Now, fileless malware is going mainstream, as financially motivated criminal hackers mimic their nation-sponsored counterparts. According to research Kaspersky Lab plas to publish Wednesday, networks belonging to at least 140 banks and other enterprises have been infected by malware that relies on the same in-memory design to remain nearly invisible. Because infections are so hard to spot, the actual number is likely much higher. Another trait that makes the infections hard to detect is the use of legitimate and widely used system administrative and security tools—including PowerShell, Metasploit, and Mimikatz—to inject the malware into computer memory.
The researchers first discovered the malware late last year, when a bank's security team found a copy of Meterpreter—an in-memory component of Metasploit—residing inside the physical memory of a Microsoft domain controller. After conducting a forensic analysis, the researchers found that the Meterpreter code was downloaded and injected into memory using PowerShell commands. The infected machine also used Microsoft's NETSH networking tool to transport data to attacker-controlled servers. To obtain the administrative privileges necessary to do these things, the attackers also relied on Mimikatz. To reduce the evidence left in logs or hard drives, the attackers stashed the PowerShell commands into the Windows registry.