What are the potential pitfalls of not defining input fields for variables in PHP forms?

The potential pitfalls of not defining input fields for variables in PHP forms include security vulnerabilities such as SQL injection attacks and the possibility of receiving unexpected or malicious input from users. To solve this issue, it is important to always define the input fields for variables in PHP forms by using functions like htmlspecialchars() to sanitize user input and prevent potential security risks.

// Define input fields for variables in PHP form
$name = isset($_POST['name']) ? htmlspecialchars($_POST['name']) : '';
$email = isset($_POST['email']) ? htmlspecialchars($_POST['email']) : '';
$message = isset($_POST['message']) ? htmlspecialchars($_POST['message']) : '';