  A Negative Pressure Room (NPR) is an essential requirement by the Bio-Safety
Levels (BSLs) in biolabs or infectious-control hospitals to prevent deadly
pathogens from being leaked from the facility. An NPR maintains a negative
pressure inside with respect to the outside reference space so that microbes
are contained inside of an NPR. Nowadays, differential pressure sensors (DPSs)
are utilized by the Building Management Systems (BMSs) to control and monitor
the negative pressure in an NPR. This paper demonstrates a non-invasive and
stealthy attack on NPRs by spoofing a DPS at its resonant frequency. Our
contributions are: (1) We show that DPSs used in NPRs typically have resonant
frequencies in the audible range. (2) We use this finding to design malicious
music to create resonance in DPSs, resulting in an overshooting in the DPS's
normal pressure readings. (3) We show how the resonance in DPSs can fool the
BMSs so that the NPR turns its negative pressure to a positive one, causing a
potential \textit{leak} of deadly microbes from NPRs. We do experiments on 8
DPSs from 5 different manufacturers to evaluate their resonant frequencies
considering the sampling tube length and find resonance in 6 DPSs. We can
achieve a 2.5 Pa change in negative pressure from a $\sim$7 cm distance when a
sampling tube is not present and from a $\sim$2.5 cm distance for a 1 m
sampling tube length. We also introduce an interval-time variation approach for
an adversarial control over the negative pressure and show that the
\textit{forged} pressure can be varied within 12 - 33 Pa. Our attack is also
capable of attacking multiple NPRs simultaneously. Moreover, we demonstrate our
attack at a real-world NPR located in an anonymous bioresearch facility, which
is FDA approved and follows CDC guidelines. We also provide countermeasures to
prevent the attack.
