Matt Wixey – Sound Effects Exploring Acoustic Cyberweapons – DEF CON 27 Conference

>>This is Sound Effects,
Exploring Acoustic Cyber-Weapons
with Matt Wixey. [audience cheers and applauds]>>Ok uh hi
everyone. Yes so this is sound
effects exploring acoustic cyber-weapons. Uh my name is
Matt Wixey, I lead security
research for PWC UK cyber security practice. Uh I’m also a
part time PHD student at
University College London which is there, where this work comes
from. Uh prior to joining PWC I
worked in law enforcement in the UK for a few years. And
previously spoken uh at Black
Hat and DefCon and other cons as well. So a few disclaimers
before we get started, this work
was undertaken as part of my PHD research at UCL. Uh it wouldn’t
have been possible without my
supervisors and co-authors for this project, uh Professor Shane
Johnson and Professor Emiliano
De Cristofaro. Uh what you’re gonna see here is presented for
educational purposes only and
um, you’ll also notice throughout this talk that I
mention uh words like caveat and
possibly and potentially quite a lot. Um that’s kinda for two
reasons, the first is not to
kinda spread uh fear, uncertainty and doubt about the
topic of this talk but also
because this is really early first aide research in an area
where there is also uh a really
blurred line between correlation and causation so that’s why
those caveats are there. So why
this talk? Why this subject? Uh so a couple a years ago at
DefCon I did a talk called see
no evil, hear no evil which was about uh using light and sound
uh to exfiltrate data and mess
with drones and bypass air gaps and that kinda thing. And as a
result of that kinda got really
interested in uh in ultrasound and infrasound, kind of
unconventional uh uses of sound
generally. So why should you care about this talk and this
topic? Uh potentially it’s a
novel class of attack which we have done some exp, uh empirical
experimentation on. Uh it’s an
increasing attack surface as well. Uh and it builds on
previous work on malware and
physical harm, acoustic harm more generally, and uh digital
physical crossover attacks. So a
brief bit of background. Um, probably kinda one of the
earliest uh one of the early
examples of digital physical malware was Stuxnet, obviously
in 2010. Um also things like
Mirai, uh the IOT botnet. Um, more recently some work that was
done on things like MRI
machines. Um there have been examples pri, um prior to those
of malware uh accidently uh or
inadvertently affecting physical kit so the Conficker worm in
2008 infected uh hospital
equipment as did Wannacry to some extent. Uh there have been
um vulnerabilities found in
medical implants, things like pacemakers, insulin pumps, that
sort of thing. Um and various
vulnerabilities in vehicles as well which potentially would
allow an attacker to take
control of them um and eventually cause harm. But
typically with kind of research
there’s an indirect relationship between the attack, the effect
uh, and the, uh potential harm
it’s caused. And to some extent what my research focuses on is
trying to take out um one of
those steps and instead looking at malware or attacks that can
directly affect human beings
either psychologically or physically. Uh and some examples
of the kind of things that would
fall under that bracket, uh would be Kevin Poulsen’s report
in 2008 on attackers who
uploaded uh flashing gifs to an epilepsy support forum. Uh and
those gifs flashed in patterns
consistent with those known to induce uh photosensitive
epileptic seizures and a number
of people had seizures as a result. Uh, similarly, uh
Oluwafemi and others in 2013 and
Ronen and Shamir in 2016 looked ay hacking smart light bulbs. Uh
and specifically found that they
could make those flash again in patterns consistent with uh
photosensitive epileptic
seizures. More recently, Rios and Butts in 2017 uh in their
kind of um uh ongoing research
on IOT vulnerabilities found that they could uh attack an IOT
carwash um and cause it to
strike a human being. So when you think about sound as a
weapon, um this isn’t my chart,
um this is a kind of pretty simplistic view uh of how long
you should be exposed to sounds
at certain levels. Um now this uses decibels. Decibels is an
often misunderstood measure of
sound because it’s not an absolute measure, it’s a
relative measure. Depends how
far away you are from the source of the sound. But you can see
when you get up to something
like 115 decibels, really you can only be exposed to it for
around 30 seconds before either
temporary or permanent harm starts to occur. And another
chart, again not mine, just
shows you kind of where some of these sounds are categorized in
terms of the effects they can
have. Um, so starting with um [audience laughs] starting with
uh 50 decibels um you have a
floor fan which is kind of background noise. Lawn mower and
chainsaw, possibly damaging
sounds, again depends how close you are to it. A jet taking off,
uh again depending how close you
are it could cause pain. Um 200 decibels potentially could be an
instant death. And then the
loudest sound known to humanity is the Windows XP startup sound.
[audience laughs] Ok so um,
acoustics and harm and perceptibility. So what can we
hear? So you’ve probably heard
the terms ultrasound and infrasound before. And
traditionally they’re defined as
being sounds which either above or below uh human thresholds of
hearing. Traditionally that
threshold is 20 hertz to 20 kilohertz. Um however it’s a bit
of a misconception um as we’ll
see you can’t kind of put these arbitrary cutoff points here. Um
threshold is very widely and it,
depends a lot from person to person what frequencies we’re
able to hear at what stage in
your life as well. Uh in, in this talk if you see HFN, high
frequency noise, that means
between 17-21 kilohertz. So from near ultrasound, just above true
ultrasound. And if you see LFN
that means 60 to 100 hertz. The problem with um with ultrasound
and infrasound is that basing a
definition on a lack of a property is a problem. Um,
because the mechanisms of people
understanding high and low frequencies or perceiving um
high and low frequencies is not
fully understood. People have reported being able to hear
sounds as low as 1 point 5 hertz
and as high as 25 kilohertz. Um and there’s also been some
research which suggests that at
some level uh we are aware of sounds even as high as kind of
40 kilohertz. Whether that’s
kind of consciously or subconsciously. And there is a
significant variation in
individuals as to what sounds you can hear. It depends on the
volume, it depends on the
background noise, it depends on the environment you’re in. So
what the walls are made of for
example. Um, you may perceive sounds in different ways to
other people so with low
frequency sounds you may feel it more as a vibration than
anything else. Um you may
perceive what are called audible subharmonics, which are kind of,
you can think about them as kind
of side effects of a dominant frequency. Um and as you um grow
older your ability to hear
higher frequencies declines. Um so younger people, children um
are much more likely to be able
to hear higher frequencies than adults. Now there have been a
lot of reports here, adverse
effects with high and low frequency noise. Um these do
come with a lot of caveats, um
so bear that in mind. Um, the susceptibility from person to
person will differ uh, as we
said, um particularly with age as well, um there are some
reports to suggest that uh
higher frequencies can have an adverse effect on hearing. It
could cause something called a
temporary threshold shift which is where your kind of audible
range will uh will shift
temporarily. Um at more uh uh um increased volumes and amplitudes
there have been reports of
physiological changes as a result of high frequency noise
including things like cardiac
neurosis, hypotension and functional changes in
cardiovascular and central
nervous systems. Psychologically high frequency noise has been
reported to cause nausea,
fatigue and headaches, tinnitus and ear pain, irritation um and
decreased amounts of
concentration. These are subjective effects so bear that
in mind. Uh with low frequency
noise it’s um been associated with temporary threshold shifts
um with heart ailments and
insomnia and with elevated cortisol levels. And
psychologically the most common
uh reported effect of low frequency noise is annoyance. Or
irritation. But it has also been
associated with headaches and palpitations, uh deterioration
in performance, um depressive
symptoms and distress, and interestingly these effects have
been reported even at very
moderate levels of sound. Um so somewhere between 40 to fo, 45
decibels. The caveats I
mentioned with all of these adverse effects, if you go back
and look at the papers, uh the
date is often anecdotal. Um it’s often done through the form of
questionnaires or surveys after
the fact. Uh very easily misinterpreted. We don’t always
know uh the noise dose, which is
the um, amount of time that someone’s been exposed to these
frequencies and at what level.
Um and many researchers have found that these effects are not
reproducible in a lab
environment. Uh and there’s a number of reasons why that could
be. Um the first is that there
are ethical restrictions quite rightly placed on researchers
exposing human subjects to
sounds which they have good reason to believe could cause
harm. Um so in a lab environment
those levels would be attenuated um and therefore might not cause
the effects that have been
reported in the literature. The other example is that some
people may have experienced
something called a nocebo effect so they either believe uh
they’ve been exposed to a
certain uh level of noise or they are being exposed to it and
expireen, the, experiencing
these symptoms but the two might not necessarily be related. That
being said, there is a
significant base uh evidence base to suggest that in at least
a subset of the population, high
and low frequencies can cause some adverse effects. As a
result of that uh a lot of
researchers and organizations have developed exposure
guidelines which are uh a
basically kind of a um define the maximum levels at which you
should be exposed to sounds of
particular frequencies. Now there are problems with these,
uh there are uh big differences
in the way that they’re calculated and implemented.
Typically they focus solely on
the workplace. They don’t focus on the homes or public spaces or
schools. Um they’re often based
on very small samples and those samples are most often uh adult
males. So they don’t take into
account children, for example, who as I said can here uh higher
frequencies that are um, much
mo, they’re much more likely to hear higher frequencies than
adults. This is a compendium of
some of these guidelines. Uh this was compiled by uh an
academic called Timothy
Leighton. And you can see across the top you’ve got the various
different frequencies. Now these
are not precise frequencies that the sensor of a, a range of
frequencies called a third
octave band um and then on the left you can see the uh
guidelines that go all the way
back from the mid 60’s right up to 2015. This isn’t necessarily
an exhaustive list but just by
looking at this you can see two things. The first is that um, as
you increase the frequency the
maximum exposure goes up to some extent. The second is there’s
big disparities between some of
these numbers because they’re calculated in different ways. So
just a quick thing on weighting
as well. If you’ve ever done any sound measurement you’ll be
familiar with weighting. Uh
sound weighting is a way to either attenuate or emphasize
certain frequencies when you’re
doing a measurement of sound. Um so A weighting is the most
commonly used if you buy a sound
level meter online or a hardware store or somewhere like that, it
will most probably use A
weighting. Um and as you can see A weighting uh significantly
underestimates lower frequency
sound um because ih, it kind of the curve decays away at the
start. And then uh it works to
underestimate higher frequency sound that decays away at the
end. Um C weighting is another
example, you can see there’s less of a decay but it still
does decay to some extent. Um
you’ve also got Z weighting which is uh mostly what we used
for this experiment because it’s
a flat frequency response so it doesn’t attenuate or emphasize.
So um, yea as I said, so with uh
A weighting it’s inappropriate for measuring higher frequency
noise because it underestimates
those higher frequencies. Um so Z weighting is probably much
more appropriate. With low
frequency noise there are less guidelines available, fewer
guidelines available. Um a
possible reason for that might be that the main effects of low
frequency noise are subjective
at moderate levels. Um but again, even with the ones that
have been published, the
methodology used to calculate them and implement them differs
a lot. So uh for this experiment
we used a reference curve proposed by Defra which um took
into account a lot of previously
published curves. Um measurements of infrasound
specifically use something
called G weighting which is a nicer standard specifically for
infrasound. Because we were um
going higher than that we didn’t use G weighting. So this is the
uh the guideline for low
frequency noise published by uh Moorhouse. Um and as you can see
some of these levels are, are
pretty low um, particularly when you get to kind of 50 hertz, 63
hertz um you’re talking about
kind of 43, 42 decibels, something like that. [speaker
sniffs] Ok uh so some previous
work looking at sound in security research. One of the
most common uh uses of high
frequency noise particularly in security research has been as a
covert communications channel.
Um so Deshotels in 2014, Hanspach and Goetz also 2014,
looked at kind of covert mesh
networks and how uh devices could communicate silently with
each other using high frequency
noise. I at my DefCon talk a couple of years ago I did a
similar thing um with eggat
bypasses and exfiltrating data. Um and an interesting kind of
finding from a lot of this
research is that many consumer devices um are capable of
emitting high frequency noise
even up to kind of ultrasonic levels. There’s also been a
research looking at the
disruption of echolocation systems which use ultrasound. Um
so again in that DefCon talk I
showed that with drones. Um Yan and others in 2016 looked at it
through Tesla vehicles. Um
Bolton and others in 2018 looked at corrupting data being written
to hard disk drives using both
high frequency and kind of audible audio. And then uh
there’s been a number of studies
on looking at ultrasonic tracking beacons as well which
are used for uh for targeted
marketing. So some questions I always get asked um before we
kind of get into the, the main
bit of the um, uh the talk. First is the brown note. Um I
can, I, I can hear some laughs
so I, I know some people are familiar with the brown note. If
you’re not familiar with it,
it’s this kind of mythical tone or mythical frequency [speaker
sniffs] that causes people to
lose control of their bowels, hence the name. Um, in reality
um no one’s kind of been able to
find this, this mythical frequency. Um part of the reason
for that probably is that um any
sound potentially, if it’s loud enough, could cause you to feel
sick, could cause your body to
vibrate and potentially have that effect. Um but there’s no
kind of one frequency that would
work for everybody. If you’re kind of playing sounds at that
volume, you’ve probably got kind
of bigger pr, uh bigger worries basically. Um another one I get
asked about as well is the link
between infrasound and the paranormal. Um sometimes the
infrasound is referred to as
like the ghost frequency or the horror frequency. Um it’s often,
well it’s, it has been used in
things like horror games and horror movies as well. Um, I’d
kind of direct you to a couple
of really interesting papers on this. Tandy in 2000 and Parsons
and others in 2008 who um looked
at the possibility of infrasound at resonant frequencies causing
people to have hallucinations um
also kind of sense a presence in areas associated with paranormal
experiences. Um it’s this object
that gets debated a lot um in that, in that field but it worth
kind of having a read over. Um
and the last one is the US Embassy in Cuba and kind of what
happened there. Um I would
direct you to a paper by Timothy Leighton in 2018 which goes into
some detail about um the sounds
that were recorded in that area and um the possibility or not of
that being uh a sonic attack. So
when it comes to kind of acoustic weapons in general
there are a lot of
misunderstandings around them and a lot of myths. Um as
researchers have noted there are
kind of significant practical issues associated with actually
deploying them. Um which uh to a
large extent applies to this research as well. So the fact
that attackers can cause
something like threshold shifts is probably not of interest to
them generally. Um and it’s
really challenging to cause kind of directional targeted effects
with acoustic weapons. With low
frequency noise uh that can propagate very easily, can
spread over miles potentially.
Um but overseas got very low directionality as a result, and
uh you would need to build
massive kind of audio equipment to be able to do that. With high
frequency it’s got very low
propagation, it doesn’t deal with obstacles well um which is
why it’s used for echolocation
because it bounces off of objects. Um so again there’s,
there’s uh an issue there. So um
moving on to our experiment. Um so this is kind of how we built
the um uh the hypothesis for
this. So we said, ok given that some high frequencies and some
low frequencies might be
imperceptible to at least a subset of the population. And
given that above certain levels
they may be associated with adverse effects. And given that
some consumer equipment has been
shown that it can uh emit at least high frequency noise,
possibly low frequency noise as
well, is it possible, is it feasible for an attacker to
develop malware that can cause a
targeted device to emit these frequencies at levels exceeding
those in some of these maximum
guidelines and therefore potentially cause adverse
effects? So a rough outline of
what we did is we developed uh attacks and malware. Pretty kind
of trivial um malware targeted
at certain devices which was able to control the system
volume and the speaker output of
those devices and as a result play wave files containing
certain frequencies which we
then measured with a sound level meter and compared that, that,
compared that output um to
maximum permissible levels. So we didn’t use any human subjects
for this experiment, um because
of ethical restrictions uh quite rightly. Um we did a full risk
assessment um we had various
safety precautions, we wore ear defenders, we used an anechoic
chamber which I’ll talk about in
a bit. Um and we’re not releasing either code of the
attacks that we did or the
brands or models that we tested these attacks on. So some
scenarios where an attacker
might want to use this, and again this is kind of caveatic
quite heavily, um if they were
seeking to affect the performance of productivity of
targeted or generally uh
employees or staff of organization um or at scale. Um
targeted harassment of certain
individuals or potentially as kind of low grade uh cyber
weapons that could have some
physical effect. Uh worth noting that, you know, if an attacker
is in a position to execute code
on a device then there are more likely going to be things that
they’re more interested in
doing. And even when it comes to sound uh there may be things
that they’re more interested in
doing um than this attack so they may be more interested in
kind of um, you know, C two
channels with that um or something else. So just um a
description of some of the
devices we tested on the left hand side. A laptop, a phone, a
bluetooth speaker, a smart
speaker, a pair of over ear headphones, uh a vehicle mounted
public address system, a
parametric speaker and a vibration speaker. And um you
can see some of the attack
vectors and rather this was kind of remote or local. Uh this was
our anechoic chamber. Um has
anyone ever been in an anechoic chamber before? Oh wow. Ok quite
a few people. It’s weird, right?
Like, really weird. Um so if you havent been, um I really
recommend you, if you get the
chance to do it, do it. Um so basically an anechoic chamber is
a sound proofed environment but
it’s designed specifically to get rid of echoes. Um so these
kind of wedges on the walls are
fiberglass wedges that, that um bounce echoes back and forth
between them so that they
dissipate. Um and essentially what this means is you can be in
this room and the ambient noise
level is below the threshold of human hearing so it is kind of
one of the quietest places in
the world. Um you can hear your own heart beating, if you kind
of move your head you can hear
like your spine creaking in your neck. Although that kind of
might be more something that I
should get checked out um [speaker and audience laugh] But
um. Yeah. Um so it’s really
cool. Um and what’s kind of really kind of creepy and cool
about it is um if you kind of
close your eyes or you turn the lights off then uh acoustically
an anechoic chamber is an
infinite space because there’s no walls or obstacles to bounce
sound off, uh which I just think
is really cool. Um so for our uh Windows malware, which is on
laptops, we embedded these tones
as wave files. We had a really trivial C two channel and all
the malware did uh was it would
get a command to play a certain frequency, it would increase the
system volume of the laptop to
100 percent, play the tone for 10 minutes and then restore the
volume afterwards. Android
malware did exactly the same thing. Our smart speaker, uh the
one we used had a known
vulnerability um that allowed us to control the audio. So for
this to work in practice the
attacker would need to either be on the local network um or
attack an exposed speaker on the
internet or do DNS rebinding or something like that. Um there
was a python script we used to
scan for speakers on the local network and if inactive stream
returned from an attacker
control web server. The headphones, um were over ear
headphones connected to laptop
over bluetooth. Because they’re headphones we placed these much
closer to the sound level meter.
Uh we had vibration speakers which are really cool if you
haven’t used these before. Um so
these don’t have a diaphragm cone. Instead they have like a
coil on a movable plate so
whatever surface you use, whatever surface you put them
on, that becomes um the kind of
the source of the sound if you like. Um parametric speakers,
again these are really cool if
you get a chance to play with these. So these use ultrasonic
carrier wavs at 40 kilohertz. Um
meaning that you can use them for kind of qua, high intensity
directional audio. So kind of
like a beam of sound. Um the one we tested didn’t have smart
capabilities. Um but given that
it is fairly low profile and fairly uh low cost and that it
can be directional, it might be
attractive to an attacker as like a portable acoustic-weapon.
Um a vehicle mounted public
address system. So this didn’t have any network uh interfaces
instead it also plays audio from
an inserted storage device you would need physical access um to
it. Some additional attacks that
we thought of but didn’t test, the first is using uh the HTML5
audio tag to autoplay audio. Um
so this would involve like uh a social engineering attack with
an attacker getting a victim to
uh a website and have the sound play automatically. Um this
would obviously depend on the,
the currently set system volume. Um so not guaranteed to work.
And then [speaker clears throat]
we also used um manipulation of pre-existing audio. So this
would be uh either something
where an attacker has access to like your uh I guess your music
collection or something or where
they’re kind of creating a YouTube video that they know
people are gonna watch. And what
you would do here is take the legitimate audio, lower the
amplitude of it and then insert
a very high amplitude, uh high frequency or low frequency sound
um which would look like this uh
second picture here. So the kind of intended effect of this is
that the victim, uh using their
headphones or speakers or whatever, would turn the sound
up so they can hear the
legitimate audio and then inadvertently expose themselves
to high levels of whatever
frequency it is. Uh just another illustration of that there. So
for measurement we use class one
sound level meters. Um these are precision grade, they’re spot
calibrated, uh they’re really,
really expensive to buy um but we hired them. Um so we hired
one for the low frequencies, one
for the um uh high frequencies. Um and if you ever feel like you
don’t have enough excitement in
your life, um have uh a courier call you and tell them that they
don’t have any record of you
sending this stuff back um and that you might owe a company
20,000 pounds and it puts
everything else in, in perspective. [audience laughs]
Um so we placed each device in
the anechoic chamber with our sound level meter and in viral
attacks we played certain
frequencies um for 10 minutes. We also measured the surface
temperature of each device
before and after the attack because there was some anecdotal
evidence that um, or some uh
anecdotes to suggest that particularly with higher
frequencies, devices could heat
up if they were playing high frequency noises. So we used Z
weighting for the measurement.
Um the only thing we didn’t use Z weighting for was for
measurements at 21 kilohertz
because that’s outside the range of uh Z weighting so we used the
proprietary high pass filter for
that. And these are the results um for higher frequency noise.
So instances where the levels
are um above those in maximum guidelines are in bold. So you
can see the smart speaker at 17
kilohertz and the headphones at 17 kilohertz um both exceeded
those maximum guidelines. And
then the parametric speaker did the same for 17 kilohertz, for
21 kilohertz and for 40
kilohertz as well. Now uh what we’re comparing to here is a
mean average of that big list of
uh guidelines I showed you earlier. Um that was in the
paper by Timothy Leighton. So
you can see things like the laptop and the phone are not
capable of producing sound
exceeding those maximum guidelines so it’s a minority of
devices um in a minority of
frequencies that are capable of doing this. With low frequency
noise uh similar story. So again
a minority of devices. Here it was the bluetooth speaker at two
of those frequencies, a smart
speaker at all three and the headphones at 100 hertz. Now um,
particularly when you get to
kind of the upper range of um the, this, this kind of low
frequency noise, this might be
more audible um and will therefore be less suitable as
kind of a covert attack. Um and
I’ll speak a bit about aud, audability uh in a minute. Some
other results of interest, so
the vibration speaker uh is no good for low frequency because
it vibrates so much that it
falls over. Um so everytime we opened the, the chamber door the
speaker was lying on the floor.
Um the smart speaker, uh when we opened the chamber it was a
really strong smell of burning
plastic. Um and when we kind of uh tested this um we found that
it was actually permanently
damaged. So this is kind of what happened in the 10 minutes um
that this smart speaker was
being tested. You could see the damage starts to occur in like
the second minute this was at uh
17 kilohertz. After five minutes of some sort of critical event
where a component burns out. And
then immediately there the decibel level drops uh and never
recovers. And what we had
actually found was that we had permanently damaged the speaker.
Um and we had made it unable to
reproduce frequencies above five kilohertz. Um so we took
recordings of music um before we
did the test and after we did the test and looked at the
spectrograms uh and on the top
is before the test and on the bottom is after the test. So uh
this is a permanent effect as
well so we’ve kind of permanently impaired that
speaker. Um I’d love to be able
to play it to you, because it’s copyrighted I can’t.Um but it’s,
kind of sounds like someone um
singing like under water or in kind of like a metal uh tank or
something like that. So it kind
of really makes a difference, the audio quality. So we
reported that to the
manufacturers who were really responsive and they told us the
um updates have been rolled out
to addressed it. To address it, sorry. Um now looking at audible
components because this is kind
of a key thing for this attack, um part of kind of the premise
of this as a successful attack
is relying on the fact that users wouldn’t be able to hear
it so depending on the device
you get more or less audible components in kind of audible
ranges. If you look at
headphones for example, this big spike to the right is the target
frequency which was 17 kilohertz
so that’s kind of an intended effect. Um and then you can see
to the left you’ve got kind of
um uh different frequencies there. Um which are pretty low
so if you’re wearing headphones
and this happens you might kind of notice something, it might
kind of appear as kind of
distortion or popping or something like that but um it
wouldn’t be that noticeable.
Conversely if you look at the parametric speaker um the
intended tone is still high but
there are um, much higher levels of other more audible
frequencies which means this
would be kind of less suited for some kind of stealthy attack. So
implications of this with the
headphones um, that it’s a significant concern because
headphones are increasingly
used. Particularly like by young people at high volumes and to
some extent they’re device
agnostic so you can kind of plug, plug it into a laptop or a
phone or something. Um it might
be possible for an attacker to kind of in, encr, um improve
that malware by for instance
only triggering certain frequencies when uh headphones
are connected um so when that
kind of device registers. Um with the parametric speaker um
it does produce a lot of audible
components but it might be attractive to some attackers as
kind of a portable low cost
acoustic weapon. In any case the fact that it’s using kind of
those ultrasonic courier wavs at
40 kilohertz at pretty high levels means that it could be a
uh public health risk. With the
bluetooth and smart speakers um, more difficult to attack. With
the bluetooth speakers you would
obviously need to kind of pair with them um with the smart
speakers though um we could
permanently damage them with a high frequency noise um
potentially that burning out of
components could be a fire hazard as well um and other
models might be vulnerable. So
in terms of feasibility um the attacks that we discovered were
viable on a minority of devices.
So out of the, the kind of 10 tests that we did you’re talking
about kind of a handful of two
to four devices. Um for this attack to succeed you’re relying
on attackers not, oh sorry, on
victims not perceiving uh the sound, on them being susceptible
to the adverse effects of that
sound um and for them being exposed for long enough to that
sound for it to have an effect.
Remember that our tests were only 10 minutes. So for example
if I kind of played a 20
kilohertz tone in this room now uh, you know, a fairly high
level, um some of you would hear
it and, and not be affected by it, some of you would hear it
and probably feel uncomfortable,
some of you wouldn’t hear it and wouldn’t notice, some of you
wouldn’t hear it and might feel
uncomfortable. So it’s a real kind of spectrum um so yea it’s
kind of a lot of obstacles for
an attacker to overcome for this um for this attack to work. And
as I said some attacks require
kind of physical or local access as well. And crucially attackers
might be interested or more
interested in other avenues. Um so if they have kind of code
execution on a laptop for
instance or a phone, it’s likely that there’s other stuff they’re
interested in. Um ok so moving
on to countermeasures. So uh Deshotels in 2014 uh suggested a
number of kind of applicable
countermeasures for these kind of attacks. The first is to
limit the frequency range of
speakers. So many speakers have a frequency range that’s uh goes
up to kind of 20 kilohertz or
above. Um which in most cases is not needed uh depending on what
you’re using them for. Uh
visibly alerting users when speakers are in use by an app or
uh a software program. Doing
some kind of filtering uh during processing to remove high or low
frequency noise if it’s not
needed. And uh with mobiles specifically, some kind of
permissions restriction so that
if an app wants to use the speaker you have to kind of
explicitly grant it permission
to do so. On the heuristic side um it’s very rare that an
application, a legitimate
application, will need access to volume levels. We kind of
thought of uh a few examples so
one would be like a muting app for instance. And there are some
legitimate uses potentially for
ultrasounds so Google Nearby Messages uses um ultrasound in
addition to some other commerce
channels. Um but generally speaking um there’s kind of not
many legitimate use cases for
that. You can monitor the environment for high or low
frequency noise. Um so most
consumer sound level meters will not go as high or low um as the
levels we tested and you do need
specialist equipment. That being said, there are a couple of
android apps that we used in our
pilot study. A ultrasound detector and infrasound detector
which we used with the, a pretty
cheap, external microphone for the android. Um and there is
some studies that suggest um
that one of the smartphones might be ok for occupational
noise measurement at least um as
long as you kind of accept that there are caveats with that and
limitations and that you won’t
necessarily get a, a, 100 percent accurate result. Uh we
developed a proof of concept uh
Windows program um that listens to sound uh coming in from your
laptop microphone and pops up an
alert if it hears frequencies uh above a certain level and above
a certain amplitude. Um it’s
adapted from another open source application. Um we are gonna
kind of release this on GitHub
in uh either this evening or tomorrow morning but obviously
don’t use it to evaluate if
there’s actual risk of uh damage or adverse effects to you um or
for safety compliance
assessments. If that’s something you want to do then you should
really be speaking to a trained
professional who’s got the right equipment. Um but the uh
application will be available
there. It does, it’s accuracy and its kind of performance does
depend a lot on the uh
microphone you’re using and the sound quality you’re using and
that kind of stuff. Um but if
you wanna have a play with it and kind of see how it works
then uh please do. At the um at
the policy level um it’s really important that, uh I think, that
these guidelines are reviewed um
and that there’s some kind of standardization um put in place
for these. Um because as noted
before they’re often inadequate due to their methodology. The
fact that they underestimate
certain frequencies because of the weighting that’s been used.
Um, the fact that they uh
predominantly around occupational context, and that
the samples are very small and
based on adult men, um and in no way kind of um give you any kind
of uh indication if you’re
somewhere outside of an occupational context as to what
sounds are kind of tolerable for
health. Um depending on what area of the country you’re in,
sorry, depending on what area of
the world you’re in um you might have legislation that pertains
to uh sound exposure um whether
it’s low frequency, high frequency or just in general. Um
and ideally your employers would
um as uh a result of that conduct regular checks. So uh to
sum up then. Um this was a first
stage bit of research uh on a very small scale. We looked over
a limited number of devices, we
looked at very short exposure times of 10 minutes um without
human experimentation. There’s
also the note that, like the smart speaker, uh if a device is
forced to continually play high
or low frequency noise then it may burn out anyway um but it
may take kind of several days
for that to happen. Um so we also didn’t do any human
experimentation on uh
perceptibility as to whether uh humans would be, actually be
able to hear this sound. And
that’s just a kind of limitation reassociation in the field
generally. Um because of kind of
ethical concerns. So more research is definitely needed on
uh the risk of high frequency
and low frequency noise. Um that can include like a wider range
of equipment. Um so in addition
to testing um the devices that we tested you could look at
things like IP phones for
example and it wouldn’t necessarily have to be an attack
against them it might just be
kind of injecting uh tones into a conversation um you could look
at kind of uh attacks on a
larger scale. Whether that’s something like uh a kind of uh
worm attack against, you know,
50 laptops in a, in a sound proofed environment. Whether
it’s looking at kind of big
devices like um public address systems um or on a big scale
though logistically obviously
that would come with some challenges. Um testing it’s
overheating effects on the
devices would be really cool to see if that um that’s something
that’s common across a lot of
speakers. Um some more work on countermeasures so, you know,
one of the encouraging things
about this research is the uh whilst the attacks we developed
are pretty trivial, there are a
lot of caveats around it and the countermeasures are also
trivial. Um [stutters] in, in,
in many um cases so that’s kind of encouraging as well.
Obviously the ethical
restrictions to make kind of extrapolation to real world
effects pretty challenging. Um
it’s difficult to be able to say whether or not these attacks
would actually allow you or
allow an attacker to have any effect on people um because
there are so many variables. Um
so we’ve only really kind of scratched the surface in terms
of what can be done in this
field. Um so definitely if you’re kind of interested in
this field, you want to kind of
chat about it a bit more then, then get in touch with me. So
just a somewhat, um so it’s
likely that um attackers might become increasingly interested
in leveraging vulnerabilities
against humans um and kind of having digital physical effects.
Certainly the attack surface for
these devices is likely to grow and potentially any device with
a speaker um obviously depending
on, on kind of it’s sound card and, and um complexity could be
used for this kind of attack. Um
[speaker clears throat] and crucially the lack of consensus
from kind of adequate safety
guidelines is a real challenge. However, as I said, kind of
countermeasures are available.
They will work um and the real world consequences of this is
attack is something that is yet
to be uh ascertained. So um thank you very much. Um if you
wanna get in touch with me
that’s my Twitter handle and my email address. Um I’m gonna take
questions uh at the far end of
the hall, uh of the hallway. Um if you’re interested in any of
this stuff there is uh an
exhaustive list of references at the end of this slide um at the
end of this slide deck um which
cover kind of acoustic weapons, ultrasound, infrasound, human
effects of those um and various
other bits and pieces as well. Um I can play with more
references if you’re interested
um but there you go, so some more reading for you. So um
thank you very much for
listening um and as I said I’ll take questions out in the back.
And thank you very much.
[audience applause]

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