Install and use of Docker

with Debian based Linux

Author: Stefan Waldvogel

Small machine with few cores: use Docker

-under construction, installation works but not accessing via external access-
Overview
This article shows a small introduction to Docker. I use Ubuntu, but you can follow this guide with Kali.

Docker? What is it?
Docker is a unique software (or container), and it simulates an entire operating system. You can use VMs to a different OS on your system, but Docker is more efficient and very fast. For a VM, you need dedicated hardware like a core and 4 GB RAM. Docker works differently, and it is not a problem to run 10 Docker containers on a single machine with 4 cores.

Usage
Let us say you do not have the financial support to buy a powerful machine, and cloud does not work either. You can do this: As the main system, you install a Kali Linux and run a Metasploitable2 in a Docker container. Now, you can sharpen your penetration testing skills.
Start with a guide like this: docs.rapid7.com/metasploit/metasploitable-2-exploitability-guide/, and you can learn penetration testing for free and everywhere.

Installation
The installation is simple. You can follow the official guide (docs.docker.com/engine/install/debian/) or follow these steps here.

Commands
sudo apt-get update
sudo apt-get install \
  apt-transport-https \
  ca-certificates \
  curl \
  gnupg \
  lsb-release

Add the key
sudo apt install curl

curl -fsSL https://download.docker.com/linux/debian/gpg | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg

echo \
"deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] https://download.docker.com/linux/debian \ $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

Install Docker
sudo apt-get install docker-ce docker-ce-cli containerd.io

Download centos
sudo docker pull centos
This is an example; you can download many different operating systems. You find them here: hub.docker.com/search?q=&type=image&category=os
This is the Docker hub. You see the matching command on the right side, and sometimes you can work with tags. Tags are used if you want to install a specific version. If we need an old Ubuntu 12.04 we can use the tag 12.04 to download it (sudo docker pull ubuntu:12.04)

Run or start a Docker container
sudo docker run -d -t --name mycentos centos

We want to see the running containers.
sudo docker ps -a

Now we can connect to the container
sudo docker exec -it mycentos bash

You can leave the container with
exit

Basic commands
docker ps -a {shows all existing Docker containers with their status}

Here, we see our mycentos, but we do not have a shell on this machine. The reason for this behavior is the -it switch. With this switch, we create an interactive shell, and if we exit the shell, the container is still in a state of "half" running.
If we test a container, we can use the command docker run -it-rm [IMAGE] to destroy the container after leaving it.

Start and stopping is simple
docker start [CONTAINER]
docker stop [CONTAINER]

You want to know what images you have
docker image ls

Connection to a running container
docker start mycentos
docker exec -it mycentos /bin/bash

With these commands, we can access the container.

Metasploitable 2 with Kali Linux

sudo docker pull tleemcjr/metasploitable2

sudo docker run -d -t --name mymet1 metasploitable2
sudo docker ps -a
sudo docker exec -it mymet2 sh -c "/bin/services.sh && bash"

Alternative in one command:
docker run --name mymet2 -it tleemcjr/metasploitable2:latest sh -c "/bin/services.sh && bash"

With Docker, you can do a lot more things but we will keep it simple.

On the right side, you see an IP address (172.17.0.3) and if you have Kali/Ubuntu on your main system you can run nmap against this machine.
Install nmap if not done:
sudo snap install nmap

we can run nmap with:
sudo nmap 172.17.0.3
and we will get an error (failed to open device docker0). The reason is, we have a network problem and the container is not reachable via our machine. Google can help us with a guide: blog.oddbit.com/post/2014-08-11-four-ways-to-connect-a-docker/

The oddbit guide requires a bit of Linux knowledge.
Create docker-pid with gedit
gedit docker-pid
-> copy the following commands and save the file.
#!/bin/sh
exec docker inspect --format '{{ .State.Pid }}' "$@"

Make it executable with
chmod +x docker-pid

Test the program with
sudo ./docker-pid {name of your running container}

We create a similar program for the IP address with the command
gedit docker-ip
#!/bin/sh
exec docker inspect --format '{{ .NetworkSettings.IPAddress }}' "$@"

chmod +x docker-ip
sudo ./docker-ip mymet4

Now, we have the ip and the pid of our container but we need to know out host IP, too. The command is:
ip a
In my network, there are a ton of other networks, but I want the IP for enp1s0

sudo ip addr add 172.17.0.12/21 dev enp1s0
sudo docker run -d --name mymet12 -p 172.117.0.12:100:80 tleemcjr/metasploitable2

sudo docker exec -it mymet12 sh -c "/bin/services.sh && bash"

sudo ip route add 172.17.0.10/16 dev docker0

sudo docker run -d --name mymet1 -p 192.168.1.20:90:80 tleemcjr/metasploitable2
sudo docker exec -it mymet1 sh -c "/bin/services.sh && bash"

docker run --name mymet2 -it -p 192.168.1.20:90:80 tleemcjr/metasploitable2:latest sh -c "/bin/services.sh && bash"

sudo apt-get install bridge-utils

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