What are the potential pitfalls of coding tracking cookies in PHP?

One potential pitfall of coding tracking cookies in PHP is not properly sanitizing user input, which can leave the application vulnerable to attacks such as cross-site scripting. To mitigate this risk, always validate and sanitize user input before using it to set or read cookies.

// Validate and sanitize user input before setting cookie
$user_id = filter_var($_POST['user_id'], FILTER_SANITIZE_NUMBER_INT);
setcookie('user_id', $user_id, time() + 3600, '/');