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https://github.com/jstrieb/ctf-collab

Collaborative programming environment inside GitHub Actions – like Google Docs for hacking
https://github.com/jstrieb/ctf-collab

collaboration ctf ctf-platform ctf-tools github-actions hack hacking hacking-tool hacking-tools ngrok tor tor-browser ttyd

Last synced: 11 days ago
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Collaborative programming environment inside GitHub Actions – like Google Docs for hacking

Awesome Lists containing this project

README 

        
# Introduction



Create an ephemeral, collaborative programming environment inside GitHub

Actions; conveniently save data with git. Particularly useful for solving

Capture The Flag

([CTF](https://en.wikipedia.org/wiki/Capture_the_flag#Computer_security))

problems.



Less technically: this is kind of like Google Docs for working on hacking

competitions collaboratively.



# Quick start



[Create a repo from the

template](https://github.com/jstrieb/ctf-collab-template/generate). Do the rest

of the steps from within your copy of the repository. The link to create a copy

of the repository will only work for users logged into GitHub.



In all cases, the username is `runner` and the password is `ctf`.



## Connect With Tor



Connecting over Tor is the most secure way to use the server, and doesn't

require signing up for any service. It does, however, require downloading the

Tor Browser Bundle. It also runs with noticeably higher latency than using the

alternative, non-Tor connection method.



0. [Create a repo from the

   template](https://github.com/jstrieb/ctf-collab-template/generate). Many of

   the following links will only work from within your copy of the repository.

   Creating a copy only works for users logged into GitHub.

1. Download and run the [Tor Browser

   Bundle](https://www.torproject.org/download/).

2. Navigate to the ["Run Collaborative CTF Environment"

   workflow](../../actions?query=workflow%3A"Run+Collaborative+CTF+Environment").

3. Start the server using the button in the top right ("Run workflow").

4. View the output; wait for it to print the connection information.

5. SSH in or connect from the Web using the connection information printed

   during the Action run. Note: whether connection to the `.onion` address

   using the browser or SSH, Tor Browser must be running.

6. Tor browser has a default setting that causes text to be illegible in `ttyd`

   and/or its dependency `xterm.js`. To fix this, go to `about:config` in the

   address bar, and set `privacy.resistFingerprinting` to `false`.



## Connect With ngrok (Without Tor)



Connecting over ngrok instead of Tor is a less secure, but lower-latency way to

connect to the server running on GitHub Actions. This method of connecting

doesn't require downloading Tor, but it does require signing up for ngrok.



0. [Create a repo from the

   template](https://github.com/jstrieb/ctf-collab-template/generate). Many of

   the following links will only work from within your copy of the repository.

   Creating a copy only works for users logged into GitHub.

1. [Sign up for ngrok](https://dashboard.ngrok.com/get-started/setup).

2. [Copy your ngrok

   Authtoken](https://dashboard.ngrok.com/auth/your-authtoken).

3. Navigate to the ["Run Collaborative CTF Environment"

   workflow](../../actions?query=workflow%3A"Run+Collaborative+CTF+Environment").

4. Paste in your ngrok Authtoken when you start the server using the button in

   the top right ("Run workflow").

   - To avoid pasting the Authtoken every time, paste it into a secret called

     `NGROK_TOKEN` under the [Secrets](../../settings/secrets/actions) settings

     area. It will be saved here and used automatically.

5. View the output; wait for it to print the connection information.

6. SSH in or connect from the Web using the connection information printed

   during the Action run.



## Once Connected



- By default, the collaborative environment uses `tmux` with Ctrl +

  A as the "prefix," and a few other custom keys that can be viewed

  in [.tmux.conf](dotfiles/.tmux.conf)

  - Read a [good introduction to

    `tmux`](https://www.hamvocke.com/blog/a-quick-and-easy-guide-to-tmux/)

  - Press Ctrl + A and then c to open a new

    window

  - Press Ctrl + A and then n to go to the

    next window and Ctrl + A and then p to go

    to the previous window

  - Press Ctrl + A and then | to split the

    current pane vertically (this is a vertical bar "|" – not the letter "L" or

    "i")

  - Press Ctrl + A and then S to split the

    current pane horizontally (this is a *capitalized* "S" – `tmux` cares about

    capitalization)

  - Press Ctrl + A and then one of the arrow keys to move

    to the pane in that direction

- By default, `tmux` adjusts the size of a window to accommodate the smallest

  viewer

  - Every window is the same size for all viewers, at all times

  - To make the window adjust to the largest client instead of the smallest,

    press Ctrl + A and then G (must be capital

    "G")

  - Be careful! This will mean that some of the window is difficult or

    impossible to see for the viewer with the smaller client

- Use the `quit` command to terminate the server for all connected users

  - Alternatively, the workflow can be canceled from within the GitHub web

    interface

- Create folders in the repo (`~/ctf`) for each CTF to stay organized

  - Save any changes by committing using `git` within the `~/ctf` folder

  - The default identity associated with commits is anonymous

- Theoretically, unlimited users can connect at once via Tor, and up to 40 can

  connect using ngrok for free

  - Practically, the real upper-limit is probably far lower

  - Every new user connects using the same link/connection information

  - Additional users do not need GitHub accounts to connect or commit to the

    repository from within the environment

  - Each user can create their own windows independently, or switch to windows

    created by other users

  - All connected users have passwordless `sudo` capabilities

- If you regularly install packages, add them to the [GitHub Actions

  workflow](./.github/workflows/run-server.yml#L35) so they are installed every

  time the environment starts up

  - The default packages that are installed in the environment can be viewed

    [here](./.github/workflows/run-server.yml#L35)



Graphical Server



**Don't use the graphical workflow unless absolutely necessary!**



0. [Create a repo from the

   template](https://github.com/jstrieb/ctf-collab-template/generate). Many of

   the following links will only work from within your copy of the repository.

   Creating a copy only works for users logged into GitHub.

1. [Sign up for ngrok](https://dashboard.ngrok.com/get-started/setup).

2. [Copy your ngrok

   Authtoken](https://dashboard.ngrok.com/auth/your-authtoken).

3. Navigate to the ["Run Graphical RDP CTF Environment (Ubuntu GNOME)"

   workflow](../../actions?query=workflow%3A"Run+Graphical+RDP+CTF+Environment+(Ubuntu+GNOME)").

4. Paste in your ngrok Authtoken when you start the server using the button in

   the top right ("Run workflow").

   - To avoid pasting the Authtoken every time, paste it into a secret called

     `NGROK_TOKEN` under the [Secrets](../../settings/secrets/actions) settings

     area. It will be saved here and used automatically.

5. View the output; wait for it to print the connection information.

6. Connect to the HTTP link in your browser or paste the connection link into

   your [remote desktop (RDP)

   client](https://en.wikipedia.org/wiki/Remote_Desktop_Protocol).

   - On Windows, press the start button and search for "Remote Desktop

     Connection" – the client should be installed by default.

   - On Linux [Remmina](https://remmina.org/how-to-install-remmina/) is a

     well-regarded RDP client.



# Who This Project is For



This project is for those with limited access to compute resources – students

in particular. By making it possible to connect from the web and over Tor, the

project is designed to be accessible to those who are behind a firewall and/or

are unable to install software on the computer they are using. For example,

someone who wants to participate in a CTF competition, but is using

shared computers in a library or a school computer lab.



## Be a Good Citizen



This project uses generously-offered, free resources in a way that was likely

not intended by GitHub. Please do not abuse them.



I claim no responsibility for how you use this project. Based on my reading of

GitHub's:



- [Terms of

  Service](https://docs.github.com/en/free-pro-team@latest/github/site-policy/github-terms-of-service#the-github-terms-of-service)

- [Acceptable Use

  Policy](https://docs.github.com/en/free-pro-team@latest/github/site-policy/github-acceptable-use-policies)

- and [Actions Usage

  Policy](https://docs.github.com/en/free-pro-team@latest/github/site-policy/github-additional-product-terms)



I have concluded that using this Actions workflow to do productive work,

particularly if you don't have the ability to run a Linux computer of your own,

is probably permissible if done in good faith, and with an effort made to

reduce excessive resource consumption. For example, don't use the graphical

workflows unless absolutely necessary, because they are considerably more

resource intensive to set up and run, and don't leave the workflows running

when not using them.



That being said, I may be reading the policies wrong, and GitHub has the right

to change them at any time. In particular, if this use of GitHub Actions is

abused, it is likely that future ability to do things like this will be limited

by GitHub. **If you like it, don't ruin it for others.**



Note: typical users get [3,000 minutes of private Actions

time](https://docs.github.com/en/free-pro-team@latest/actions/reference/usage-limits-billing-and-administration#usage-limits)

per month per user. This project can quickly run up that time if you are not

careful. Check your own usage [here](https://github.com/settings/billing) to

see how close to the limit you are. Also note that actions stop automatically

after 6 hours.



# Known Issues



- **Problem:** Tor browser loads the hidden service indefinitely, never

  connecting



  **Solution:** Restart Tor browser

- **Problem:** The web interface text is illegible when using Tor browser or

  Firefox



  **Solution:** Disable the `privacy.resistFingerprinting` setting in

  `about:config`

- **Problem:** The "Display connection info and sleep" workflow step fails when

  trying to display ngrok connection information



  **Solution:** The ngrok authtoken supplied either as input to the workflow,

  or as a repository secret is invalid or corrupted

- **Problem:** Connecting to the server using SSH over Tor fails



  **Solution:** Make sure Tor browser is running while the command is run. If

  it is still not working, try the command on port `9050` instead of `9150`

- **Problem:** Tor fails to bind to the port when running the workflow



  **Solution:** Run the action again. If it continues to fail, [open an

  issue](https://github.com/jstrieb/ctf-collab-template/issues/new)

- **Problem:** The web interface does not work with tor2web sites like

  [tor2web.io](https://tor2web.io) or [onion.sh](https://onion.sh)



  **Solution:** Use Tor browser and do not use tor2web sites



# How to Read This Code



- The vast majority of the code is contained in a single, [primary GitHub

  Actions workflow](./.github/workflows/run-server.yml), which sets up the

  environment and displays connection details to the user. This file is fairly

  well-commented, and most design decisions should have included justification.

  For readability, I have

  tried to use long command-line options where possible. There may be more

  information in the commit history, for example [this

  commit](https://github.com/jstrieb/ctf-collab-template/commit/47148f0ecc78c755cd69e5f09d76a4fc94530df9)

  justifies switching from [tmate.io](https://tmate.io) to ngrok and Tor.

- The [`dotfiles`](./dotfiles) directory contains configuration files for many

  programs running in the collaborative environment.

  - [`install.sh`](./dotfiles/install.sh) copies dotfiles to the proper

    locations

  - [`.tmux.conf`](./dotfiles/.tmux.conf) contains custom shortcuts for `tmux`

  - [`.bashrc`](./dotfiles/.bashrc) is pretty minimal, but contains a few

    useful command aliases

  - [`ttyd_run.sh`](./dotfiles/ttyd_run.sh) is run every time a new user

    connects via SSH or the Web interface and is responsible for opening a new

    `tmux` session that uses one common set of windows for all clients



# Acknowledgments



Thanks to my good friend Logan Snow ([@lsnow99](https://github.com/lsnow99))

for testing, fixing bugs, and other contributions!



This project makes use of several great software packages that have made their

services available for free:



- [Tor](https://www.torproject.org/)

- [ngrok](https://ngrok.com)

- [ttyd](https://github.com/tsl0922/ttyd)

- [tmux](https://en.wikipedia.org/wiki/Tmux)

- [GitHub Actions](https://github.com/features/actions)