A Magento plugin vulnerability that dates back at least three years could allow e-skimming attacks on unsuspecting online shoppers, the FBI warns.

In an alert sent out earlier this month, the FBI said hackers are using the exploit to take over e-commerce stores powered by Magento software and steal payment card data from customers.

The attacks work by embedding malware into Magento Mass Import, also known as MAGMI. The cross-site scripting bug allows cybercriminals to infect an online store’s HTML code to conduct e-skimming without being noticed.

How Malware Targets MAMGI

Any time someone buys from an e-commerce store using the Magento plugin, hackers can record details of the financial transaction after modifying the site’s PHP and JavaScript files.

The FBI said those who know how to exploit the bug are also planting web shells to allow them access to the same store again. While an e-commerce shop owner might not be aware, the stolen data is sent to the cybercriminals’ command-and-control (C&C) server after it has been encoded in Base64 format and disguised within a JPEG file.

Besides payment card data, the FBI said hackers are able to collect several pieces of personally identifiable information (PII). This includes customers’ names, physical addresses and telephone numbers.

One thing that may affect the scope of the threat is the fact that MAGMI only works with early versions of Magento. Some of these, such as Magento 1.x branch, are scheduled to reach end of life by next month. This means sites running that version won’t continue to receive security updates from the vendor.

End the Opportunity for E-Skimming via MAGMI

The FBI’s recommendations for mitigating the risk of the attacks include updating to more recent versions of Magento and making sure the systems are properly patched and up to date.

E-commerce store owners could also be in a better position to detect an attack by having a managed firewall service that can log potential problems and block unauthorized users.