UDP Command Listener

Introduction

The UDP Command Listener is a tool designed to receive and execute commands sent over a UDP connection on linux devices. It listens for incoming UDP packets on a specified port and processes the commands contained within those packets. This tool is particularly useful for remote command execution and automation tasks.

Configuration

The behavior of the UDP Command Listener can be configured using the ucl.conf configuration file. This file allows you to specify various settings, including the listening port and any authentication secrets.

Configuration File: ucl.conf

The configuration file looks like this:

#--------------------------------------------
# Configuration file for UDP Command Listener-
#--------------------------------------------

PORT=15000 # UDP listening port
SECRET= # Secret key to authorize command execution
....

It is important to set a strong secret key to prevent unauthorized access to the command execution functionality, but it is not required. You can leave it empty if you don't need authentication.

Whitelist and Blacklist

The UDP Command Listener has a whitelist and a blacklist for controlling which commands are allowed or denied. For obvious reasons, you can't have both of them functioning at the same time.

Whitelist

The whitelist is a list of commands that are explicitly allowed to be executed. If a command is not on the whitelist, it will be denied. It looks like this

whitelisted_commands_ON=true # Enable whitelisted commands
whitelisted_commands=( # Commands with spaces
    ls -lah
    shutdown -h now
) 

The program checks if every word in the command is in the whitelist before allowing execution. You need to introduce the complete command on the whitelist.

Blacklist

The blacklist is a list of commands that are explicitly denied from being executed. If a command is on the blacklist, it will be denied regardless of the whitelist settings. It looks like this

banned_commands_ON=true # Enable banned commands
banned_commands=( # Commands with spaces
    shutdown
    reboot
    sl
)

Usage

To use the UDP Command Listener, follow these steps:

1. Configure the ucl.conf file with the desired settings.
2. Start the listener by running the appropriate command (e.g., ./udp_command_listener, systemctl start udp_command_listener).
3. Send UDP packets to the specified port with the commands you want to execute on the device.

Installation

To install it, you need to run the installation script as root:

sudo ./install.sh

This will install the binaries to /usr/local/bin/udp_command_listener/ and the configuration to /etc/udp_command_listener/. It will also create the systemd service and a shortcut in /usr/bin/udp_receive.

Systemd Service

To start the service:

sudo systemctl start udp_command_listener.service

To enable the service at boot:

sudo systemctl enable udp_command_listener.service

To check the status:

sudo systemctl status udp_command_listener.service

Shortcut

You can run the listener manually from anywhere with:

udp_receive

Edit Configuration

To edit the configuration:

sudo udp_receive --config

This will open the /etc/udp_command_listener/ucl.conf file in the editor defined by the PREFERRED_EDITOR variable.

Examples of Use

NFC Automatization

You can use an NFC-enabled device to send commands to the UDP Command Listener. For example, you could configure your NFC tags to send specific commands when scanned, allowing for seamless automation of tasks. With an android device, you can use apps like Tasker or NFC Tools to create automations that trigger UDP packets to be sent to the listener.