njRAT, also known as Bladabindi, is a remote access Trojan (RAT) that was first seen in 2013 and continues to be one of the most prevalent malware family. It was developed using the Microsoft .NET framework and, like many other RATs, provides complete control of the infected system and delivers an array of features to the remote attacker. There are multiple .NET obfuscation tools that make detection difficult for antivirus solutions and that hinder analysis by security researchers. njRAT utilizes dynamic DNS for command-and-control (C2) servers and communicates using a custom TCP protocol over a configurable port.

We covered njRAT builder kit in our previous blog published in 2015. In this blog, we will cover one of the newer variant of njRAT dubbed njRAT Lime Edition that we are seeing in the wild. This variant includes support for:

Ransomware infection
Bitcoin grabber
Keylogger
USB spreader
Password stealer
Bot killer
Screen Locker
DDoS (ARME,Slowloris)

Below is a snapshot of the njRAT Lime Edition configuration file:

Some highlights from the configuration files:

Configured to drop into Temp folder of the infected system with filename Client.exe
Bot Version: 0.7.3
C&C server: online2018.duckdns[.]org
Port Number: 1700

Upon receiving searchwallet command, the malware tries to gather the running process in the victim's machine and uses it to track crypto wallets when merchants buy or sell Bitcoins or make other payments. These digital wallets securely store digital currency, and they can be connected to bank accounts, debit cards, or credit cards, so that digital currency can be exchanged into and out of one's local currency.

Bitcoin core aka bitcoin-qt
Bitcoin.com
Electrum

The malware leverages windows WMI queries, such as "SELECT * FROM AntivirusProduct" and "SELECT * FROM Win32_VideoController," to check for VM or sandbox environment. It is capable of sending system information such as:

System Name
UserName
Windows Version
Bits(64 or 32 bit)
WebCam(Yes/No)
Active Window
CPU
Video Card
Memory
Volume Information
Installed Antivirus
Infection time

Malware monitors for the following process names on the victim machine and if found in running state, malware will try to kill the process:

Process Hacker
Process Explorer
SbieCtrl
SpyTheSpy
SpeedGear
Wireshark
Mbam
apateDNS
IPBlocker
Cports
KeyScrambler
TiGeR-Firewall
Tcpview
Xn5x
smsniff
exeinfoPE
Regshot
RogueKiller
NetSnifferCs
taskmgr
VGAuthService
VBoxService
Reflector
Capsa
NetworkMiner
AdvancedProcessController
ProcessLassoLauncher
ProcessLasso
SystemExplorer
ApateDNS
Malwarebytes Anti-Malware
TCPEye
SmartSniff
Active Ports
ProcessEye
MKN TaskExplorer
Currports
System Explorer
DiamondCS Port Explorer
Virustotal
Metascan Online
Speed Gear
The Wireshark Network Analyzer
Sandboxie Control
.NetReflector

This njRAT variant also has the capability of performing ARME and Slowloris DDoS attacks. Slowloris is an attack tool designed to allow a single machine to take down a server with minimal bandwidth, and also to send multiple partial HTTP requests. Slowloris tries to keep many connections to the target web server open and hold them open as long as possible. ARME attack also tries to exhaust the server memory.

The malware shuts down and restarts the system with the following command:

Switches:

-r -> restart the computer that's currently being used

-t -> time, in seconds

-f -> forces running programs to close without warning

We have seen the following C&C commands in the malware:

C&C Commands
delchrm	Delete chrome cookies and saved logins
MonitorOFF	Turn off monitor
TextToSpeech	Announces text received from C&C using TextToSpeech
NormalMouse	Restores normal mouse button functionality
taskmgrON	Enable task manager
ChngWLL	Change wallpaper
Kl	Keylogger command that checks foreground window and keys pressed
Seed	Sharing, downloading files with torrent software such as BitTorrent and uTorrent
ddos.slowloris.start	Start Slowloris attack
RwareSU	Drop and show ransom note
restartme	Restart the computer
DisableCMD	Disable command prompt
EventLogs	Delete event logs
BitcoinOFF	Stop Bitcoin monitor thread
Botk	Start the botkiller thread
pcspecs	Send system information (CPU/GPU/RAM)
Searchwallet	Check installed bitcoin wallets in the system and send to C&C server
PLG	Load plugin and configure with C&C server

The malware also has a WORM functionality to spread through USB that enumerates the files and folders on the hard drive. Once it detects the USB drive inserted into the system, it copies itself to the USB drive and creates a shortcut using the folder icon.

Ransomware functionality

The ransomware encrypts files with the extension .lime using the AES-256 symmetric algorithm, which means the key is the same for encryption and decryption.

Ransomware Key generation

When Lime is first launched, it will call a RandomString() function, which will attempt to generate an AES key. It generates a 50-byte array from the input string using a random index, and uses the random() function to fetch one character and stores it to the output string. Lime drops the output string at %AppData%\\Microsoft\\MMC\\hash location.