorized access to sensitive data, manipulation of the application's behavior, and potential compromise of the entire system. To mitigate these risks, it is essential to sanitize and validate all user input before using it in database queries, outputting to the browser, or executing any code.

// Sanitize and validate user input example
$user_input = $_POST['user_input'];

// Sanitize input to prevent SQL injection
$sanitized_input = mysqli_real_escape_string($connection, $user_input);

// Validate input to ensure it meets specific criteria
if (ctype_digit($sanitized_input)) {
    // Input is a valid digit, proceed with using it in the application
} else {
    // Input is not valid, handle the error accordingly
}