Juniper Threat Labs has been monitoring the activity of a botnet, which is now being referred to as ViroBot by TrendMicro in their blog, and would like to share additional information that can provide insight into the TTP (techniques, tactics, and procedure) of the threat actor. During our investigation, we also found a Unix keylogger related to this threat actor. The keylogger is a 64-bit ELF malware, and at the time of this writing, it has 0 hits on Virustotal. This blog shares technical aspects of both the Windows and Unix malware.
Virobot Ransomware Technical Analysis
We have acquired two samples of this malware, which are both .NET compiled samples:
The command arrives as a key-value pair with command strings, such as follows:
Results of the command are sent back to the server via the function UploadOrderResultAsync:
This command is the ransomware routine. First, it generates a random AES-256 key that will be used as the key for encrypting all files. This key is then encrypted using RSA, in which the public key is expected to be sent by the C2 server. It searches for all files in the %USERPROFILE% folder and encrypts the files with the following extensions.
After encryption, it add the extension “.enc” and displays the ransom note.
This command executes a binary from a download link supplied by the C2 server. The binary is saved in the %TEMP% folder with a random file name. The code had the option to run the sample in memory, but it was not implemented.
This command executes a string of command using the following:
This command retrieves a lot of information about the victim machine using WMI. It queries the following:
This command propagates via Outlook Mail as an attachment (most likely a version of itself or a downloader of itself). The attachment is downloaded from the same C2 server and then sends the mail to the Outlook contacts of the victim.
This command logs keystrokes and sends them back to the C2 server. The keylogged data is saved into a buffer in the memory and is sent back to C2 in NameValueCollection format.
During our investigation of the C2 server, we have identified an ELF binary that communicates to the same server. Upon analysis, we verified the sample to be a keylogger. As of the development of this blog, the sample has 0 VT detections.
This malware will execute itself as “/lib/systemd/systemd --user”
The keylogged data is saved into memory and sent back to the C2 server via HTTP POST.
It also has the capability to capture screenshots. The data is saved in base64 format and sent back to the server.
In this blog, we have provided technical details of a malware that has ransomware, bot and spreading capabilities. We have also identified a Linux keylogger attributed to the same threat actor that did not have Virustotal detections as of this writing. We believe that the malware is in its early stage of development as we have identified some unused functionalities and bugs in its code. This malware does not have the same capabilities compared to more mature malware developments, which have some form of obfuscation. Moreover, the C2 infrastructure is not robust as it is down as of this moment and we have not found a similar sample with a different C2. Despite this fact, combining multiple malware functionalities is something we should be wary of and we at Juniper will continuously monitor these type and threats.