Visa issued a warning regarding a new JavaScript e-commerce skimmer known as Baka that will remove itself from memory after exfiltrating stolen data.
The credit card stealing script was discovered by researchers with Visa’s Payment Fraud Disruption (PFD) initiative in February 2020 while examining a command and control (C2) server that previously hosted an ImageID web skimming kit.
Last year, Visa discovered another JavaScript web skimmer known as Pipka that quickly spread to the online stores of “at least sixteen additional merchant websites” after being initially spotted on the e-commerce site of North American organizations in September 2019.
Evades detection and analysis
Besides the regular basic skimming features like configurable target form fields and data exfiltration using image requests, Baka features an advanced design indicating that it is the work of a skilled malware developer and it also comes with a unique obfuscation method and loader.
“The skimmer loads dynamically to avoid static malware scanners and uses unique encryption parameters for each victim to obfuscate the malicious code,” Visa’s alert reads.
“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.”
Baka was detected by Visa on multiple online stores from several countries and it was observed while being injected onto compromised e-commerce stores from the jquery-cycle[.]com, b-metric[.]com, apienclave[.]com, quicdn[.]com, apisquere[.]com, ordercheck[.]online, and pridecdn[.]com domains.
Camouflaged as page rendering code
The skimmer is being added to merchants’ checkout pages using a script tag and its loader will download the skimming code from the C2 server and execute it in memory.
This allows the attackers to make sure that the skimming code used to harvest the customers’ data isn’t found while analyzing files hosted on the merchant’s server or the customer’s computer.
“The skimming payload decrypts to JavaScript written to resemble code that would be used to render pages dynamically,” Visa explained.
“The same encryption method as seen with the loader is used for the payload. Once executed, the skimmer captures the payment data from the checkout form.”
Baka is also the first JavaScript skimming malware spotted by Visa to use an XOR cipher to obfuscate the skimming code downloaded from the C2 and any hard-coded values.
Best practices and mitigation measures
Visa recommends member financial institutions, e-commerce merchants, service providers, third-party vendors, integrator resellers to refer to its What to do if Compromised (WTDIC) document for guidance if their payment systems get compromised.
The company also shared the list of best practices for securing e-commerce platforms as outlined by the PCI Security Standards Council.
Additionally, Visa provides this list of mitigation actions that should prevent threat actors from compromising online stores to deploy JavaScript payment card skimming scripts:
• 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.