CTF setup in Docker

This setup is intended to create a quick working environment to play Capture The Flags (CTF), HackTheBox and similar.

Setup

The easiest way to use this setup is to download docker-compose.yml and add the VPN config for the CTF; in this case, named ctf.ovpn. When those two are put in the same directory, run:

docker-compose up -d

Download

You could simply download the docker-compose.yml using:

curl https://raw.githubusercontent.com/arjentz/ctf-docker/main/docker-compose.yml > docker-compose.yml

Clone

Or you can clone the directory:

git clone https://github.com/arjentz/ctf-docker.git

To use the local containers, you need to change the following lines:

    image: arjenz/ctf-proxy

and:

    image: arjenz/ctf-kali

to:

    build: proxy

and:

    build: kali

respectively. Now you can edit the Dockerfiles and add packages as you please.

VPN credentials

In case credentials are required with the VPN config, create a file called credentials.txt with the username and password each on one line, uncomment the following line in docker-compose.yml:

      - ./credentials.txt:/vpn/credentials.txt:ro

And, if required, add the following line to the VPN config:

auth-user-pass /vpn/credentials.txt

Usage

You can use this setup in several ways.

Command line

When all containers are running, enter the Kali container using:

docker exec -it ctf-kali tmux -CC

From this shell any commands needed to play the CTF can be run.

Copy files

To copy a file to a volume, use:

docker cp $(pwd)/file.txt ctf-kali:/root/file.txt

Browser

Challenges might involve a webpage, that is what the proxy container is used for. Run your browser through the proxy (with or without extra proxies) to let the traffic go through the VPN.

X11 (on macOS)

To open an X11 application from inside the Kali container, first open XQuartz, and then run:

export DISPLAY=${hostname}:0 && xhost + ${hostname}

Now, it should be possible to open X11 applications. You can try it out with e.g. firefox or xtightvncviewer.

Use filesystem

If you want to use the filesystem instead of a Docker volume, change the line:

    - ctf_kali:/root

to:

    - ./data:/root

When you start the containers, this will create a folder ./data in which the root directory of your Kali container will be mounted. You can now simply copy files to this folder in order to use them in your container.

UID/GID (on Linux)

If using the filesystem on Linux, it is recommended to uncomment the following line in the docker-compose.yml:

    # user: '${UID}:${GID}'

And provide the environment variables when running the setup with:

UID=${UID} GID=${GID} docker-compose up -d

Customise

Feel free to edit anything in any way. Mount other config files, add containers, anything. Suggestions can also be added to this repository.

References

This setup makes use of dperson/openvpn-client and wernight/dante.