Visa warns of new sophisticated credit card skimmer dubbed Baka

Visa issued a warning regarding a new credit card JavaScript skimmer, tracked as Baka, that implements new features to evade detection.

Visa issued a warning regarding a new e-skimmer known as Baka that removes itself from memory after having exfiltrating payment card details.

The e-skimmer was first spotted by experts with Visa’s Payment Fraud Disruption (PFD) initiative in February 2020 while analyzing a command and control (C2) server employed in another campaign and that hosted an ImageID e-skimming kit.

Baka is a sophisticated e-skimmer developed by a skilled malware developer that implements a unique obfuscation method and loader.

“The most compelling components of this kit are the unique loader and obfuscation method. The skimmer loads dynamically to avoid static malware scanners and uses unique encryption parameters for each victim to obfuscate the malicious code.” reads the alert published by VISA. “PFD assesses that this skimmer variant avoids detection and analysis by removing itself from memory when it detects the possibility of dynamic analysis with Developer Tools or when data has been successfully exfiltrated.”

PFD experts found the Baka skimmer on several merchant websites across the world that are using Visa’s eTD capability.

The Baka loader works by dynamically adding a script tag to the current page that loads a remote JavaScript file. The JavaScript URL is hardcoded in the loader script in encrypted format, experts observed that the attackers can change the URL for each victim

The e-skimmer payload decrypts to JavaScript written to resemble code that would be used to render pages dynamically.

The final payload and the loader use the same encryption method, once executed, the software skimmer steals the payment card data from the checkout form.

Baka is also the first JavaScript skimming malware to use an XOR cipher to encrypt hard-coded values and obfuscate the skimming payload delivered by the command and control.

“While the use of an XOR cipher is not new, this is the first time Visa has observed its use in JavaScript skimming malware. The developer of this malware kit uses the same cipher function in the loader and the skimmer.” continues the alert.

The alert includes Indicators of Compromise and the following list of best practices and mitigation measures:

• Institute recurring checks in eCommerce environments for communications with the C2s.
• Ensure familiarity and vigilance with code integrated into eCommerce environments via service providers.
• Closely vet utilized Content Delivery Networks (CDN) and other third-party resources.
• Regularly scan and test eCommerce sites for vulnerabilities or malware. Hire a trusted professional or service provider with a reputation of security to secure the eCommerce environment. Ask questions and require a thorough report. Trust, but verify the steps taken by the company you hire.
• Regularly ensure shopping cart, other services, and all software are upgraded or patched to the latest versions to keep attackers out. Set up a Web Application Firewall to block suspicious and malicious requests from reaching the website. There are options that are free, simple to use, and practical for small merchants.
• Limit access to the administrative portal and accounts to those who need them.
• Require strong administrative passwords(use a password manager for best results) and enable two-factor authentication.
• Consider using a fully hosted checkout solution where customers enter their payment details on another webpage hosted by that checkout solution, separate from the merchant’s site. This is the most secure way to protect the merchant and their customers from eCommerce skimming malware.

Last year, Visa discovered another JavaScript web skimmer tracked as Pipka that was used by crooks to steal payment data from e-commerce merchant websites.

Pierluigi Paganini

(SecurityAffairs – hacking, Baka e-skimmer)