Uh, good morning everyone. So as Larry just mentioned, today we're gonna talk about an ICS
specific talk and we will discuss, uh, the specific use of some Modbus function by, uh,
Schneider in order to perform some, uh, bad actions on PLC. Just a quick introduction, this
is nothing new. Uh, everything that I'm gonna mention today was discovered, uh, maybe 10
years ago, mostly by, uh, reverse ICS from Digital Bond at the time. However, um, I will try
to show how it is still relevant even in newer PLCs and, uh, also how we can use that to
perform a new kind of attack. So just a few words about me, my name is Arnaud Soulier, I'm
French as you can probably hear. Um, I mostly do pen tests, a bit of research and
development. I'm a manager at WaveStone, that doesn't mean I manage anyone. Um, I really,
really love ICS, really fun to play with and I've given a lot of, um, ICS workshop where I
teach people how to perform, uh, entry level pen testing on ICS at, uh, Black Hat Europe,
Brucon, Defcon, besides Las Vegas. And, um, I also like other things like Active Directory
security and other stuff I'm not gonna talk about today. So I'm not sure that everyone is
familiar with ICS here so I'm just gonna try to give a crash course in 1 minute or something
like that. So ICS mean industrial control systems. Those are the system in charge of, uh,
let's say managing all the automation at plants and factories in all kind of sector. If we
take a look at this diagram you will see that an ICS is composed, um, on the far right side
of sensors and actuators. A sensors will give you an information, for example a switch will
tell you if it's, uh, switched on and off. And, uh, one actuators will perform an action. For
example, if you take the simplest example, it's a light bulb. You see that it emits light or
not. Those physical device, they are managed by PLCs. That's the device we're gonna talk
about today. That stands for programmable logic controllers. And mostly it's an embedded
computer with electrical inputs and outputs. That's the main difference between a standard
computer and a PLC. Those PLCs are then managed by, uh, some classical IT stuff like, uh,
Windows servers and workstation running what we will call today a SCADA software. I'm not
digging into the detail of SCADA versus DCS and stuff like that. Today we're gonna call
that SCADA. And somehow this is connected to the corporate network to get some information or
send some, uh, batch, uh, orders. Okay, so there are a lot of ICS protocols. Today we're
gonna talk about, uh, Modbus. It's one of the most widely used I think, uh, discovered, um,
invented in 1979 by a company that was at the time called Modicon and later bought by
Schneider Electric. Um, it was designed to work over serial lines, um, so RS, uh, 485
mostly. There are two versions of the protocol, the binary and the ASCII. And if you take a
look at a frame format, you will see that it's composed of the address of the PLC. Then what
is called the PDU, the protocol data unit with one function code and the data and, uh, some
kind of cyclic or linear, um, redundancy check to make sure that we have data integrity. So
what do I talk about the frame format? Just to show you that, uh, there is no security
built into the protocol. There is no encryption, there is no authentication. So that was not
really a problem when we were using that over serial lines. However, later they tried to use
Modbus over TCP. So they just removed the integrity checks because that's handled by, uh,
the, uh, TCP, uh, layer. And, uh, a Modbus TCP frame format also has the PDU, so the
function code and the data. And as a transaction identifier, that's, uh, let's say, um, a
random number that is used to make sure that, uh, the request and the response match. A
protocol identifier which is usually, uh, has the value 1, not really useful. The length of
the packet and the unit identifier. Most of the time the unit identifier is set to 1
because we already have the IP address to identify which PLC we talk to. So we do not need
to use this, uh, field. Mostly Modbus is used to perform read and write actions. So here
you have the most function, uh, most common function code. Um, it's mostly used to read
some information. A coil which is 1 byte or, um, a register that is 8 byte. As you can
see, when Modbus was transferred to TCP, they did not added, uh, any kind of security. So
still no security. So this is a protocol that's used for ICS. There is no authentication, no
encryption. You can perform other kind of actions. For example, there are some basic
diagnostic functions built in like the, um, function read device information. Um, that's a
screenshot of, um, this kind of, uh, request to this PLC which is a Schneider M340. As you
can see, we can, uh, know the fact that it's a Schneider Electric PLC and also get the
detailed hardware information. So BMX P34. So that's interesting. But there are other kind
of Modbus function codes that are used and not part of the standard. So we will focus on
the Schneider PLC. So, uh, I do not have knowledge of all the PLCs that are produced by
Schneider. However, I've encoded, uh, several, uh, kind of products. The first one and the,
the oldest are the Quantum 1, then the Premium, then this one, the M340. And then we have
newer, newer models, the TM221 or 241 and the M580. So those PLCs, they are programmed, uh,
by engineers using a specific Schneider software which is called Unity Pro. And, um, what
we're gonna see is that Unity Pro is actually relying on some specific Modbus function code
to discuss with the PLC and to program it. So how do we do that? It's quite simple. You
install a demo PLC, you install Unity Pro, you launch Wireshark and you take a look at the
packet dump. So as you can see, here's a packet dump when I log in to a, to a PLC and I
upload a new program. It runs on top of Modbus TCP. Uh, the function code is 90. It's
already part of the Wireshark de-sector. So as mentioned, uh, the use of Modbus function
code 90 is not something new. It has been known for years. And when I first started working
on it, uh, I had a chat with, um, I think it's Alex Lagut, a Wireshark developer in France,
and he was kind enough to add this to the Wireshark Modbus TCP de-sector. So now if you
take a look at, um, Modbus traffic, you will be able to know when there is, uh, somebody
performing admin actions on a Schneider PLC. Um, something else that's really important, I
mentioned that in the introduction, uh, all of this is already known. The fact that you can
upload a road program to a PLC is known, uh, since at least 2012. It was done by, uh,
reverse ICS. Um, so what I did was during a, an assessment, I think it was maybe 5 years
ago, I was, uh, facing a Schneider PLC so I take a deep look at what, um, uh, Red did and
what I try to do is try to build on that to add additional features or to make the, the
Metasploit modules more reliable. Okay, so now we, we see that using Modbus function called
90 we can do everything that can be done with Unity Pro, the programming software. So what
kind of evil things can we do? First thing, not really offensive, is to gather some
information about the, the PLC and the project and I'm gonna try to demo that. So here on my
setup, just to, to be clear, I have a Schneider PLC M340 and this is my laptop that will host
both the attacking VM and the legitimate, uh, HMI workstation. Well, actually I did not plan
on how I was going to type and, uh, have the mic at the same time. Thanks a lot. Okay, so
the idea is that I'm using a, a new Metasploit module that I just developed this week and, uh,
I'm gonna try to see what kind of information we can gather from, uh, the PLC. And hopefully
it will work. Yes. So as you can see, um, I'm able to get the same information as, uh, using
the Modbus function code, uh, 43. So the BMX is the hardware CPU of the PLC. That's the name
of the project that's on the, the PLC. And from time to time I'm also able to get the host
name running the, the, the name of the workstation running this programming software, the
version of, uh, the Unity software and the comments in this project. I think there are no
comments. That's why we are, do not have anything here. Uh, okay. So that was the, the, the
first thing. Uh, next we can start and stop the PLC. So, uh, that's, does not mean we are
gonna have to shut it on or off, but actually the PLC will stay on. We can still perform admin
action, but it will not execute the program. That's basically what start sub did. I'm not
gonna demo that today. Why? It's quite simple. Uh, there is a module in Metasploit. It works.
It works greatly when you want to stop the PLC, but it does not work so well when you want to
start it again. You actually have to unplug the electrical, uh, plug of the PLC and put it back
again. So in order to, let's say, do not waste too much time today, I'm not gonna demo that,
but it works quite well starting and stopping the PLC. Uh, another thing that I want to show
you is how to download the ladder logic. What I call ladder logic is actually the, the
program that the PLC is executing. So that is also something that Red had worked on, but
during my assessment a few years back, I discovered that it was not working correctly. Why?
It's quite simple. Um, I think he used a demo, uh, program, so really small in size. So he,
there was a misconfiguration with the, the size of a counter in the specific Schneider
protocol. Okay, so here you can see that I'm gonna attempt to download the program and to
store it at this, uh, location. Okay, so there are a few Modbus requests that are sent to the
PLC. The Ethernet card is flashing and in a few seconds we should have the program. It's a
very simple program, just, um, managing a traffic light, so it's quite, uh, it's quite fast.
Okay, so here I have my file. So now what I'm gonna do, I want to make sure that the file that
I downloaded is the real one. So I'm gonna switch to the other VM, which is a, uh, Windows
one. Uh, I'm gonna connect to the PLC. Oh yeah, it's not working. Yes, it works. Uh, I'm gonna
download the project, uh, from the PLC to my PC. Okay, so now I have, I have on my PC the, the
same program as the one running on the PLC using the legitimate software. I'm gonna save that as
an archive on my desktop. Okay. If I take a look at the desktop, I'm gonna try to find the
file. Okay, it's here. I just have to rename, rename it because it's actually a zip file. And if
you take a look inside the zip file, you see that there's a hidden folder called binappli. And in
this file we have, uh, uh, in this folder we have the station.apx file, which, uh, actually the
one, uh, that has the, the PLC ladder logic. So I'm copying this file to, um, uh, to a share to
the other VM. Okay, I'm replacing the file. And if I go back here on my Kali Linux machine, uh,
okay, so I'm actually doing a binary diff between the file I just downloaded and the one that I
just copied from the legitimate software. And as you can see, the files are identical. So the
module works. It's possible to download the ladder logic. Uh, it should be possible to upload
it as well. However, I have the same kind of issue with the counter and the size of the
counter. So at the moment, the module in Metasploit, uh, or the one that I developed does not
work correctly. Okay, so those were the thing that already existed. But since this is Defcon, I
wanted to, to have something, uh, to have something new. Uh, so one feature that was really
interesting to me was the, what we call forcing the outputs. Uh, I don't know if you have
already worked on the PLC. Forcing the outputs is used during the development phase, uh, that
allows you to bypass the control, uh, the, the ladder logic of the PLC and directly set the
outputs to on or off or any kind of, uh, arbitrary value. Um, and that helps you debugging,
uh, especially when working with, uh, other entities. So that's interesting why the way PLCs
are developed, most of the time, um, on the SCADA HMI, you do not read the values of the
outputs. You read the values of some intermediary, uh, variables. So for example, if I go
back on my, um, Windows workstation. So here I'm gonna launch the, the SCADA software. Okay,
so basically this controls the, the, um, the PLC. As you can see, I can switch the lights on
and off. The way it works is that I'm not directly reading the outputs because that's not a
feature, uh, that this, uh, specific software has. What I'm doing is actually, if I take a look
at the code, let me zoom on that. So as you can see here, I have 3, uh, variables, red, green,
and orange, that will set the outputs to, uh, 1 or 0. That's the way it works. So I have
modbus values that are, uh, um, managing the values of the outputs. From what I've been able
to discuss with, uh, people, engineers working in automation, most of the case that's how it
works in ICS. You never use directly, uh, the outputs. You use some kind of intermediary
variables because in real life, uh, you will use some complex function block and it's not as
simple as just, uh, uh, 1, um, 1 switch. Okay, so that's interesting because what happens if I
want to directly modify the, the outputs, uh, what will happen on the HMI screen? Probably
nothing. So that's what I'm gonna demo here. Uh, let me see, okay, I go back to Kelly. So here
I'm just gonna use the other module. I will launch, uh, a specific action that will set, uh,
every output value to 0 then 1 and, um, that for all the 8 outputs that I have on this, uh,
specific, um, PLC. So the idea is that I should be able to modify the real process without the
operator noticing anything on the screen. So that's what I'm gonna try to do. Okay, so the
module is running so at some point we should see the light changing. It should not be, uh, part
of the, the HMI screen. Let's wait a few seconds. Yes. So as you can see I'm switching the, the
first output to 1. But that's not displayed on the screen. Then I'm gonna do the orange one, set
to 1 then 0. But it's gonna stay orange on the screen. There's a 5 second delay that, that may be
a bit much. And the light, the last one will be the green one. No, the orange again. Okay. So as
you can see I was able to barely influence the physical process without having any kind of
information displayed back to the, uh, to the operator. Okay, so that's interesting. Uh, other
topics I'd like to work on in the future is the ability to hot patch the PLC. Because actually
when you program the PLC you have to stop it, upload the program and start it again. So in the
physical process anyone will notice that. However, using Unity 4 you can also hot patch. That
means you can perform some small modification of the ladder logic without having to stop the
PLC. So that's really interesting. And I'd like to have a Metasploit module that does the
same. Uh, for the record I also have another module in the works that does not force the
output's value but the register's value. So you can actually modify any action inside the
ladder logic, uh, as you wish. Okay, so that was true for the premium, the quantum and the M340
PLCs. Uh, what about the new ones? So in 2015 I bought the, the new, uh, released TM221. So
those are entry level PLCs and what I've discovered is that even if they are not programmed by
Unity Pro but another soft, software called SoMachineBasic, they actually still use the same
function code. So even the PLCs released 2 years ago, even if we know that there was no
authentication on admin actions since, since, uh, almost 10 years, uh, the new PLCs still have
the same problem. Uh, however, the, the exploits, they do not work out of the box. You
actually have to perform some kind of modification, change some offsets. So it's
vulnerable but you cannot prove it at the moment. Uh, one of my colleague, Alexandrine,
the, she already had, uh, ported some modification to the Metasploit module so you can now
start and stop those device, uh, without any kind of, uh, authentication directly from
Metasploit. So that was, uh, 3 years ago. Um, I recently learned that the new high end, uh, M580
PLC adds IPSec authentication. So between the engineering station and the PLC. So that's a
good thing. They actually use IPSec not for encryption but only the, uh, uh, authentication
header part. So that allows you to make sure that, uh, if you want to program the PLC, you
have to know the pre-shared key. So that's a good thing. However, that's quite new. Uh, it's
the high end PLC so the, uh, CPU is, uh, at least, uh, I think $4,000. So at the moment I
haven't, do not have the money to have that in my lab. Uh, so I cannot vouch for it. But
that's the good idea, that's a good idea and that's the way things should work. So we can
hope that in the future it will work. However, this is something quite new and you will
probably not see that in plants and factory for, uh, at least 5 to 10 years.
Okay, so what do we do now? Um, is it possible to, let's say, configure the PLC in a way that
allows you to, uh, defeat those kind of attacks? To the extent of my knowledge, no. Uh,
actually there are very few things you can do on a PLC. Uh, I think that on some Schneider
PLCs you can, there is some kind of integrated firewall but it works not like a firewall
because you can actually send a modbus- it's at the application layer, let's say, not at the
network layer. But you could use that to prevent, uh, unauthorized action. Using newer PLC
will work only if you buy the light, the latest one. So it might also be difficult to
implement in, uh, I would say in, uh, existing or legacy environment. And of course what
you can do is perform network security monitoring. As mentioned, those attacks are not
new. Uh, the exploits are new but the vulnerability is known for a long time. So there
are signatures for this modbus function code. So if you're using, uh, any kind of network
security monitoring in your ICS, you will be able to detect any kind of attack. I would say
that you should log anytime, uh, an engineering station logs to a PLC to perform admin
action. And of course if you have an unknown workstation doing modbus, uh, 90 traffic to a
PLC, that should raise a really, really red alert. Okay, so to sum things up, uh, most
China PLCs, uh, that you will find in, uh, ICS, in, uh, assessment are vulnerable for, uh, 10
years to this unauthorized access vulnerability. Uh, attackers can leverage that to do
whatever the hell they want with the PLC, including, uh, forcing directly the outputs which
might allow them to perform some kind of stealthy attacks on your process. So what can
you do? Um, I would say at the moment you have to deal with it. Okay, so before I take any
question, I'd like to say that everything is at this GitHub address at the moment. I really
hope to be able to clean up the code and, uh, do a pull request to Metasploit, but they're
quite picky about code quality and at the moment it's, uh, it's pretty shitty so, uh, in a few
month, uh, I hope to be able to do a pull request to put that directly into Metasploit. Uh,
but you can find that today on GitHub as well as the slides and a few videos of me, uh,
pentesting PLCs. So do you have, uh, any questions? Also, I'd be happy to play with other
kind of PLCs. If you have, for example, Schneider PLC that I do not have, it would be easier
for me to try to understand the protocol. So if you have, uh, uh, M580 or TM241, I'd be
interested in testing that. Or you can also download the modules, test on your own and give
me some feedback on GitHub. I would love that. Okay, so if there are no question, thanks
everyone. And, uh, I'll be around the ICS village, uh, a lot, I think during DEF CON. And if
you are interested into ICS, of course, you just go, uh, across the hall and you will find a
lot of PLCs to play with.