A new credit card web skimmer, known as the Caesar Cipher Skimmer, has recently targeted major content management systems (CMS) like WordPress, Magento, and OpenCart. This skimmer malware is injected into e-commerce sites with the primary goal of stealing payment and financial information. According to Sucuri, the attack involves malicious modifications to the checkout PHP file of the WooCommerce plugin for WordPress, disguising the malware as Google Analytics or Google Tag Manager to avoid detection.
The Caesar Cipher Skimmer uses a substitution mechanism similar to the Caesar cipher to encode the malicious code into a garbled string, concealing the external domain that hosts the payload. Previously compromised websites are likely exploited through PHP scripts named “style.css” or “css.php” to mimic HTML style sheets and evade detection. These scripts then load obfuscated JavaScript code that creates a WebSocket connection to a remote server to fetch the actual skimmer.
The malware’s sophisticated approach includes sending the URL of the infected web pages, allowing attackers to customize responses for each site. Some versions of the skimmer even modify the response if loaded by a logged-in WordPress user, adding another layer of stealth. Notably, comments in some versions of the script are written in Russian, suggesting that the threat actors may be Russian-speaking.
In addition to the WooCommerce plugin, the skimmer has been found injected into legitimate plugins like WPCode and into database tables in Magento sites. The prevalence of WordPress and its plugins as a foundation for many websites makes it a prime target for such attacks. Site owners are advised to keep their CMS software and plugins updated, enforce strong password practices, and regularly audit their sites for suspicious activity.
Reference:
