North Korean hackers have advanced their cybercriminal activities by deploying a new Linux variant of the FASTCash malware, which targets the payment switch systems of financial institutions. This sophisticated malware is designed to facilitate unauthorized cash withdrawals from ATMs. Previously, FASTCash variants were known to target Windows and IBM AIX (Unix) systems, but the latest iteration specifically aims at Ubuntu 22.04 LTS distributions. The discovery of this variant has raised alarms within the cybersecurity community, as it represents an evolution in the tactics employed by state-backed hackers.
The Cybersecurity and Infrastructure Security Agency (CISA) first issued warnings about the FASTCash ATM cash-out scheme in December 2018, linking it to the North Korean hacking group known as “Hidden Cobra.” Investigations revealed that this group has been using FASTCash to execute coordinated ATM withdrawal attacks since at least 2016, resulting in losses of tens of millions of dollars across more than 30 countries. In 2020, the U.S. Cyber Command reiterated the threat, associating the renewed FASTCash activities with the advanced persistent threat group APT38, also known as Lazarus.
The newly identified Linux variant was first uploaded to VirusTotal in June 2023 and operates by injecting itself into running processes on payment switch servers through the ‘ptrace’ system call. This technique allows the malware to intercept and manipulate ISO8583 transaction messages, which are crucial for processing debit and credit card transactions. By targeting messages that indicate transaction declines due to insufficient funds, the malware cleverly replaces the “decline” responses with “approve” notifications, thereby authorizing fraudulent transactions without the knowledge of the bank or the cardholder.
Once the malicious message is successfully sent back to the bank’s central systems, it includes approval codes and an arbitrary amount of money, typically between 12,000 and 30,000 Turkish Lira (approximately $350 to $875). The bank, believing the transaction to be legitimate, approves it, allowing a money mule working for the hackers to withdraw cash from an ATM. As of now, the Linux variant has not been detected by standard security tools on VirusTotal, posing a significant risk to financial institutions. Moreover, a new Windows version of FASTCash was reported in September 2024, indicating that the threat actors are actively evolving their malware toolkit to exploit vulnerabilities in various operating systems.
