COMfiltrat0r

COMfiltrat0r is a tool/technique developed by cyllective to bypass USB mass storage policies. You can read the full story and technical details in our blog post over at cyllective.com.

How does this work?

If policies still allow for serial devices, you can send data over serial (RS-232) to a microcontroller using a web browser that supports WebSerial.

Hardware Setup

Those steps should also be possible on different microcontrollers that support MicroPython.

Teensy 4.1

• Flash MicroPython onto your Teensy via the Teensy Loader
• Copy devices/teensy41/boot.py and devices/teensy/main.py onto a microSD card (cheap knockoff cards can cause errors)
• Plug the microSD card into the Teensy

Pico

• Flash MicroPython onto your Pico
  • Copy the uf2 file onto the file storage after connecting the Pico while holding BOOTSEL
• Wire up an SPI to microSD card interface

# You can use any SPI pins. Those are just the ones from the example code
CS   <-> Pin 17
SCK  <-> Pin 19
MOSI <-> Pin 20
MISO <-> Pin 16

• Plug in a microSD card (cheap knockoff cards can cause errors)
• Set up Thonny for the Pico and MicroPython
• Copy devices/pico/main.py and devices/pico/sdcard.py to the Pico via Thonny's file browser

Software Setup

You have multiple options:

• Visit cyllective.github.io/COMfiltrat0r via a supported browser
• Open index_combined.html in a supported browser

Known Problems

Depending on the client's operating system where the microcontroller gets plugged in, you may encounter that the device cannot be opened. This is the result of another program or even your OS taking control of the serial port.

Kudos

p5.webserial.js from gohai/p5.webserial