  The popularity of ASR (automatic speech recognition) systems, like Google
Voice, Cortana, brings in security concerns, as demonstrated by recent attacks.
The impacts of such threats, however, are less clear, since they are either
less stealthy (producing noise-like voice commands) or requiring the physical
presence of an attack device (using ultrasound). In this paper, we demonstrate
that not only are more practical and surreptitious attacks feasible but they
can even be automatically constructed. Specifically, we find that the voice
commands can be stealthily embedded into songs, which, when played, can
effectively control the target system through ASR without being noticed. For
this purpose, we developed novel techniques that address a key technical
challenge: integrating the commands into a song in a way that can be
effectively recognized by ASR through the air, in the presence of background
noise, while not being detected by a human listener. Our research shows that
this can be done automatically against real world ASR applications. We also
demonstrate that such CommanderSongs can be spread through Internet (e.g.,
YouTube) and radio, potentially affecting millions of ASR users. We further
present a new mitigation technique that controls this threat.
