Trojan Either Encrypts Files or Mines for Cryptocurrency
7.7.18 securityweek Cryptocurrency

A long established ransomware family recently added the ability to deploy a cryptocurrency miner instead of file encryptor, based on the victim machine’s configuration.

The malware, which Kaspersky Lab detects as Rakhni, was first discovered in 2013 and has received numerous updates ever since. The latest feature added to the threat, however, makes it stand out from the crowd: the malware’s downloader checks the victim system and decides whether to infect it with a cryptor or a miner.

Mainly affecting users in Russia but spread worldwide, the Trojan is being distributed via spam emails with a malicious Word document attached. The file has an embedded PDF document that, once opened, launches a malicious downloader and also displays a fake error message to the victim.

The malware poses as software from Adobe, and even uses a fake digital signature featuring the name Adobe Systems Incorporated.

Once executed, it performs a series of checks to determine if it runs in a virtualized environment or if it is being analyzed, creates a registry key, and checks the process count, computer name, and IP address. The downloader also checks registry keys for specific strings associated with virtual machines, sandbox and analysis tools.

After completing this exhaustive list of checks (over 200), the threat proceeds to install a root certificate from its resources. The malware also checks for anti-virus programs on the system and can disable Windows Defender if no other AV process is found.

The downloader checks if the folder %AppData%\Bitcoin is present on the machine and drops the cryptor if it exists. If not, and there are more than two logical processors, the miner is dropped. If the folder doesn’t exist and there’s only one logical processor, the malware jumps to a worm component.

The cryptor performs its own set of checks on the machine, targets over 60 processes for termination, and only starts the encryption process if the system has been idle for 2 minutes. The malware targets nearly 200 file types for encryption, uses the RSA-1024 encryption algorithm, and appends the .neitrino to the affected files.

The miner generates a VBS script that gets launched after the system reboots, and which contains two commands to mine for Monero and Monero Original, respectively. Then, if the installation directory also contains the svchost.exe file, the malware launches it to mine for Dashcoin. A fake Microsoft certificate is used to hide the malicious process on the system.

“When this analysis was carried out, the downloader was receiving an archive with a miner that didn’t use the GPU. The attacker uses the console version of the MinerGate utility for mining,” Kaspersky explains.

The malware was also observed sending emails to a hardcoded address, to provide attackers with information such as computer name, IP address, malware’s path on the system, data and time, and malware build date, in addition to providing details on the infection itself.

The downloader was also observed attempting to spread to other computers on the local network. For that, it gets a list of network shares and then checks each computer to see if the folder Users is shared, in an attempt to copy itself to the Startup folder of each accessible user.

The malware also creates a batch file to delete all ‘temporary’ files used during infection, a rather common behavior.