Lazarus Hacking Group is known for launching highly Sophisticated Cyber attacks targeting various sectors such as entertainment, financial services, defense, technology, and virtual currency industries, academia, and electric utilities.
Their activities including the development of various malware that was used for one of the biggest Wannacry Ransomware attacks in 2017, Sony cyber Attack on 2014 and Bangladesh Bank attack where attackers theft $81 million.
Once the server compromised they deploy previously unknown malware (Trojan.Fastcash) which intercepts the fraudulent withdrawal requests and send fake responses to dispense cash from ATMs.
ISO 8583 is standard message format that details the exchange between the credit/debit card issuers and the devices where it used such as point-of-sale devices and automated teller machines.
Attackers inject malicious codes into a legitimate process on application servers running the AIX operating system, the inserted malicious script has the ability to construct the ISO 8583 messages.
According to Symantec analysis, the malware monitors incoming messages and intercepts the attacker generated fraudulent transaction requests to prevent them from reaching the switch application.
Then it transmits a fake response approving fraudulent withdrawal requests and the hacker group drops cash from the ATM.
“Symantec has found several different variants of (Trojan.Fastcash), each of which uses different response logic. The attackers appear to have built in a capability to selectively deny transactions based on their own blacklist of account numbers.”