I was thinking along the same lines: a balun could harvest energy and use it for other purposes, but it should either store it for later use using maybe a tiny supercapacitor inside, or inject it into the data stream on the fly not unlike RFID dongles do. Or maybe just have enough power and memory to store a few hundred bytes and alter a few fields here and there, so that for example a network frame coming from a compromised machine can have its source field rewritten as it came from a trusted source. In theory small pull up resistors also could be swapped with lookalike malicious parts capable of tampering with i2c traffic between boards peripherals so that devices can be activated/deactivated no matter what the CPU tells them.
We're going straight to the point when there won't be a single device in the world, from toasters to supercomputers through top brand network gear, that can claim and guarantee to be secure; inserting malicious hardware and firmware is getting just too easy for those with the necessary knowledge and resources. A technically interesting and scary scenario.
The chips on Elemental servers were designed to be as inconspicuous as possible, according to one person who saw a detailed report prepared for Amazon by its third-party security contractor, as well as a second person who saw digital photos and X-ray images of the chips incorporated into a later report prepared by Amazon’s security team. Gray or off-white in color, they looked more like signal conditioning couplers, another common motherboard component, than microchips, and so they were unlikely to be detectable without specialized equipment.
Terrifying and neat; thanks for the explanation!
How easy is it for us (or rather the companies making the hardware) to detect and mitigate this?
it's not possible.
Technically you could embed and power an RF front-end inside a “flavored” balun to intercept or alter any communication passing through that front-end or even use the antenna to communicate during the down time. So this literally would hack Wifi / Bluetooth at low level and inject code and at the same time create a mesh network of malicious devices to relay information. Welcome to IoT Cyberwarfare.
But this clever hack is probably not limited to RF and is likely to also be embedded in transformers used for isolating Ethernet lines. Common mode chokes (some SMD chokes also look like the chip they are showing) or even some integrated ESD protection solution would be an ideal target as they are inserted in series of the signal.