Beneath the surface: Uncovering the shift in web skimming

Microsoft security researchers recently observed that web skimming campaigns now employ various obfuscation techniques to deliver and hide skimming scripts. It’s a shift from earlier tactics where attackers conspicuously injected malicious scripts into e-commerce platforms and content management systems (CMSs) via vulnerability exploitation, making this threat highly evasive to traditional security solutions. As of this writing, some of the latest skimming HTML and JavaScript files uploaded in VirusTotal have very low detection rates.

Web skimming typically targets platforms like Magento, PrestaShop, and WordPress, which are popular choices for online shops because of their ease of use and portability with third-party plugins. Unfortunately, these platforms and plugins come with vulnerabilities that the attackers have constantly attempted to leverage. One notable web skimming campaign/group is Magecart, which gained media coverage over the years for affecting thousands of websites, including several popular brands.

In one of the campaigns we’ve observed, attackers obfuscated the skimming script by encoding it in PHP, which, in turn, was embedded inside an image file—a likely attempt to leverage PHP calls when a website’s index page is loaded. Recently, we’ve also seen compromised web applications injected with malicious JavaScript masquerading as Google Analytics and Meta Pixel (formerly Facebook Pixel) scripts. Some skimming scripts even had anti-debugging mechanisms, in that they first checked if the browser’s developer tools were open.

Given the scale of web skimming campaigns and the impact they have on organizations and their customers, a comprehensive security solution is needed to detect and block this threat. Microsoft

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