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An Anonymous Coward writes:

OK, so you've air-gapped that PC. Cut the speakers. Covered the LEDs. Disconnected the monitor. Now, about the data-leaking power supply unit [theregister.co.uk]...

Video Israeli cyber-security side-channel expert Mordechai Guri has devised a way to pilfer data from devices that have been air-gapped and silenced.

[...]

An obvious defense against acoustic data transmission is to disable any speakers on the protected device, a practice known as audio-gapping.

But Guri's latest research shows that's not enough. He and his team have found a way to turn the power supply in an isolated, muted machine into a speaker of sorts, one capable of transmitting data at a rate of 50 bits/sec.

He calls the attack POWER-SUPPLaY. The technique has the potential to be used against PC workstations and servers, as well as embedded systems and IoT devices that have no addressable audio hardware.

"We show that malware running on a PC can exploit its power supply unit (PSU) and use it as an out-of-band speaker with limited capabilities," a paper [PDF] [arxiv.org] detailing the technique explained. "The malicious code intentionally manipulates the internal switching frequency of the power supply and hence controls the waveform generated from its capacitors and transformers."

[...]

Guri and others have developed a handful of similar TEMPEST attack schemes, such as luminance signaling via LCD screen fluctuations (BRIGHTNESS), acoustic signaling using fan modulation (FANSMITTER), data exfiltration via power cables (POWERHAMMER), and covert signaling via keyboard lights (CTRL-ALT-LED).

- archive.org alternate link [archive.org]

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