Security News > 2021 > August > New Glowworm Attack Recovers Device's Sound from Its LED Power Indicator
Dubbed the "Glowworm attack," the findings were published by a group of academics from the Ben-Gurion University of the Negev earlier this week, describing the method as "An optical TEMPEST attack that can be used by eavesdroppers to recover sound by analysing optical measurements obtained via an electro-optical sensor directed at the power indicator LED of various devices."
While both methods retrieve sound from light via an electro-optical sensor, they are also different in that while the Lamphone attack "Is a side-channel attack that exploits a light bulb's miniscule vibrations, which are the result of sound waves hitting the bulb," Glowworm is a "TEMPEST attack that exploits the way that electrical circuits were designed. It can recover sound from devices like USB hub splitters that do not move in response to the acoustic information played by the speakers."
The attack hinges on the optical correlation between the sound that is played by connected speakers and the intensity of their power indicator LED, which are not only connected directly to the power line but also that the intensity of a device's power indicator LED is influenced by the power consumption.
In a real-world scenario, the threat model takes aim at the speech generated by participants in a virtual meeting platform such as Zoom, Google Meet, and Microsoft Teams, with the malicious party located in a room in an adjacent building, enabling the adversary to recover sound from the power indicator LED of the speakers.
In an indirect attack scenario where the power indicator LED isn't visible from outside the room, the eavesdropper can recover sound from the power indicator LED of the device used to provide the power to the speaker.
Although such attacks can be countered on the consumer side by placing a black tape over a device's power indicator LED, the researchers recommend device manufacturers to integrate a capacitor or an operational amplifier to eliminate the power consumption fluctuations that occur when the speakers produce sound.