Four passive attenuators in a 4 HP narrow module. Each one with an input, an output and an attenuating potentiometer in between. Nothing fancy here, no polarizing functions or such (not possible in a passive circuit by the way), but for around 20€ per attenuator you can't do anything wrong.
per attenuator: one input and one output
3U Eurorack module, 4 HP wide, 25 mm deep
passive module = no power consumption