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Fake payment page before checkout on Shopify and BigCommerce

A garanteed safe checkout with paypal, etc, on Shopify
A new type of web skimmer was found on a dozen stores hosted on Shopify, BigCommerce, Zen Cart and WooCommerce. Hosted (SaaS) ecommerce platforms like BigCommerce and Shopify do not allow custom JavaScript on their checkout pages. This skimmer evades that by showing a fake payment form and recording customer keystrokes before they enter the actual checkout page.

Once the data is intercepted and exfiltrated, the attackers display an error message and the customer is redirected to the real payment page. Customers probably just enter their details again and it takes several days/weeks before they notice they’ve been charged twice.

A fake payment page, just like the regular Paypal checkout

Sorry, Paypal Checkout failed processing your order. You will be redirected to Shopify Checkout.

A rare attack on multiple ecommerce platforms

It is remarkable that so many different platforms are compromised in the same campaign. Typically, criminals exploit a flaw in a single platform. Attackers may have breached a shared component, a piece of software or a service that is used by all affected merchants over the different ecommerce platforms.

Another curious technique is that this skimmer uses programmatically generated exfiltration domains. It keeps a counter and uses base64 encoding to produce a new domainname:

Skimmer using programmatically generated exfiltration domains

This will lead to, for example, these exfiltration domains. The first one was registered on August 31st.

zg9tywlubmftzw5ldza.com
zg9tywlubmftzw5ldze.com
zg9tywlubmftzw5ldzu.com
zg9tywlubmftzw5ldzq.com
zg9tywlubmftzw5ldzm.com
zg9tywlubmftzw5ldzy.com
zg9tywlubmftzw5ldzi.com
zg9tywlubmftzw5ldzg.com
zg9tywlubmftzw5ldzk.com
zg9tywlubmftzw5ldzez.com
zg9tywlubmftzw5ldzex.com
zg9tywlubmftzw5ldzew.com
zg9tywlubmftzw5ldzey.com
zg9tywlubmftzw5ldze0.com
zg9tywlubmftzw5ldze1.com

Exfiltration domain visible in the developer window

Here is an example of how the raw malware is hidden in the ecommerce websites:

The raw malware code is hidden in the page source code

SaaS ecommerce platforms and security

This campaign shows that platforms are no boundary to the profitable fraud of web skimming or formjacking. Wherever customers enter their payment details, they are at risk. Merchants should implement measures to actively counter this.

With SaaS ecommerce platforms the merchant has no option to add a security scanner to look for malicious JavaScript or other malware. One approach to mitigate these forms of attacks is by educating customers (“Notify us when witnessing any strange behavior, like errors during your checkout”) and instructing support staff to be on the lookout for these subtle signs (”A few customers reported trouble checking out.”)

Please contact Sansec if you think an attacker has added a fake payment form to your ecommerce website.

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