Researchers from Malwarebytes observed threat actors, likely Magecart Group 12, using this technique in attacks aimed at online stores running on Magento 1 websites.
“While performing a crawl of Magento 1 websites, we detected a new piece of malware disguised as a favicon. The file named Magento.png attempts to pass itself as ‘image/png’ but does not have the proper PNG format for a valid image file.” reads the analysis published by Malwarebytes.
In the latest attacks, the e-skimmer code is introduced into the online store dynamically at the server-side.
The web shell retrieves the e-skimmer from a remote host, the code involved in this attack is similar to a variant used in Cardbleed attacks documented by SanSec researchers in September.
The attribution of the attack to Magecart Group 12 is based on overlaps in TTPs observed in the attacks, experts also noticed that the domain name used in the attack (zolo[.]pw) is associated to the same IP address (217.12.204[.]185) as recaptcha-in[.]pw and google-statik[.]pw, domains previously associated with Magecart Group 12.
“In comparison, the skimmer we showed in this blog dynamically injects code into the merchant site. The request to the malicious domain hosting the skimming code is not made client-side but server-side instead. As such a database blocking approach would not work here unless all compromised stores were blacklisted, which is a catch-22 situation. A more effective, but also more complex and prone to false positives approach, is to inspect the DOM in real time and detect when malicious code has been loaded.”
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(SecurityAffairs – hacking, Magecart)