Researchers from UT San Antonio and UCCS present NUIT, the Near-Ultrasound Inaudible Trojan, which modulates voice commands into the 16-22 kHz band and lets the victim’s own speaker play them to the microphone from a website, app or video. Because voice assistants mute or turn down their speaker after the wake word, a device attacking its own microphone (NUIT-1) has to fit the command into a 0.77-second reaction window. A “turn the volume to 1” command keeps the assistant’s answer silent when a second device plays the attack (NUIT-2); on the same device only Siri plays along, since elsewhere it turns down the attack signal too. iPhones, MacBooks, Galaxy phones, an Echo Dot and Google Home all fell for it; only the iPhone 6 Plus resisted, thanks to the weak nonlinearity of its low-gain microphone amplifier. The Alexa part became CVE-2023-33248, which is a tricky one to patch when the vulnerable component is physics, although the authors sketch a defense that could ship as a software update.
