ruroco is a tool that lets you execute commands on a server by sending UDP packets.
the tool consist of 3 binaries:
client
: runs on your notebook/computer and sends the UDP packetsserver
: receives the UDP packets and makes sure that they are validcommander
: 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.
- 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
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
ruroco-client gen --help
Generate a pair of private and public PEM keys
Usage: 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
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]
-s, --strict
Whether to enforce strict mode for source ip validation (defaults to true)
-i, --ip <IP>
Optional IP address from which the command was sent
-n, --ntp <NTP>
NTP server (defaults to using the system time) [default: system]
-4, --ipv4
Connect via IPv4 (defaults to true)
-h, --help
Print help
- run
ruroco-client gen
to generate two files:ruroco_private.pem
andruroco_public.pem
- move
ruroco_public.pem
to/etc/ruroco/ruroco_public.pem
on server - save
ruroco_private.pem
to~/.config/ruroco/ruroco_private.pem
on client - 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/server
and target/release/commander
See make goal install_client
. This builds the project and copies the client binary to /usr/local/bin/ruroco-client
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
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
- Download the
server-v<major>.<minor>.<patch>-x86_64-linux
andcommander-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
. - Make sure that the binaries have the minimal permission sets needed:
sudo chmod 500 /usr/local/bin/ruroco-server
sudo chmod 100 /usr/local/bin/ruroco-commander
sudo chown ruroco:ruroco /usr/local/bin/ruroco-server
- Create the
ruroco
user:sudo useradd --system ruroco --shell /bin/false
- Install the systemd service files from the
systemd
folder:sudo cp ./systemd/* /etc/systemd/system
- Create
/etc/ruroco/config.toml
and define your config and commands- Make sure that the configuration file has the minimal permission set needed:
sudo chmod 400 /etc/ruroco/config.toml
- Hint: If you edit the
[commands]
in/etc/ruroco/config.toml
then restart ruroco-commander
- Make sure that the configuration file has the minimal permission set needed:
- Since new systemd files have been added, reload the daemon:
sudo systemctl daemon-reload
- Enable the systemd services:
sudo systemctl enable ruroco.service
sudo systemctl enable ruroco-commander.service
sudo systemctl enable ruroco.socket
- Start the systemd services
sudo systemctl start ruroco-commander.service
sudo systemctl start ruroco.socket
sudo systemctl start ruroco.service
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:
# see chapter "server config"
[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 --strict false
:
ruroco-client send --address host.domain:8080 --command open_ssh --ip 94.111.111.111 --strict false
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 and set --strict true
(the default) - 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) --strict true
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.
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:
# see chapter "server config"
[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.
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 │
└────────────────┘ └────────────────┘
Whenever a user sends a command via the client, the following steps are executed
- 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
- server receives the UDP package (does not answer), decrypts it with the public key and validates its content
- if the content is valid, the server sends the command name to the commander. If the content is invalid an error message is logged
- 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 │
│ │ │ │ ├───────────────┐ │
│ │ │ │ │ │ │
│ │ │ │ │◄──────────────┘ │
│ │ │ │ │ │
└─────────┴────────────┴─────────┴─────────────────────────┴───────────────────┘