  This study investigates a primary inaudible attack vector on Amazon Alexa
voice services using near ultrasound trojans and focuses on characterizing the
attack surface and examining the practical implications of issuing inaudible
voice commands. The research maps each attack vector to a tactic or technique
from the MITRE ATT&CK matrix, covering enterprise, mobile, and Industrial
Control System (ICS) frameworks. The experiment involved generating and
surveying fifty near-ultrasonic audios to assess the attacks' effectiveness,
with unprocessed commands having a 100% success rate and processed ones
achieving a 58% overall success rate. This systematic approach stimulates
previously unaddressed attack surfaces, ensuring comprehensive detection and
attack design while pairing each ATT&CK Identifier with a tested defensive
method, providing attack and defense tactics for prompt-response options. The
main findings reveal that the attack method employs Single Upper Sideband
Amplitude Modulation (SUSBAM) to generate near-ultrasonic audio from audible
sources, transforming spoken commands into a frequency range beyond human-adult
hearing. By eliminating the lower sideband, the design achieves a 6 kHz minimum
from 16-22 kHz while remaining inaudible after transformation. The research
investigates the one-to-many attack surface where a single device
simultaneously triggers multiple actions or devices. Additionally, the study
demonstrates the reversibility or demodulation of the inaudible signal,
suggesting potential alerting methods and the possibility of embedding secret
messages like audio steganography.
