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USB Keystroke Injection Protection

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Overview

This tool is a daemon for blocking USB keystroke injection devices on Linux systems.

It supports two different modes of operation: monitoring and hardening. In monitor mode, information about a potentially attacking USB device is collected and logged to syslog. In hardening mode, the attacking USB device is ejected from the operating system by unbinding the driver.

Installation Prerequisites

The installation is mainly handled by setup.sh, however, there are some prerequisites that need to be adjusted before running the script:

  1. Install Python3.7 or later, python dev package, virtualenv (python3-venv) and PIP3 (python3-pip) if not already available on the system.

  2. Adjust the KEYSTROKE_WINDOW variable on top of the setup.sh file. This is the number of keystrokes the daemon looks at to determine whether its dealing with an attack or not. The lower the number, the higher the false positives will be (e.g., if the number is 2, the tool looks at only 1 interarrival time between those two keystrokes to determine whether it's an attack or not. Obviously, users sometimes hit two keys almost at the same time, which leads to the aforementioned false positive). Based on our internal observations, 5 is a value that is effective. However, it should be adjusted based on specific users' experiences and typing behaviour.

  3. Adjust the ABNORMAL_TYPING variable on top of the setup.sh file. This variable specifies what interarrival time (between two keystrokes) should be classified as malicious. The higher the number, the more false-positives will arise (normal typing speed will be classified as malicious), where more false-negatives will arise with a lower number (even very fast typing attacks will be classified as benign). That said, the preset 50000 after initial installation is a safe default but should be changed to a number reflecting the typing speed of the user using the tool.

  4. Set the mode the daemon should run in by adjusting the RUN_MODE variable on top of the setup.sh file. Setting it to MONITOR will send information about the USB device to a logging instance without blocking the device. Setting the variable to HARDENING will remove an attacking device from the system by unbinding the driver.

  5. Adjust the DEBIAN variable on top of the setup.sh file. This variable indicates whether the system the tool is installed on is a Debian derivate or something else. This determination is important for the installation of the systemd service later on (the path, the service will be copied to).

  6. Adjust the allowlist file in data/allowlist. This file will be installed to /etc/ukip/ on your system and taken as source of truth for allowed devices, in case a device is exceeding the preset ABNORMAL_TYPING speed. As described in the file, the allowed device can be narrowed down with a specific set of characters to allow to even more minimize the attack surface. For example, if your keyboard uses a macro that sends rm -rf / allow those characters, and even an attacking device spoofing your keyboards product ID and vendor ID couldn't inject an attack (except an attack using those specific characters obviously :D ). For other cases, the any keyword allows all possible characters for a specified device and none disallows all characters. Please keep in mind that this allowlist will only be taken into consideration, if a device is exceeding the set threshold.

  7. Adjust the keycodes file in data/keycodes. This file stores the relation between scancodes sent by the keyboard and keycodes you see on the keyboard. The default keycodes file as it is now has the scancode<->keycode layout for the US keyboard layout. If you are using a different layout, please adjust the file to fit your needs.

Installation

Once all of the above prerequisites are fulfilled, setup.sh should do the rest. It will install depending libraries into your users home directory ($HOME/.ukip/) so you don't have to install them system wide:

chmod +x setup.sh
./setup.sh

That's it: The daemon will be automatically started at boot time.

For interaction with the service, the systemd interface is probably the most convenient one. To check the status:

systemctl status ukip.service

To stop the service:

sudo systemctl stop ukip.service

Alternatively, to disable the service and prevent it from being started at boot time:

sudo systemctl disable ukip.service

Terms of use

USB Keystroke Injection Protection

This project provides code that can be run on Linux systems to harden those systems against keystroke injection attacks, delivered via USB. The terms of use apply to data provided by Google or implicitly through code in this repository.

This tool hereby grants you a perpetual, worldwide, non-exclusive,
no-charge, royalty-free, irrevocable copyright license to reproduce, prepare
derivative works of, publicly display, publicly perform, sublicense, and
distribute code in this repository related to this tool. Any copy you make for
such purposes is authorized provided that you reproduce this tool's copyright
designation and this license in any such copy.

Third-party Libraries

This project builds upon several open source libraries.
Please see each projects' Terms of use when using the provided code in this repository.

Disclaimer

This is not an officially supported Google product.