My Kali Linux Setup for Playing HackTheBox

Fahmi J
6 min readJul 9, 2021
nobody@nothing

After using Kali 2019.4 for almost 2 years, I finally upgraded to version 2021.2 (fresh install). As a result, I had to reapply my settings and configurations on this newer version for playing HackTheBox (which I believe is applicable to other boot2root platforms as well). Therefore, I think it’s better to document my basic setup online. Hope it helps you as well.

Okay that’s enough for the intro, let’s set it up!

Display IP Address in the Shell Prompt

First, I would like to add an IP address in the shell prompt. Adding IP address in your prompt would be really helpful as it lets you copy the IP faster for reverse shell. To do so, we’ll need to modify the .zshrc file.

Before performing any modification, consider to make a backup of your original file using the following command:

$ cp ~/.zshrc{,.bak}

And then let’s create a custom section within the file using comments (I suggest placing it at the top).

# START CUSTOM 
...[custom script here]...
# END CUSTOM

Now add the following function to your .zshrc file.

function get_ip(){
# It can be thm or htb IP
tunnel_ip=`ifconfig tun0 2>/dev/null | grep netmask | awk '{print $2}'`
# Use eth0 as default IP,
default_ip=`ifconfig eth0 2>/dev/null | grep netmask | awk '{print $2}'`
if [[ $tunnel_ip == *"10."* ]]; then
echo $tunnel_ip
else
echo $default_ip
fi
}

The function assumes tun0 is the VPN interface to connect to HackTheBox network and eth0 is your default interface to connect to the Internet.

Then, find the following lines:

...
case "$PROMPT_ALTERNATIVE" in
twoline)
...

Under these lines, replace the entire PROMPT variable with the following line:

PROMPT=$'%F{%(#.blue.green)}┌──${debian_chroot:+($debian_chroot)─}${VIRTUAL_ENV:+($(basename $VIRTUAL_ENV))─}(%B%F{%(#.red.blue)}%n$prompt_symbol%m%b%F{%(#.blue.green)})-[%B%F{reset}%(6~.%-1~/.../%4~.%5~)%b%F{%(#.blue.green)}]-%B%F{152}[`get_ip`]%b%f%F{%(#.blue.green)}\n└─%B%(#.%F{red}#.%F{blue}$)%b%F{reset} '

Restart your terminal using one of the following commands.

$ zsh 
$ source ~/.zshrc

And we’re done with displaying IP address in the shell prompt.

OpenVPN Connection with Alias

It’s tiring when you have to type

$ sudo openvpn /path/to/config/file.ovpn

each time you want to connect to the VPN. So to make this easier we can leverage the alias command!

First let’s create a folder called .ovpnconfig in the home directory.

$ mkdir -p ~/.ovpnconfig

Then put all of your OpenVPN configuration files into that folder.

Finally, add some aliases into your .zshrc.

alias htbon='openvpn ~/ovpnconfig/htb-sg.ovpn 1>/dev/null &' 
alias htbfort='openvpn ~/ovpnconfig/htb-fortress.ovpn 1>/dev/null &'
alias htbrel='openvpn ~/ovpnconfig/htb-release.ovpn 1>/dev/null &'
alias kvpn='pkill openvpn'

Now we can type $ htbon or $ thmon in the command prompt to connect to the VPN.

Want to turn off the VPN? Simply type $ kvpn !

A Problem with Alias

In this Kali Linux version (non-root login), the only problem is that openvpn must be executed with sudo, because it needs administrative permission to create a network interface (that’s the tun0) .

Because of how alias works in Zsh:

Every eligible word in the shell input is checked to see if there is an alias defined for it. If so, it is replaced by the text of the alias if it is in command position (if it could be the first word of a simple command), or if the alias is global. If the replacement text ends with a space, the next word in the shell input is always eligible for purposes of alias expansion.

When you run $ sudo htbon, it will not expand the aliased command to $ sudo openvpn ~/ovpnconfig/htb-sg.ovpn 1>/dev/null &, instead it will return something like sudo: htbon: command not found.

Therefore, the solution to overcome this is by also aliasing the sudo command.

Add the following alias to your .zshrc file.

alias sudo='sudo '

Additionally, if you want to use sudo with no password for the default user kali, we can create a new sudoers file by running the following command.

$ sudo visudo /etc/sudoers.d/kali

Then add the following line to gives user kali sudo permission with no password.

kali  ALL=NOPASSWD: ALL

This time, we can run the alias command with sudo.

$ sudo <alias-command>
$ sudo htbon

Tools Transfer

Just like the OpenVPN files, I like to keep the essential tools to be centralized in one folder and so it can be hosted immediately.

Again, we can create a folder called tools.

$ mkdir -p ~/tools

Put your tools inside the folder. The following are some of the tools that I think to be essential (including web-shell).

Next, you can add another alias to host these tools immediately with one command. Feel free to create alias for yourself, mine called hostit.

alias hostit= 'python3 -m http.server -d ~/tools 8000'

Note Template

I’m using the following bash function which you can put in your .bashrc or.zshrc file to recreate my typical directory structure:

function mknote(){ 
mkdir nmap gobuster loot logs exploits ssh-keys post-exploits
}
  • nmap: each nmap scan goes here.
  • gobuster: each gobuster scan goes here.
  • loot: each interesting file for further analysis goes here.
  • logs: If you like to log your activity with $ script , put them here.
  • exploits: exploit script goes here.
  • ssh-keys: obtained ssh-key goes here, not loot.
  • post-exploits: post-compromise loot goes here.

Usage is simple:

$ cd htb-machine-folder/ 
$ mknote
$ tree
.
├── exploits
├── gobuster
├── logs
├── loot
├── nmap
├── post-exploits
└── ssh-keys

SSH Configuration

I have always use a separate SSH keys for CTF. My SSH key for CTF is using ed25519. You can create one using the following command:

$ ssh-keygen -a 100 -t ed25519 -f ~/.ssh/ctf_ssh

After that, register your private key to SSH agent.

$ eval "$(ssh-agent -s)" 
$ ssh-add ~/.ssh/ctf_ssh

Since HackTheBox machine starts with IP address of 10.10.*, add these lines to your SSH config (~/.ssh/config). Create one if you don't have it.

Host 10.10.* 
IdentityFile ~/.ssh/ctf_ssh

With the config above, whenever I injected my public key (/.ssh/ctf_ssh.pub) to HackTheBox machine for persistence access, I don’t have to specify -i /path/to/ssh/private/key anymore, but just with $ ssh machine-name@hostname.

QTerminal Configuration

Unfortunately I’m not a tmux user here. Tmux is rich in features, but I’m not comfortable with its prefix key. So far, I’ve always used the default QTerminal application and leveraged its shortcut feature to ’navigate’ a slightly faster in terminal.

If you’re a Windows Terminal user, you’ll familiar with some of these shortcuts:

  • ALT + Arrows: Move cursor between subterminals
  • CTRL + TAB: Navigate between tabs
  • CTRL + Arrow Left: Previous tab
  • CTRL + Arrow Right: Next tab
  • CTRL + N : New terminal tab
  • CTRL + SHIFT + W : Close current subterminal
  • CTRL + SHIFT + = : Split terminal vertically
  • CTRL + SHIFT + - : Split terminal horizontally
  • CTRL + SHIFT + F : Open search bar in terminal
  • CTRL + = : Zoom in
  • CTRL + - : Zoom out

The only limitation here is that there is no shortcut for resizing the sub-terminal.

Create OMZ Plugin

If you’re a Oh My Zsh user like me, by excluding SSH and QTerminal configurations, we can add these configuration into a custom plugin.

Save the following script to /home/<username>/.oh-my-zsh/custom/plugins/ctf/ctf.plugin.zsh.

The next step depends on your ZSH theme. I used a theme called robbyrussell.

I created a copy of the theme on /home/kali/.oh-my-zsh/custom/themes/robbyrussell.zsh-theme and modified the theme to display IP address and use two lines prompt. The modified version is as follows:

NEWLINE=$'\n$' 
PROMPT='%(?:%{$fg_bold[green]%}→:%{$fg_bold[red]%}→)'
PROMPT+=' %F{4}%n@%m %{$fg[cyan]%}«%c»%{$reset_color%}'
PROMPT+=' %B%F{152}«$(get_ip)»%f%b $(git_prompt_info)'
PROMPT+="%F{31}${NEWLINE} %f"
ZSH_THEME_GIT_PROMPT_PREFIX="%{$fg_bold[blue]%}git:(%{$fg[red]%}"
ZSH_THEME_GIT_PROMPT_SUFFIX="%{$reset_color%} "
ZSH_THEME_GIT_PROMPT_DIRTY="%{$fg[blue]%}) %{$fg[yellow]%}✗"
ZSH_THEME_GIT_PROMPT_CLEAN="%{$fg[blue]%})"

Finally, the plugin can be loaded in the .zshrc file.

...[SNIP]...
# Which plugins would you like to load?
# Standard plugins can be found in $ZSH/plugins/
# Custom plugins may be added to $ZSH_CUSTOM/plugins/
# Example format: plugins=(rails git textmate ruby lighthouse)
# Add wisely, as too many plugins slow down shell startup.
plugins=(git ctf)
...[SNIP]...

Restart your terminal and it’s done.

Okay, that’s all for this post!

Originally published at https://fahmifj.github.io on July 9, 2021. (Updated on 2023–07–14)

References

  • https://askubuntu.com/questions/750419/how-do-i-run-a-sudo-command-needing-password-input-in-the-background

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Fahmi J

Just curious to learn how things work, especially in digital world.