Security Experts:

Stealthy Crypto-Miner Has Worm-Like Spreading Mechanism

The PowerGhost crypto-miner is capable of remaining undetected on infected systems, and can spread on its own by leveraging a fileless infection technique, Kaspersky Lab has discovered.

The miner is targeting both workstations and servers, which allows it to spread across large corporate networks. The threat, Kaspersky discovered, leverages the National Security Agency-linked EternalBlue exploit to spread.

The new threat proves once again that the growing popularity and rates of cryptocurrencies have determined cyber-criminals to adopt ingenious mining techniques and to gradually drop ransomware Trojans as the malware of choice in favor of crypto-miners.

PowerGhost is an obfuscated PowerShell script containing not only the malware’s core code, but also a series of add-on modules such as the miner and libraries required for the miner’s operation, Mimikatz, a module for reflective PE injection, and a shellcode for the EternalBlue exploit.

By employing multiple fileless techniques, the malware remains inconspicuous to the user and undetected by antivirus technologies, Kaspersky notes.

During infection, which is performed via exploits or remote administration tools (Windows Management Instrumentation), a one-line PowerShell script is executed to drop the miner’s body and immediately launch it, without writing it to the hard drive.

After that, the script, which is PowerGhost itself, checks the command and control (C&C) server and, if a new version is available, it fetches and runs it.

Mimikatz is used to get the user account credentials from the machine. Then, the malware logs on and attempts propagation on the local network by launching a copy of the initial script via WMI. The threat also attempts to spread leveraging the EternalBlue exploit (CVE-2017-0144).

After using Mimikatz and WMI to spread to a new machine, the malware also attempts to escalate privileges on the newly infected system using various exploits (including one for CVE-2018-8120).

All modules are saved as properties of a WMI class, while the miner’s body is saved as a one-line PowerShell script in a WMI subscription that activates every 90 minutes. The miner is launched via reflective PE injection.

One PowerGhost version also included the ability to launch distributed denial of service (DDoS) attacks, likely because its authors attempted to make extra money by offering DDoS services.

This DDoS function is the only one that copies files to the hard drive and Kaspersky's security researchers believe it will be replaced with a fileless implementation in a future version of the malware. The researchers believe the DDoS function was added to the malware, because it is launched in a peculiar manner, where the DDoS module and a function to launch it are downloaded and saved to the disk separately.

To date, PowerGhost was mainly observed within corporate local area networks and has been mainly encountered in India, Brazil, Columbia, and Turkey.

Related: One Year After WannaCry Outbreak, EternalBlue Exploit Still a Threat

Related: Avoid Becoming a Crypto-Mining Bot: Where to Look for Mining Malware and How to Respond

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