If you currently have add-cart.php?num= in production, stop reading and go audit it now. Your users’ data—and your business—depend on it.
$product_id = filter_input(INPUT_POST, 'product_id', FILTER_VALIDATE_INT, ['options' => ['min_range' => 1]]); $quantity = filter_input(INPUT_POST, 'quantity', FILTER_VALIDATE_INT, ['options' => ['min_range' => 1, 'max_range' => 99]]); if (!$product_id || !$quantity) http_response_code(400); die('Invalid request');
Never trust user input. Always validate data types. Never use GET requests to modify state. And for the love of security, move away from raw add-cart.php scripts and toward modern, token-authenticated POST endpoints.
$stmt = $conn->prepare("SELECT price, stock FROM products WHERE id = ? AND active = 1"); $stmt->bind_param("i", $product_id); $stmt->execute(); Principle 4: Implement CSRF Tokens Since you are modifying state (the cart), every request must include a unique token.
A request to add-cart.php?num=1.1 returns a MySQL error: "Unknown column '1.1' in 'where clause'" — SQL injection confirmed.