Magento LTS Vulnerable to Open Redirect via Unvalidated `uenc` Parameter in `stockAction()`

Summary

Mage_ProductAlert_AddController::stockAction() reads the uenc query parameter and passes it directly to $this->_redirectUrl($backUrl) without calling $this->_isUrlInternal() When the supplied product_id does not match any catalog product, the server issues an unvalidated HTTP 302 redirect to whatever URL was provided as uenc.

Vulnerable path:

// app/code/core/Mage/ProductAlert/controllers/AddController.php : stockAction()

$backUrl = $this->getRequest()->getParam(Mage_Core_Controller_Front_Action::PARAM_NAME_URL_ENCODED);  // raw, no decode
$productId = (int) $this->getRequest()->getParam('product_id');

if (!$backUrl || !$productId) {
    $this->_redirect('/');
    return;
}

$product = Mage::getModel('catalog/product')->load($productId);

if (!$product->getId()) {
    $session->addError($this->__('Not enough parameters.'));
    $this->_redirectUrl($backUrl);   // ← NO _isUrlInternal() check
    return;
}

Secure peer (priceAction()):

if (!$product->getId()) {
    if ($this->_isUrlInternal($backUrl)) {  // ← validation present
        $this->_redirectUrl($backUrl);
    } else {
        $this->_redirect('/');
    }
    return;
}

Steps to Reproduce

Prerequisites

• OpenMage LTS ≤ 20.16.0 with Product Alerts enabled (default configuration)
• A valid, logged-in customer session on the target store

Step 1 – Authenticate as a Customer (Attacker controls the crafted link; victim must be logged in)

The preDispatch() hook calls Mage::getSingleton('customer/session')->authenticate($this). If the request comes from an unauthenticated user, they are redirected to the login page first. The open redirect only fires after the customer is authenticated. This is the realistic attack scenario: the attacker sends a crafted link to a customer who is already logged in.

<img width="1548" height="638" alt="image" src="https://github.com/user-attachments/assets/64c18279-ec0a-4110-b8f4-d952870e348c" />

Step 2 – Craft the Malicious URL

The uenc parameter is read raw via getParam() with no base64 decoding in this code path. A plain URL is sufficient and produces the redirect:

GET /productalert/add/stock/?product_id=99999&uenc=https://evil.com/steal-credentials HTTP/1.1
Host: <store-hostname>
Cookie: om_frontend=<authenticated-session>

Key conditions:

• product_id must reference a non-existent product (triggers the vulnerable branch; any large ID works)
• uenc is the raw destination URL (no base64 encoding required)

<img width="1554" height="852" alt="image" src="https://github.com/user-attachments/assets/d8530247-2d2f-4747-bf16-ece71a507b50" />

Impact

Technical Impact

An attacker who controls the uenc parameter value can redirect any logged-in shopper to an arbitrary external URL. Because the redirect originates from the legitimate store domain, the victim’s browser shows the trusted store URL in the address bar momentarily before being sent to the attacker site. The HTTP 302 response exits the store’s origin before the browser shows anything to the user.

Business-Level Attack Vectors

Propagation

A single malicious link can be embedded in:

• Customer emails (“Click here for stock notification preferences”)
• Forum posts, social media, or product reviews on the store
• SEO-poisoned search results that rank the store’s domain

Recommended Fix

Apply the same _isUrlInternal() guard used in priceAction() to the stockAction() missing-product

This is an AI-generated report.

An attempt was made to test the same PoC against the online demo https://demo.openmage.org/ but it couldn't be reproduced. It was only reproduced against the local setup env against the latest version.