ruroco

ruroco is a tool that lets you execute commands on a server by sending UDP packets.

the tool consist of 4 binaries:

• client: runs on your notebook/computer and sends the UDP packets
• client-ui: presents all the functionality of client in an easier to use user interface.
• server: receives the UDP packets and makes sure that they are valid
• commander: runs the command encoded by the data of the UDP packet if it's valid

The commands are configured on the server side, so the client does not define what is going to be executed, it only picks from existing commands.

security

• client sends UDP packet to server, server never responds to it -> port-scanning does not help an adversary
• data sent from client to server is encrypted using RSA
• client only defines command to execute, commands are saved on server -> client can pick command but not define it
• run server software in such a way so that it uses as little operating system rights as possible
• replay protection by adding every packet that the server received to a blocklist
• (WIP) DoS protection

client ui usage

ruroco-client-ui

When first executed, a public-private key pair is generated and saved in the default config folder. The public key can then be copied from the user interface and saved on the server in the respective config.

client usage

commands

ruroco-client

Usage: client <COMMAND>

Commands:
  gen   
  send  
  help  Print this message or the help of the given subcommand(s)

Options:
  -h, --help     Print help
  -V, --version  Print version

gen

ruroco-client gen --help

Generate a pair of private and public PEM keys

Usage: ruroco-client gen [OPTIONS]

Options:
  -r, --private-pem-path <PRIVATE_PEM_PATH>
          Path to the private PEM file [default: ./ruroco_private.pem]
  -u, --public-pem-path <PUBLIC_PEM_PATH>
          Path to the public PEM file [default: ./ruroco_public.pem]
  -k, --key-size <KEY_SIZE>
          Key size for the PEM file [default: 8192]
  -h, --help
          Print help

send

ruroco-client send --help

Send a command to a specific address

Usage: client send [OPTIONS] --address <ADDRESS>

Options:
  -a, --address <ADDRESS>
          Address to send the command to
  -p, --private-pem-path <PRIVATE_PEM_PATH>
          Path to the private PEM file [default: ~/.config/ruroco/ruroco_private.pem]
  -c, --command <COMMAND>
          Command to send [default: default]
  -d, --deadline <DEADLINE>
          Deadline from now in seconds [default: 5]
  -e, --permissive
          Allow permissive IP validation - source IP does not have to match provided IP
  -i, --ip <IP>
          Optional IP address from which the command was sent. Use -6ei "dead:beef:dead:beef::/64" to allow you whole current IPv6 network. To do this automatically, use -6ei $(curl -s6 https://api64.ipify.org | awk -F: '{print $1":"$2":"$3":"$4"::/64"}')
  -n, --ntp <NTP>
          NTP server (defaults to using the system time) [default: system]
  -4, --ipv4
          Connect via IPv4
  -6, --ipv6
          Connect via IPv6
  -h, --help
          Print help

server config

1. run ruroco-client gen to generate two files: ruroco_private.pem and ruroco_public.pem
2. move ruroco_public.pem to /etc/ruroco/ruroco_public.pem on server
3. save ruroco_private.pem to ~/.config/ruroco/ruroco_private.pem on client
4. add server config to /etc/ruroco/config.toml -> see config.toml

download binaries from the releases page or build them yourself by running

make release

you can find the binaries in target/release/client, target/release/client_ui, target/release/server and target/release/commander

client

self-build

See make goal install_client. This builds the project and copies the client binary to /usr/local/bin/ruroco-client

pre-build

Download the client-v<major>.<minor>.<patch>-x86_64-linux binary from https://github.com/beac0n/ruroco/releases/latest and move it to /usr/local/bin/ruroco-client

server

self-build

See make goal install_server, which

• Builds the project
• Copies the binaries to /usr/local/bin/
• Adds a ruroco user if it does not exist yet
• Copies the systemd service files and config files to the right places
• Assigns correct file permissions to the systemd and config files
• Enables and starts the systemd services
• After running the make goal, you have to
  • generate an RSA key and copy it to the right place
  • setup the config.toml

pre-build

1. Download the server-v<major>.<minor>.<patch>-x86_64-linux and commander-v<major>.<minor>.<patch>-x86_64-linux binaries from https://github.com/beac0n/ruroco/releases/latest and move them to /usr/local/bin/ruroco-server and /usr/local/bin/ruroco-commander.
2. Make sure that the binaries have the minimal permission sets needed:
   1. sudo chmod 500 /usr/local/bin/ruroco-server
   2. sudo chmod 100 /usr/local/bin/ruroco-commander
   3. sudo chown ruroco:ruroco /usr/local/bin/ruroco-server
3. Create the ruroco user: sudo useradd --system ruroco --shell /bin/false
4. Install the systemd service files from the systemd folder: sudo cp ./systemd/* /etc/systemd/system
5. Create /etc/ruroco/config.toml and define your config and commands
   1. Make sure that the configuration file has the minimal permission set needed: sudo chmod 400 /etc/ruroco/config.toml
   2. Hint: If you edit the [commands] in /etc/ruroco/config.toml then restart ruroco-commander
6. Since new systemd files have been added, reload the daemon: sudo systemctl daemon-reload
7. Enable the systemd services:
   1. sudo systemctl enable ruroco.service
   2. sudo systemctl enable ruroco-commander.service
   3. sudo systemctl enable ruroco.socket
8. Start the systemd services
   1. sudo systemctl start ruroco-commander.service
   2. sudo systemctl start ruroco.socket
   3. sudo systemctl start ruroco.service

android

Building for android requires the following tools

• adb
• android sdk
• android ndk

For arch linux, the tools can be installed with the following commands. We use java 17, because that seem to be more stable than newer ones.

sudo pacman -S android-tools android-udev jdk17-openjdk
sudo archlinux-java set java-17-openjdk
yay -S android-ndk android-sdk android-sdk-build-tools android-sdk-platform-tools android-sdk-cmdline-tools-latest

You also have to install a platform. For arch linux, this can be done with the following commands. If sdk manager prints a java error, you might have to set your JAVA_HOME env var:

export JAVA_HOME=/usr/lib/jvm/default
sdkmanager --install "platforms;android-35"

you might have to set env vars:

export ANDROID_HOME=/opt/android-sdk
export NDK_HOME=/opt/android-ndk

export PATH=$PATH:$NDK_HOME/toolchains/llvm/prebuilt/linux-x86_64/bin
export PATH=$PATH:$ANDROID_HOME/tools
export PATH=$PATH:$ANDROID_HOME/platform-tools

Install xbuild (see https://github.com/rust-mobile/xbuild): cargo install xbuild and run x devices to check your devices connected with adb. Don't forget to put your android device in usb debugging mode.

Run the app on your device:

x run --device adb:<device-id>

single packet authorization (SPA)

If you host a server on the web, you know that you'll get lots of brute-force attacks on (at least) the SSH port of your server. While using good practices in securing your server will keep you safe from such attacks, these attacks are quite annoying (filling up logs) and even if you secured your server correctly, you will still not be 100% safe, see https://www.schneier.com/blog/archives/2024/04/xz-utils-backdoor.html or https://www.qualys.com/2024/07/01/cve-2024-6387/regresshion.txt

Completely blocking all traffic to all ports that do not have to be open at all times can reduce the attack surface. But blocking the SSH port completely will make SSH unusable for that server.

This is where ruroco comes in. Ruroco can execute a command that opens up the SSH port for just a short amount of time, so that you can ssh into your server. Afterward ruruco closes the SSH port again. To implement this use case with ruroco, you have to use a configuration similar to the one shown below:

[commands]
open_ssh = "ufw allow from $RUROCO_IP proto tcp to any port 22"         #  open ssh for IP where request came from
close_ssh = "ufw delete allow from $RUROCO_IP proto tcp to any port 22" # close ssh for IP where request came from

If you have configured ruroco on server like that and execute the following client side command

ruroco-client send --address host.domain:8080 --command open_ssh  

If you want to use a different IP address than the one you are sending the packet from, you can use the --ip argument together with --permissive:

ruroco-client send --address host.domain:8080 --command open_ssh --ip 94.111.111.111 --permissive

If you want to make sure that an adversary does not spoof your source IP address, you can get your external IP address from a service - the ruroco server will make sure that the IP addresses match:

ruroco-client send --address host.domain:8080 --command open_ssh --ip $(curl -s https://api64.ipify.org)

the server will validate that the client is authorized to execute that command by using public-key cryptography (RSA) and will then execute the command defined in the config above under "open_ssh". The --deadline argument means that the command has to be started on the server within 5 seconds after executing the command.

This gives you the ability to effectively only allow access to the SSH port, for only the IP that the UDP packet was sent from, if you want to connect to your server. Of course, you should also do all the other security hardening tasks you would do if the SSH port would be exposed to the internet.

You can define any number of commands you wish, by adding more commands to configuration file.

Enabling webservice

You may run a webservice like https://github.com/filebrowser/filebrowser on your server, which you do not want to publicly expose. If you use nginx as a reverse proxy, you can use ruroco to enable or disable services:

[commands]
disable_file_browser = "mv /etc/nginx/conf.d/https_file_browser.conf /etc/nginx/conf.d/https_file_browser.conf_disabled && nginx -s reload"
enable_file_browser = "mv /etc/nginx/conf.d/https_file_browser.conf_disabled /etc/nginx/conf.d/https_file_browser.conf && nginx -s reload"

If you have configured ruroco on server like that and execute the following client side command

ruroco-client send --address host.domain:8080 --command enable_file_browser

the file browser nginx config will be enabled and nginx reloaded, effectively making the file browser accessible.

overview

The service consists of three parts:

• client
  • binary that is executed on your local host
• server
  • service that runs on a remote host where you wish to execute the commands on
  • exposed to the internet
  • has minimal rights to receive and decrypt data and to communicate with the commander
• commander
  • daemon service that runs on the same host as the server
  • not exposed to the internet
  • has all the rights it needs to run the commands that are passed to it

┌────────────────┐ ┌────────────────┐
│                │ │                │
│   ┌────────┐   │ │ ┌────────────┐ │
│   │ Client ├───┼─┤►│   Server   │ │
│   └────────┘   │ │ └─────┬──────┘ │
│                │ │       │        │
│                │ │ ┌─────▼──────┐ │
│                │ │ │  Commander │ │
│                │ │ └────────────┘ │
│   Local Host   │ │   Remote Host  │
└────────────────┘ └────────────────┘

execution

Whenever a user sends a command via the client, the following steps are executed

1. client concatenates the current timestamp (in nanoseconds) with the command name (e.g. "default"), encrypts data with the private key and sends the encrypted data via UDP to the server
2. server receives the UDP package (does not answer), decrypts it with the public key and validates its content
3. if the content is valid, the server sends the command name to the commander. If the content is invalid an error message is logged
4. commander receives the command name and executes the command if the command is defined in the configuration

     ┌─────────┐            ┌─────────┐              ┌───────────┐              
     │ Client  │            │ Server  │              │ Commander │              
     └────┬────┘            └────┬────┘              └─────┬─────┘              
          │                      │                         │                    
          │ Encrypt and send     │                         │                    
          ├─────────────────────►│                         │                    
          │ data via UDP         │                         │                    
          │                      │ Decrypt and validate    │                    
          │                      ├─────────────┐ data      │                    
          │                      │             │           │                    
          │                      │◄────────────┘           │                    
          │                      │                         │                    
          │                      │                         │                    
          │                      │                         │                    
┌────┬────┼──────────────────────┼─────────────────────────┼───────────────────┐
│alt │    │                      │                         │                   │
├────┘    │                      │ Log error               │                   │
│if is    │                      ├─────────────┐           │                   │
│invalid  │                      │             │           │                   │
│         │                      │◄────────────┘           │                   │
│         │                      │                         │                   │
├─  ──  ──┤ ──  ──  ──  ──  ──  ─┤  ──  ──  ──  ──  ──  ── ├──  ──  ──  ──  ── │
│else     │                      │                         │                   │
│         │                      │ Send command name       │                   │
│         │                      ├────────────────────────►│                   │
│         │                      │                         │                   │
│         │                      │                         │ Check if command  │
│         │                      │                         │ is valid          │
│         │                      │                         ├───────────────┐   │
│         │                      │                         │               │   │
│         │                      │                         │◄──────────────┘   │
│         │                      │                         │                   │
│         │            ┌────┬────┼─────────────────────────┼───────────────────┤
│         │            │alt │    │                         │ Execute command   │
│         │            ├────┘    │                         ├───────────────┐   │
│         │            │if is    │                         │               │   │
│         │            │valid    │                         │◄──────────────┘   │
│         │            │         │                         │                   │
│         │            ├─  ──  ──┤ ──  ──  ──  ──  ──  ──  ├─  ──  ──  ──  ──  │
│         │            │else     │                         │Log Error          │
│         │            │         │                         ├───────────────┐   │
│         │            │         │                         │               │   │
│         │            │         │                         │◄──────────────┘   │
│         │            │         │                         │                   │
└─────────┴────────────┴─────────┴─────────────────────────┴───────────────────┘