Researchers at the cybersecurity firm Sansec have discovered a new type of malware that uses an innovative technique to inject payment card skimmer scripts into the checkout pages of compromised online stores.
The malware is able to hide in plain sight by using the social media buttons that now routinely appear at the bottom of websites to conceal its malicious payloads.
Sansec first spotted similar malware back in June though it was not nearly as sophisticated and was only detected on nine sites in a single day. However, of the infected sites, only one had functional malware as the others were missing a component that rendered the malware useless.
Hiding in plain sight
The payment skimmer malware discovered by Sansec use a double payload structure to help it avoid detection.
The malware’s creators hide the source code of the skimmer script in a social media sharing icon and a separate decoder is deployed somewhere else on an ecommerce’s site’s server which is used to extract and execute the credit card stealer.
In a blog post, Sansec provided further insight on how this new malware is able to avoid detection by using a novel technique, saying:
“This new malware has two parts: a concealed payload and a decoder, of which the latter reads the payload and executes the concealed code. While skimmers have added their malicious payload to benign files like images in the past, this is the first time that malicious code has been constructed as a perfectly valid image. The result is that security scanners can no longer find malware just by testing for valid syntax.”
We’ll likely hear more about this new malware once an easier way to detect and remove it from vulnerable ecommerce sites is discovered.