New Caesar Cipher Card Skimmer Lurks in WordPress, Magento, and OpenCart

Written by Lore Apostol
Published on June 21, 2024

A new variation of the “gtag” credit card skimming attack impacted almost 80 sites in the first two weeks after its discovery, a new Sucuri report says. Called Caesar Cipher Skimmer, this new malware was deployed to several different CMS platforms, infecting WordPress, Magento, and OpenCart. 

The security researchers and analysts focused on a case where the card information stealer infected the WordPress WooCommerce plugin, triggering their antivirus program on their computer while on the website’s checkout page due to the suspicious code injected in the ‘form-checkout.php’ script.

Skimming Malware WordPress
Image Source: Succuri

Lately, the injections have changed to look less suspicious than a long obfuscated script. They pretend to be simultaneously the Google Analytics and Google Tag Manager plugins, using String.fromCharCode to obfuscate their code. 

The malware uses techniques like splitting the string into individual characters, reversing the character order, subtracting by three and converting back the character code of each character's Unicode value, and joining the characters back into a string to hide its payload – essentially using a Caesar Cipher on the Unicode values rather than letters.

Infected WordPress Plugin Code
Image Source: Succuri

The scripts load an extra layer that creates a WebSocket to a URL and connects to a remote server that sends another layer of the skimmer. This second layer sometimes checks if a logged-in WordPress user loads it and sends a customized response for each infected site. Older versions of the second layer contain code in Russian.

In some cases, the attackers also leveraged the ‘Insert Headers and Footers WPCode’ plugin to inject the malware into the website database, which other malicious actors have employed to add server-side redirects within website code.

Credit card skimming JavaScript is often found in the ‘core_config_data’ database table on Magento websites, which stores custom code inserted into the Magento admin.

For a better user experience we recommend using a more modern browser. We support the latest version of the following browsers: For a better user experience we recommend using the latest version of the following browsers: