// Vulnerable Code $quantity = $_GET['num']; // If user sends ?num=-5, this is accepted.
Even with proper casting, the num parameter can break business rules.
If you don't handle this correctly, your cart will simply overwrite the item instead of incrementing it, leading to a frustrating user experience. In this guide, we will break down how to create a robust add-cart.php
header('Content-Type: application/json'); echo json_encode(['success' => true, 'message' => 'Product added', 'cart_count' => array_sum(array_column($_SESSION['cart'], 'quantity'))]); add-cart.php num
Adding the same product with the same quantity twice should have the same net effect as adding it once with double the quantity. This is already covered by the logic that merges quantities, but ensure that you do not inadvertently create duplicate entries for the same product.
An attacker could trick a logged-in user into adding hundreds of items to their cart through hidden cross-site image links. Always embed a Cross-Site Request Forgery (CSRF) token inside your product forms and validate it inside add-cart.php before altering the user's session state. Server-Side Inventory Verification
. If not properly sanitized, it can lead to financial loss or system instability. ⚠️ Common Vulnerabilities Negative Quantities : Submitting // Vulnerable Code $quantity = $_GET['num']; // If
POST /add-cart.php HTTP/1.1 Host: example.com Content-Type: application/x-www-form-urlencoded Cookie: PHPSESSID=abc123
The Zen Cart vulnerability (CVE‑2006‑4214) allowed remote attackers to execute arbitrary SQL commands by manipulating the quantity field in the add_cart function. An attacker could modify the session, extract user data, or even corrupt the entire database.
In traditional PHP e-commerce applications, when a user clicks "Add to Cart," the browser sends a request to a backend script—often named add-cart.php . In this guide, we will break down how
add-cart.php?id=100&num=-999
https://vintage-books.com/add-cart.php?num=12
In most tutorials, such as those found on PHPpot , the logic follows this pattern: