CVE-2026-42207

Magento Long Term Support (LTS) is an unofficial, community-driven project provides an alternative to the Magento Community Edition e-commerce platform with a high level of backward compatibility. Prior to 20.18.0, 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. This vulnerability is fixed in 20.18.0.

Magento Long Term Support (LTS) is an unofficial, community-driven project provides an alternative to the Magento Community Edition e-commerce platform with a high level of backward compatibility. Prior to 20.18.0, 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. This vulnerability is fixed in 20.18.0.

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

| Scenario | Description | |------------------------|-----------------------------------------------------------------------------| | Credential phishing | Craft a link claiming to show a stock notification. Customer lands on attacker’s login clone and reuses their password. | | OAuth / SSO token theft| If the store uses a social login or “Login with Google” flow, the attacker can inject their redirect_uri via the open redirect, stealing OAuth tokens. | | Affiliate fraud | Redirect customers from the legitimate store to a competing retailer after they click a “notify me” link. | | Malware distribution | Redirect to drive-by-download pages with the store’s reputation acting as social proof. |

Propagation

A single malicious link can be…

Magento Long Term Support (LTS) is an unofficial, community-driven project provides an alternative to the Magento Community Edition e-commerce platform with a high level of backward compatibility. Prior to 20.18.0, 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. This vulnerability is fixed in 20.18.0.

Magento Long Term Support (LTS) is an unofficial, community-driven project provides an alternative to the Magento Community Edition e-commerce platform with a high level of backward compatibility. Prior to 20.18.0, 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. This vulnerability is fixed in 20.18.0.

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

| Scenario | Description | |------------------------|-----------------------------------------------------------------------------| | Credential phishing | Craft a link claiming to show a stock notification. Customer lands on attacker’s login clone and reuses their password. | | OAuth / SSO token theft| If the store uses a social login or “Login with Google” flow, the attacker can inject their redirect_uri via the open redirect, stealing OAuth tokens. | | Affiliate fraud | Redirect customers from the legitimate store to a competing retailer after they click a “notify me” link. | | Malware distribution | Redirect to drive-by-download pages with the store’s reputation acting as social proof. |

Propagation

A single malicious link can be…