A Wolf in Sheeps Clothing Spreading Deadly Pathogens Under the Disguise of Popular Music_2

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A Wolf in Sheep’s Clothing: Spreading Deadly Pathogens Under

the Disguise of Popular Music

Anomadarshi Barua∗

University of California, Irvine

Irvine, CA, USA

anomadab@uci.edu

Yonatan Gizachew

Achamyeleh∗

University of California, Irvine

Irvine, CA, USA

yachamye@uci.edu

Mohammad Abdullah Al

Faruque

University of California, Irvine

Irvine, CA, USA

alfaruqu@uci.edu

ABSTRACT

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, dierential pressure sensors (DPSs) are utilized

by the Building Management Systems (BMSs) to control and mon-

itor the negative pressure in an NPR. This paper demonstrates a

non-invasive and stealthy attack on NPRs by spoong 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 nding to design malicious music to create

resonance in DPSs, resulting in an overshooting in the DPS’s nor-

mal 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 leak of deadly microbes from NPRs.

We do experiments on 8 DPSs from 5 dierent manufacturers to

evaluate their resonant frequencies considering the sampling tube

length and nd resonance in 6 DPSs. We can achieve a 2.5 Pa change

in negative pressure from a

∼

7 cm distance when a sampling tube

is not present and from a

∼

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

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 anony-

mous bioresearch facility, which is FDA approved and follows CDC

guidelines. We also provide countermeasures to prevent the attack.

CCS CONCEPTS

•Security and privacy →Embedded systems security

;Hard-

ware attacks and countermeasures.

KEYWORDS

Pressure sensors; Resonance; Negative pressure room; Pathogens

∗Both authors contributed equally to this research.

This work is licensed under a Creative Commons Attribution

International 4.0 License.

CCS ’22, November 7–11, 2022, Los Angeles, CA, USA

ACM ISBN 978-1-4503-9450-5/22/11.

https://doi.org/10.1145/3548606.3560643

ACM Reference Format:

Anomadarshi Barua, Yonatan Gizachew Achamyeleh, and Mohammad Ab-

dullah Al Faruque. 2022. A Wolf in Sheep’s Clothing: Spreading Deadly

Pathogens Under the Disguise of Popular Music . In Proceedings of the 2022

ACM SIGSAC Conference on Computer and Communications Security (CCS

’22), November 7–11, 2022, Los Angeles, CA, USA. ACM, New York, NY, USA,

16 pages. https://doi.org/10.1145/3548606.3560643

1 INTRODUCTION

A Bio-Safety Level (BSL) [

] is a set of strict regulations as-

signed to a biolab or hospital facility to prevent deadly pathogens

from being leaked from the facility. The BSL is ranked from BSL-1

(lowest safety level) to BSL-4 (highest safety level) depending on

the microbes that are being contained in a laboratory or hospital

setting. The Centers for Disease Control and Prevention (CDC) sets

BSLs to exhibit specic controls for the containment of microbes

to protect the surrounding environment and community.

BSLs require that the isolation rooms in a biolab or infectious-

control hospital maintain negative pressure with respect to the

outside hallway [

]. Therefore, the room is known as the Negative

Pressure Room (NPR). An NPR ensures that potentially harmful

microbes cannot leak from the facility through airow by main-

taining negative pressure inside. Therefore, an NPR is critical in

preventing deadly bioaerosols from escaping from the facility.

With rising concerns of bioterrorism, an NPR must maintain a

certain negative pressure following strict regulations established by

the CDC, ASHRAE, or other authorities [

]. The Dierential

Pressure Sensors (DPSs) are commonly used in NPRs to measure the

negative pressure in the facility [

]. The DPSs provide the pressure

data to the Heating, Ventilation, and Air Conditioning (HVAC)

systems, which maintains the negative pressure by controlling the

airow into NPRs [

]. In addition, a Room Pressure Monitoring

(RPM) system is also present in NPRs to monitor the room pressure

[

]. The RPM system also depends on the reading from the DPSs

installed in an NPR. Both RPM and HVAC systems are connected

with the Building Management Systems (BMSs) for automated

control and monitoring of the negative pressure in an NPR.

A DPS has an elastic diaphragm working as a pressure force

collector. Therefore, a DPS can be modeled as a second-order dy-

namic system with a resonant frequency [

]. We demonstrate by

thorough experiments that the resonant frequencies of DPSs used

in NPRS are typically in the audible range. In addition, we show

that the DPS with a sampling tube can be modeled as a Helmholtz

resonator, and the resonant frequency of a DPS with a sampling

tube still falls within the audible range. This nding is important

because an attacker, who has an intention to change the negative

arXiv:2210.03688v1 [cs.CR] 7 Oct 2022

CCS ’22, November 7–11, 2022, Los Angeles, CA, USA Anomadarshi Barua, Yonatan Gizachew Achamyeleh, & Mohammad Abdullah Al Faruque

pressure in an NPR, may use an audible sound having a resonant fre-

quency to create resonance in a DPS and generate a forged pressure

to perturb the normal readings of a DPS located in an NPR.

However, a sound having a single-tone resonant frequency will

create a "beep"-ish sound, which makes the attack easily identiable

by the authority. Moreover, the HVAC and RPM systems cannot be

fooled by a simple resonance in DPS because these systems have a

slower response time compared to a resonance. Therefore, a simple

resonance in DPS is not enough to turn NPR’s negative pressure

into a positive pressure to leak airborne pathogens from an NPR.

To solve the above problems, this paper adopts a smart strategy

by disguising the resonant frequency band inside popular music.

The resonant frequencies are inserted as a segment into the music

for a certain duration in every specic interval. Every inserted

segment of the resonant frequency is ended at its peak. Therefore,

the corresponding pressure wave inside a DPS also ends at its peak.

As a DPS with a sampling tube is a second-order oscillating system

[

], the pressure wave does not instantly fall to zero from the peak

value. Instead, the pressure wave starts to attenuate from its peak

exponentially. If the interval between two consecutive segments is

small, the pressure wave never falls below a certain value. Therefore,

a forged pressure is always present inside a DPS having an average

value greater than zero. As a result, the malicious music injected

into the DPS can fool the controller of HVAC and RPM systems

connected with BMSs to change the negative pressure of an NPR

into a positive one. Moreover, the segments of resonant frequency

are camouaged in the malicious music so that the attack is not

identiable by the authority. Therefore, we name this attack as "the

wolf in sheep’s clothing" since this strategy ensures stealthiness.

The consequences of changing a negative pressure into a positive

one can be catastrophic. If the NPR has an infectious patient admit-

ted or an ongoing bioresearch, the attacker can control the timing

of the attack to leak a deadly pathogen from the NPR. Moreover,

an abnormal change in NPR’s pressure triggers an alarm that may

create chaos in the facility. An attacker can use this chaos to initiate

a stronger attack, such as stealing deadly microbes from the NPR

or physically attacking the biosafety cabinets in an NPR. Therefore,

our attack model is strong and impactful and has the potential to

cause tremendous losses in human lives and monetary resources.

Contributions:

We have the following technical contributions:

(1)

We evaluate eight industry-used pressure sensors from ve

dierent manufacturers to show that the pressure sensors used in

NPRs have resonant frequencies in the audible range.

(2)

We design malicious music disguising the resonant frequen-

cies of DPSs inside of the music to fool the HVAC and RPM systems

of an NPR. We show through experiments that this strategy can

change the negative pressure of an NPR to a positive one.

(3)

We show that the attacker can adversarially control the forged

pressure in DPSs by using the malicious music. Moreover, we show

that the attacker can also simultaneously attack multiple NPRs in a

facility using our attack model.

(4)

We demonstrate our attack model at a real-world NPR located

in an anonymous bioresearch facility. The NPR is approved by the

Food and Drug Administration (FDA) and follows CDC guidelines.

We also provide countermeasures to prevent the attack on NPRs.

Demonstration:

The demonstration of the attack is shown in

the following link: https://sites.google.com/view/awolnsheepsclot

hing/home

2 BACKGROUND

2.1 NPR and its importance

An NPR [

] maintains lower pressure inside with respect to the

outside reference space. As air typically travels from higher pressure

areas to lower pressure areas, NPR ensures that clean air is drawn

into the room so that contaminated particles inside the room are

not able to escape. This is why NPRs are present in hospitals and

biosafety labs as they prevent airborne particles like bacteria and

viruses from spreading out from the facility. NPRs are also present

in safety-critical facilities, such as pharmacies and clean rooms.

Importance

: The safety of NPRs is paramount as spreading air-

borne microbes from NPRs may result in catastrophic consequences.

For example, a deadly fungus belonging to the genus Aspergillus is

an airborne pathogen that can cause Aspergillosis disease resulting

in acute pneumonia and abscesses of the lungs and kidneys [

]. It

has a mortality rate of

∼

100% for people with neutropenia (i.e., low

neutrophils). Respiratory tract infections, such as inuenza, swine

u, and COVID-19, are great examples of airborne pathogens that

result in a worldwide pandemic. Recently, a conspiracy theory has

been rumored about the leakage of the COVID-19 as bioweapons

from a biolab [

]. In this context, imagine an attacker with the

intention of spreading infectious disease as bioweapons may target

NPRs, where either infected patients are admitted for isolation or

research is carried out on deadly pathogens. Therefore, the security

of NPRs is critical and is regulated with strict guidelines.

2.2 Regulations for NPRs

With rising concerns about bioterrorism and emerging infectious

diseases, there has been a greater emphasis on the proper regu-

lations of NPRs. NPRs must follow requirements established by

the CDC [

], ASHRAE [

], and healthcare design construction

guidelines [

] to correctly manage airborne infections. Dierent

authorities follow their own regulations [

] to maintain a

certain negative pressure in NPRs (see Table 1). For example, CDC

requires that NPRs must maintain a negative pressure dierential

of at least

∼

2.5 Pa (i.e., 0.01 inch water column) in a hospital or

biolabs and change the air at least 12 times per hour [

]. Moreover,

exhaust from NPRs must be allowed to exit directly outside without

contaminating exhaust from other locations. In addition, all exhaust

air must be discharged through a High-Eciency Particulate Air

(HEPA) lter to prevent any contamination in the environment.

Table 1: Regulations for a Negative Pressure Room (NPR).

Country Taiwan CDC(USA) AIA(USA) Australia

Negative pressure -8 Pa -2.5 Pa -2.5 Pa -15 Pa

Air change per hour (ACH)

8 -12 > 12 > 12 > 12

2.3 Types of pressure sensors used in NPRs

Traditionally, hot-wire anemometers [

] and ball pressure sensors

[

] were used to measure pressure in NPRs. However, they have

limitations, such as they are highly sensitive to dust, require pe-

riodic maintenance, and cannot be connected to a BMS or RPM

for real-time control. Therefore, transducer-based pressure sensors

A Wolf in Sheep’s Clothing: Spreading Deadly Pathogens Under the Disguise of Popular Music CCS ’22, November 7–11, 2022, Los Angeles, CA, USA

(TBPSs) are replacing hot-wire and ball pressure sensors in NPRs

since TBPSs are more accurate, reliable, require low maintenance,

and can be connected to BMS or RPM for real-time monitoring.

Physics of TBPSs:

A force collector and a transducer are two

fundamental components of TBPSs. A force collector, such as an

elastic diaphragm, is combined with a transducer to generate an

electrical signal [39] proportional to the input pressure.

Types of TBPSs:

In general, TBPSs work in one of three modes:

absolute, gauge, or dierential measurement. Absolute pressure

sensors use vacuum pressure, and gauge sensors use local atmo-

spheric pressure as the static reference pressure. On the other hand,

Dierential Pressure Sensors (DPSs)

measure the dierence be-

tween any two pressure levels using two input ports (see Fig. 1).

Therefore, DPSs are naturally suitable in such applications where

the pressure dierence is required to be measured, such as in NPRs

[

]. As a DPS has high sensitivity to dierential pressure and is

deployed in NPRs, we focus on DPSs in next sections.

Transducer

(capacitor

plates)

Elastic

diaphragm

Output

voltage

Input port P2

Input port P1

Input port P2

Input port P1

A physical DPS

Figure 1: Basics of a DPS having two input ports.

2.4 Types of dierential pressure sensors

DPSs typically have a elastic diaphragm placed in between two

pressure input ports

𝑃1

and

𝑃2

(see Fig. 1). The diaphragm senses the

dierential pressure

𝑃1

𝑃2

applied to the pressure input ports by

changing its shape. The diaphragm’s shape change is converted to a

proportional output voltage by using a transducer. DPSs either use

acapacitor, or a piezoresistor, or thermal mass-ow as a transducer.

A DPS is named after the type of transducer it has.

Fig. 1 shows a capacitive DPS as an example. The diaphragm

is placed in between rigid capacitor plates. A dierential pressure

applied to the diaphragm generates a proportional change in the

capacitive transducer resulting in a proportional voltage at the

sensor output. We refer to Appendix 13.1 for details on other types.

2.5 Dierential pressure sensors used in NPRs

DPSs are highly sensitive to a small dierential change in the low

pressure range (i.e., Pa range) and are naturally suitable to measure

a pressure dierence. Therefore, DPSs are a natural choice to be

used in most RPM/BMS systems to control the negative pressure. To

prove the prevalence of DPSs in NPRs, we investigate six industry-

used RPM systems designed by popular manufacturers. All of these

RPM systems use dierent types of DPSs that are shown in Table 2.

Table 2: Dierential pressure sensors used in NPRs

Sl. RPM/DPS part# Type Technology Manufacturer

1 Series RSME [12] Capacitive Dierential Dwyer

2 SRPM 0R1WB [7] Capacitive Dierential Setra

3 One Vue Sense [8] Unknown Dierential Primex

4 RSME-B-003 [10]

Piezoresistive

Dierential Dwyer

5 Siemens 547-101A [9] Unknown Dierential Siemens

6 Series A1 [11]

Piezoresistive

Dierential Sensocon

7 GUARDIAN [21] Unknown Dierential Paragon Con.

2.6 Resonant frequency of a DPS and resonance

Resonant frequency:

As mentioned in Section 2.3 and 2.4, typ-

ically, DPSs have a diaphragm/membrane and a transducer. There-

fore, the pressure transducer system in DPS is considered as a

second-order dynamic system, analogous to a bouncing ball [

Hence, the transducer system in a DPS has its own resonant fre-

quency,

𝑓𝑟

, which depends on the mass and stiness of the di-

aphragm and mass of the pressure medium as Eqn. 1 [35].

𝑓𝑟=

2𝜋stiness of a diaphragm

mass of the pressure medium and diaphragm (1)

Resonance:

Resonance occurs when the frequency of the input

pressure wave matches the resonant frequency of the driven trans-

ducer system in a DPS, resulting in oscillations [

] in the trans-

ducer at large amplitude. This results in signicant error by over-

shooting the peaks and troughs in the actual pressure wave, with

an overestimation/underestimation of the actual reading. There-

fore, users ensure that a DPS typically operates below its resonant

frequency to prevent the resonance. A thumb’s rule is 20% of the

resonant frequency is typically used as the usable frequency limit

for a given DPS [24]. This concept is illustrated in Fig. 2.

20% of fr

DPS is operated in 20%

of fr to avoid resonance

Frequency in log scale (Hz)

Magnitude (db)

Figure 2: Resonant frequency in a DPS.

2.7 Electronics inside of a DPS

DPSs have a signal conditioning block in addition to a transducer

(see Fig. 3). The signal conditioning block has dierential ampliers,

low-pass lters (LPFs), and analog-to-digital converters (ADCs).

A dierential amplier amplies the output after removing the

common-mode noises. An LPF with an ADC digitizes the measured

value. Both analog and digital DPSs are available on the market.

Analog DPSs output the analog signals from the dierential ampli-

er directly, while digital DPSs contain the LPF and ADC.

Transducer

Elastic

diaphragm

Output

voltage

Input port P2

Input port P1

Amplifier

LPF

ADC

Digital DPS

Figure 3: Dierent components inside of a DPS.

3 BASICS OF AN NPR

This section explains the construction of an NPR, where and how

the DPSs are deployed in an NPR, and how the output from the

DPS controls the NPR’s control system.

3.1 Components of a real-world NPR

The components of an NPR vary depending upon the requirements

of dierent facilities. However, the core components are more or

less the same for most NPRs. Here, we detail the components of an

anonymous NPR where we have visited and experimented with to

CCS ’22, November 7–11, 2022, Los Angeles, CA, USA Anomadarshi Barua, Yonatan Gizachew Achamyeleh, & Mohammad Abdullah Al Faruque

validate our attack model.

Please note that the target NPR eval-

uated in this paper is located in a clean room in an anony-

mous bioresearch facility. This NPR is also approved by the

FDA and follows CDC guidelines.

A typical construction of an NPR is shown in Fig. 4. An NPR has

an HVAC system, which includes fresh air inlet ports. The fresh air

from the outside is treated with multistage lters and then supplied

to the isolation chamber of an NPR, including the anteroom, through

an air conditioning (AC) unit. The AC has a Variable Air Volume

(VAV) controller, which can increase or decrease the supply fan

speed, controlling the fresh airow to the NPR. An exhaust fan

continuously moves the contaminated air out from the NPR through

a HEPA lter using an exhaust pipe. The polluted air is further

treated with a post-ltration unit having an Ultraviolet (UV) lamp.

The room is maintained as airtight as possible. An RPM system is

installed at the wall and integrated with the BMSs.

PRE filter

Medium filter

Cooling coil

Heat pipe

PRE filter

Medium filter

Cooling coil

Heat pipe

Supply fan

UV light Cooling coil

Heat pipe

PRE filter

Medium filter

HEPA filter

UV light

Exhaust fan

Exhaust

air

HEPA filter

Anteroom Isolation chamber

Low pressure

port

High pressure

port

Sampling

tube

Hallway

DPSs are inside

of RPM/BMS

controller

RPM or BMS

controller

Filters, cooling coil

and heat pipes

Supply fan

Filters, cooling coil

and heat pipes

Fresh

air

Air conditioning

(AC) unit

HEPA, UV lamp,

post filter

Exhaust fan

Deadly microbes

contained inside

of NPR Exhaust air

Return air

Supply fan

DPS to check

filter clog

Fresh air

Pressure

pickup

device

Figure 4: Dierent components of a real-world NPR.

3.2 How DPSs are deployed in an NPR

The HVAC system ensures a negative pressure in the NPR by con-

trolling the fresh air and exhaust airow using the supply and

exhaust fan. An RPM system continuously monitors the negative

room pressure. The RPM and HVAC systems use DPSs to monitor

and control negative pressure in an NPR. The DPS is typically lo-

cated inside of RPM or BMS controller. Commonly, the input ports

of a DPS are connected with pressure ports using sampling tubes

(see Fig. 4 and 5). The pressure port located inside an NPR is known

as a low pressure port. The pressure port located outside an NPR

in a hallway/reference space is known as a high pressure port. The

sampling tube is connected with a pressure pickup device in the

pressure ports. The pressure pick-up device increases the surface

area of the sampling tube to pick up the target pressure accurately.

The low and high pressure ports are exposed and typically in-

stalled in eyesight near the door wall or on the ceiling of an NPR.

There are other DPSs used in the HVAC system to indicate whether

the lters of the HVAC are clogged or not. Typically they are not

installed in the eyesight. Therefore, they are not accessible.

Input ports

Low pressure

port

High pressure

port

Sampling

tube

Pressure

pickup device In NPR

In reference

space

DPS

Sampling

tube Input ports

DPS

High

pressure port

Pressure

pickup device

Low pressure

port

Figure 5: Pressure ports and sampling tube of a DPS.

3.3 Pressure control algorithm in an NPR

A pressure control algorithm running on the BMS controls the

HVAC system of the NPR to maintain a constant negative pressure.

A simplied control algorithm 1 is provided below. Algorithm 1

shows that the pressure readings from DPSs are used to control

the speed of the supply fan and exhaust fan when the negative

pressure increases or decreases from a reference value in the NPR,

maintaining the negative pressure close to the reference value. The

rest of the control algorithm 1 is self-explanatory.

Algorithm 1: Pressure control algorithm in an NPR.

Input: Pressure measurement data from DPSs

Output: Send control signals to the HVAC system

1for 𝑡←1to ∞do

2Track dierential pressure reading from DPS’s pressure ports

3if Negative dierential pressure increases from a reference value then

4Reduce the supply fan speed of the AC to control the fresh airow

5Increase the exhaust fan speed to increase the exhaust airow

6else if

Negative dierential pressure decreases from a reference value

then

Increase the supply fan speed of the AC to control the fresh airow

8Reduce the exhaust fan speed to reduce the exhaust airow

9else

10 Maintain the same state of the controller

4 ATTACK MODEL

Fig. 7 shows the dierent components of our attack model associ-

ated with NPRs. We discuss the components of the attack model

below in a point-by-point fashion.

Attacker’s intent:

The attacker creates a forged resonance in

the DPSs used in NPRs with malicious music having a frequency

equal to the resonant frequency of the DPSs. As a result. the over-

shooting occurs in the actual pressure reading, resulting in a change

in the negative pressure maintained in NPRs by the BMSs.

Target system:

The attacker targets a facility where NPRs are

used to contain deadly microbes and infectious airborne particles.

Such facilities include isolation rooms, clean rooms and pharmacies

in infectious-control hospitals, and biolabs in bioresearch facilities.

CCTV location

Low pressure port of a DPS is in eyesight

CCTV location

High pressure ports of a DPS are in eyesight

Inside of an NPR Outside of an NPR (Hallway)

The attacker

Figure 6: Pressure ports of DPSs are in eyesight in NPRs.

Attacker’s capabilities:

The attacker can surreptitiously place

an attack tool near the target pressure ports of a DPS used in an NPR.

The attack tool has an audio source. The audio source plays mali-

cious music having a frequency equal to the resonant frequency of a

DPS mounted in a target NPR. The audio source can be a simple cell-

phone or a speaker from an entertainment unit, such as televisions

and radios, or CCTVs, placed in the vicinity of the pressure port of

a target DPS. The low and high pressure ports are often mounted

in eyesight, and placing the audio source near the target pressure

port requires a brief one-time access. Moreover, audio sources, such

as televisions or CCTVs with speakers, are often installed in NPR

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AWolfinSheep’sClothing:SpreadingDeadlyPathogensUndertheDisguiseofPopularMusicAnomadarshiBarua∗UniversityofCalifornia,IrvineIrvine,CA,USAanomadab@uci.eduYonatanGizachewAchamyeleh∗UniversityofCalifornia,IrvineIrvine,CA,USAyachamye@uci.eduMohammadAbdullahAlFaruqueUniversityofCalifornia,IrvineIrvine,CA,...

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