Writing Build script to setup our VM

Status

You can run vagrant status to check the status of your boxes

Let’s start this with vagrant up

Build script

Ok what is a build script?
Build script is used to setup the vulnerable VM
Like we can write set of commands in that file that need to setup the VM

Ex: update, upgrade, installing required tools, setting up the firewall, chaning hostname, changing permissions of files, creating/deleting users, changing passwords for the users

Ok let’s start

#!/bin/bash
echo "[+] Building our first vulnerable VM"
echo "[+] Getting update"
sudo apt-get update

First let’s do an update

echo "[+] Installing utilities"
apt install -y net-tools open-vm-tools

Now let’s install net tools and open vm tools (it’s mandatory)

echo "[+] Configuring hostname"
hostnamectl set-hostname pwn
cat <<EOF > /etc/hosts
127.0.0.1 localhost
127.0.0.1 pwn
EOF

Changing the hostname of the machine

echo "[+] Checking users || Creating users"
id -u pwn &>/dev/null || useradd -m pwn

Checking if there’s a user named pwn.

breakdown that command

vagrant@ubuntu-focal:~$ id -u pwn &>/dev/null
vagrant@ubuntu-focal:~$ echo $?
1

We can see the return value of a previous command by running echo $?
If the user exists then it’ll return 0, Now there’s no user named pwn
So the command next to || (or operator) will run useradd -m pwn

echo "[+] Symlinking history files to /dev/null"
ln -sf /dev/null /root/.bash_history
ln -sf /dev/null /home/pwn/.bash_history

After adding the user, Now we are symlinking bash history files to /dev/null

echo "[+] Setting passwords"
echo "root:1hop3Y0uN3veRf1nD7h1sPaSsW0rDDDD" | chpasswd
echo "pwn:w3lc0m379pWn&p41n" | chpasswd

Setting a strong password for user and root

echo "[+] Clean up"
rm -rf /root/.cache
rm -rf /home/pwn/.cache

Deleting the cache files
Don’t forget to delete your setup.sh (build script)
Coz it contains all information and passwords too
And delete other files your dropped in

Full script

#!/bin/bash
echo "[+] Building our first vulnerable VM"
echo "[+] Getting update"
sudo apt-get update

echo "[+] Installing utilities"
apt install -y net-tools open-vm-tools

echo "[+] Configuring hostname"
hostnamectl set-hostname pwn
cat <<EOF > /etc/hosts
127.0.0.1 localhost
127.0.0.1 pwn
EOF

echo "[+] Checking users || Creating users"
id -u pwn &>/dev/null || useradd -m pwn

echo "[+] Symlinking history files to /dev/null"
ln -sf /dev/null /root/.bash_history
ln -sf /dev/null /home/pwn/.bash_history

echo "[+] Setting passwords"
echo "root:1hop3Y0uN3veRf1nD7h1sPaSsW0rDDDD" | chpasswd
echo "pwn:w3lc0m379pWn&p41n" | chpasswd

echo "[+] Clean up"
rm -rf /root/.cache
rm -rf /home/pwn/.cache

Now we can run this script in our VM to setup it :D
So this is called a build script.
Let’s create our first vulnerable VM in next article :)