Suppose I have a device that is a black box for me. It could be an IoT device that I would like to examine during a pen test. Suppose further that the device has a USB port. One thing I would like to know, is:
If I connect a USB device, say an HID device, is the corresponding driver loaded or not?
For keyboards, I thought it might work to play with Numlock. Since the Numlock LED is controlled by the driver, I could simply press Numlock to see what's going on (does it stay off, does it light up?). If nothing happens, the driver may not be loaded.
Is there a general approach to this? Is there a generic USB message indicating that the device can now be used?
The bottom line of my question is whether a device supports arbitrary USB devices or not, which could pose a security risk.