Advisory: Shopware Cart Accessible by Third-Party Websites

RedTeam Pentesting discovered that the shopping cart implemented by Shopware
offers an insecure API. Malicious, third-party websites may abuse this API to
list, add or remove products from a user's cart.


Details
=======

Product: Shopware
Affected Versions: 4.0.1 - 5.3.7
Fixed Versions: > 5.4.0
Vulnerability Type: Cross-Site Request Forgery
Security Risk: low
Vendor URL: https://shopware.com
Vendor Status: fixed version released
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2017-012
Advisory Status: published
CVE: GENERIC-MAP-NOMATCH
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=GENERIC-MAP-NOMATCH


Introduction
============

"Shopware 5 is the next generation of open source e-commerce software made in
Germany. Based on bleeding edge technologies like Symfony 2, Doctrine 2 & Zend
Framework Shopware comes as the perfect platform for your next e-commerce
project. Furthermore Shopware 5 provides an event-driven plugin system and an
advanced hook system, giving you the ability to customize every part of the
platform."
(from the Shopware GitHub repository [1])


More Details
============

The Shopware web application provides users with a virtual shopping cart to
collect products prior to checkout. This cart is displayed to the user as a
modal sidebar appearing at the right edge of the browser window. Consequently,
Shopware implements several API endpoints to allow JavaScript code to perform
shopping cart operations. These endpoints are implemented in the
"Shopware_Controllers_Frontend_Checkout" class and can be reached through the
following paths:

 * /checkout/ajaxCart
 * /checkout/ajaxAddArticleCart
 * /checkout/ajaxDeleteArticleCart

RedTeam Pentesting discovered that API endpoints support JSONP by specifying a
URL parameter named callback. The origin of calls to the cart API is not
validated. Therefore, any third-party website may make use of this API. If a
customer of a Shopware shop visits a malicious, attacker-controlled website,
JavaScript code on this site may access the user's shopping cart.


Proof of Concept
================

The following JavaScript snippets demonstrate how to access the cart of a
Shopware shop at "https://example.net" from a third-party website. The
"getJSON" function of jQuery 3 is used to interface with the JSONP API.

By running the following code, the contents of a cart may be retrieved. The
result of the API call is displayed on the browser's developer console.

------------------------------------------------------------------------
$.getJSON("https://example.net/checkout/ajaxCart?callback=?")
.done(console.log);
------------------------------------------------------------------------

The following code adds a new product to the cart. In this case, two instances
of product 1234 are added.

------------------------------------------------------------------------
$.getJSON(
  "https://example.net/checkout/ajaxAddArticleCart"+
  "?callback=?&sAdd=1234&sQuantity=2"
).done(console.log);
------------------------------------------------------------------------

To remove a product from a user's shopping cart, attackers may use the
following code. An id for the "sDelete" parameter may be obtained through a
prior call to ajaxCart.

------------------------------------------------------------------------
$.getJSON(
  "https://example.net/checkout/ajaxDeleteArticleCart"+
  "?callback=?&sDelete=4321"
).done(console.log);
------------------------------------------------------------------------


Workaround
==========

Support for JSONP should be removed from the cart AJAX API. This ensures, that
only JavaScript code from the same origin may access the API and respectively
the cart's contents. Furthermore, operations which change the state of the cart,
i.e. adding and removing products, must be protected with CSRF tokens.


Fix
===

Upgrade to Shopware newer than 5.4.0.


Security Risk
=============

This vulnerability is rated as a low risk. Disclosure of a user's shopping cart
to attackers may negatively impact the user's privacy. Furthermore, competing
eCommerce sites may use this information to improve sales. By adding or
removing products from a user's cart, attackers can negatively impact a user's
shopping experience and create support effort for the shop operator.


Timeline
========

2017-08-28 Vulnerability identified
2017-09-13 Customer approved disclosure to vendor
2017-09-14 Vendor notified
2018-02-27 Vendor released fixed version
2018-03-13 Advisory released


References
==========

[1] https://github.com/shopware/shopware
[2] https://community.shopware.com/Downloads_cat_448.html#5.4.0


RedTeam Pentesting GmbH
=======================

RedTeam Pentesting offers individual penetration tests performed by a
team of specialised IT-security experts. Hereby, security weaknesses in
company networks or products are uncovered and can be fixed immediately.

As there are only few experts in this field, RedTeam Pentesting wants to
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security-related areas. The results are made available as public
security advisories.

More information about RedTeam Pentesting can be found at:
https://www.redteam-pentesting.de/


Working at RedTeam Pentesting
=============================

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