BadUSB reminded the world about the dangers of maliciously intelligent USB devices such as flash drives with modified firmware, but little has been released to effectively defend against the threat. A customizable man-in-the-middle USB connection can not only do that, but provide even more benefits to both attackers and defenders, such as modifying or denying specific traffic (similar to a USB write blocker) or bypassing mass storage restrictions in a locked-down corporate environment. In this talk, I will explain how to easily assemble a USB passthrough device using cheap, existing hardware and flash it to either attack secure environments, or isolate yourself from untrustworthy or potentially malicious peripherals. Instructions for purchasing the hardware, assembling it, and code for several different scenarios will be released and demonstrated.