This talk is about my search for a good UPnP hacking tool.
So what we're going to go over today is just some introductions to tell you who I am.
First I'll start talking about what is UPnP and why should you care about UPnP?
Why was I looking for a tool to hack UPnP in the first place?
I'll talk about some of the tools that are out there right now and what I found to be
their shortcomings and why I thought that they weren't quite sufficient.
I will show you a new, an updated tool that I put a lot of updates into and I'll talk
about the features of that.
And throughout we'll do some demos of that functionality and about UPnP in general.
Q&A was going to be in the Discord chat, but I know Discord is down at the moment or there's
some issues with it.
So if that still happens, we'll probably just keep the Q&A here in the Twitch channel.
All right, so who am I?
Real name is Trevor Stavato.
I've been in offensive security for over 10 years.
Different positions, mostly in web app and network pen testing.
A couple of years ago, I founded this cool little company called LabMath Security.
Before I was in hacking, I was a software developer and I did that for a number of years
and then realized all the mistakes I was making once I became a hacker.
I try to be an active member of the security community.
As Sam said, I help do some IoT village stuff in Canada.
I help sometimes in the U.S. as well.
I like to dabble a little bit in RFID.
So we do an RFID village here in Canada.
And I do some red teaming for the pros versus Joe CTF,
which unfortunately didn't happen this year because of all this COVID stuff.
Maybe one of my proudest achievements so far is the DEF CON 26 black badge win at the IoT CTF.
All right, so let's talk about what UPnP is.
So UPnP is Universal Plug and Play.
And it's a protocol defined, I think back in 2008 was the original publication of this protocol,
allowing for devices on network to discover and interact with each other.
It's based around a principle called zero configuration networking.
Really what they wanted to be able to do was to have a device that just plugged into a network,
found other devices and was able to talk to and communicate with the other devices
and have them configure themselves according to their needs
without anybody having any actual input and hands-on keyboard configuration.
Sounds like a great idea to me.
So UPnP is a protocol that uses pretty standard services like HTTP, XML, and SOAP.
And it defines a way for services to describe their functionality and interact with other devices.
A lot of the common uses for this are for network services.
So small office, home office routers will use this for configuring port forwarding.
There's data sharing services for network storage, media streaming, for example, Chromecast,
or some of the original versions of Chromecast use UPnP to initiate the streams.
And it's also used commonly in smart home control,
which will be one of the demos that we're doing later on today.
So in the spec, UPnP talks about kind of six capabilities or six things that are required
for proper UPnP functioning. The first one is addressing.
It's not as important for the tool because we can't really talk to it unless it has a device,
but the device needs a way to get an IP address. And this is typically done through DHCP.
The second one, more interesting to us, is a discovery protocol.
The devices need to be able to advertise their presence on the network, or other devices need
to be able to search for other UPnP devices on the network. So there's a protocol called
Simple Service Discovery Protocol, SSDP, that is used to do this advertisement.
And I'll show one of those requests later and show how that works.
Once you know what devices are on the networks, you need to know what those devices can do.
And then there's a device description XML file that gives this detail. And when the devices
broadcast their presence or another device searches for them, the URL to that XML file
is part of the response that comes back. The next part is control. So once you know
what it can do, you need to know how to control that device. You need to know what endpoint to
send the request to, what parameters you need to include in the request. Once you have this
information, now that's enough information to start interacting with that device.
There are still a couple of other parts to UPnP. The fifth one is event notification. So
you can subscribe to specific state variables on a device. And if that state variable changes,
it'll send a notification to you. And then the last part of UPnP protocol is a presentation.
For the topic of this talk, that's not as important, because that just gets into sort
of regular web app hacking, less UPnP hacking. So we're going to focus on two to five with this
talk. So I'm going to show you just a brief view of a device description and what that kind of
looks like. So over here, I'm going to run a search. And you'll see the discovery message.
And I'll make this bigger, because this might not be easy for people to see.
So there's a discovery message that uses a custom HTTP verb called msearch. It posts to a
broadcast address. And this is just a fixed... this is the same on every network. It's got a
message saying, try SSDP discover, and the service type in this case is SSDP all, which basically
says, all devices respond to me. And you can see the responses come back here from all the
different devices, showing you here is the location of my device description. And it'll
also give you some information about what kind of device it is. So you can see on my network,
there are a couple devices that have a lot of different services. Because we said SSDP all,
all the services are responding separately. So now I'm going to... we're going to take a look at
one of these. And we'll show you what a device description looks like. And make this bigger.
So this here, you can see my setup here on the other screen. I have an Asus router,
I have a WeMo switch, and that is, there's a little lamp plugged into that WeMo switch.
So the device description we're seeing here is for the Asus router. It shows you the model number,
the version numbers, serial number, a lot of information about it. When we get down into
this section, the service list, this is where we see the different services, the UPnP services
that it supports. So it'll show you the URL that you need to send control requests to,
the URL to send event requests to. And it'll also have, not in this one, but in some of them,
it'll have the, oh yeah, no, here it is, the SCDP, so the service controlled
description, so the service description. So if we copy this, and we put this on here,
we'll now put a double X bar, there we go. Now we'll see all the actions that this service
supports, action name, and all the arguments. So we can collapse all this, and you can see there's
gonna be a bunch of actions for this service. And then we get into this server state table that
talks about all the state variables. And some of these won't send events, so the send events is no,
but some of these do. And those are the ones that we can subscribe to. So physical link status
is a variable that we can subscribe to and get notifications when that status changes.
So you can see how this can be used by devices to monitor what's happening in the network and be
able to control it. So that's the overview of how the service descriptions and device
descriptions work and what they look like. So one thing that's missing from this spec
is that there's no authentication. Even on the control endpoints, when you're sending a control
message, they are unauthenticated. It's a very old protocol, as I said, 2008, so they probably
didn't think about that part of it. There have been some updates, some other optional pieces
that you can tack on to add some authentication and some security to it. But those really,
from my experience, I haven't seen any devices that use those. So most of this is just fully
done unauthenticated. So why does this relate to IoT? Why is it in IoT Village? A lot of IoT devices
are using UPnP. It makes them very simple for setup and control. A lot of consumer devices,
they just want to make it simple. You take it home, you plug it in, and it works. So that's
why UPnP is helpful for that. But as a hacker, we can look at what can we do with that. So we can
do things like turning smart home devices on and off. And I'll do a demo later of the Wemo switch
turning that on and off. One of the other things that UPnP has gotten the news a lot for is the
ability to update the router's configuration and open ports on the router so that you can forward
from the WAN side, the internet side, into the internal network. And then, as I said, you can
also control media devices. So I thought IoT has already so many vulnerabilities. There's got to be
some UPnP vulnerabilities, right? So that's why I wanted to look at UPnP as sort of an attack path.
As I said, there's been a couple of notable exploits in the news. Back in 2017, Akamai
released a paper talking about UPnProxy, UPnProxy. Basically, a lot of devices were configured to
expose the UPnP interface on their WAN, on the WAN side. So you could send control events,
things like port forwarding from the WAN side. So somebody on the internet could control your
router and could set port forwarding to get internal access to your network. And even some
of the rules, the way that they were doing the port forwarding, they're not validating the field.
So you could port forward a port on the WAN side and forward it to a completely different URL
somewhere else on the internet. So people were using this as a proxy, as their UPnProxy,
to hide where they're coming from and sort of disguise their attacks.
Back in 2019, there was a pretty famous attack from HackerGiraffe, where they used basically
that same functionality, routers that were allowing configuration on their WAN side,
to port forward to the Chromecast device. And then from there, they could control the
Chromecast device, because it used UPnP as a way to stream a video to it. So they could control
the Chromecast device and put a video of their choosing on. And they decided to put up an
advertisement to subscribe to PewDiePie. So that got a lot of news headlines.
One of the more recent ones that I've come across is this vulnerability called Call Stranger.
And it's a 2020 vulnerability. It's really interesting when you look at this, because
basically what he did is he looked at the UPnP spec and just noticed that there's some
bad design in the spec. So I talked about the event subscription part of this. There's a callback
of the event subscription. So you tell it where to call back when something changes.
But there's no validation at this point done on that callback. So you can have that be some other
address on the internet. You can use it to... you can add query strings on it. So you could use it
for data exfiltration, if you wanted to get stuff out of a network kind of sneakily. There's also
some amplifications type ramifications to this, because you send a very small request,
and the request that comes back or gets forwarded to that notification server is much larger in
size. So you can potentially do some sort of denial of service using that amplification.
So we'll look at that and show you how that's done. So when I went looking for the UPnP tool,
there's basic things that I would want a UPnP tool to do. First, I want it to discover all
the devices on my network. I don't want to have to go out there and look for it. I want this tool
to be able to find them. Once it finds them, it should be able to parse the description, find the
services and actions and events. You know, XML is pretty straightforward and easy to parse. So that
should be straightforward. And then to be able to build and manipulate the UPnP requests, that needs
to be something simple that I can easily do, and potentially, ideally, fuzz that interface.
So let's look at some of the tools that are out there and how I found that they worked. Now,
this isn't an exhaustive presentation of what's out there. These are just the more common ones
that I've come across. The first one is Miranda. And it's available in Kali out of the box.
Has a nice command line syntax, if you like that kind of thing. But on the con side of things,
I found it doesn't always work. In the case, I just ran it yesterday on my home network.
It can find the devices by doing an msearch, but it seems to have trouble parsing some of the
service description files. So it comes back with an empty list of services, and it can't do any
sort of control of the actions. Also, command line syntax, in my opinion, isn't as nice for
interacting with these requests. And I just don't find it as nice to use.
The next tool that I looked at, and I was actually really excited about this tool,
was the Burp UPnP B-Hunter. It's available in the Burp app store. Because UPnP is HTTP based,
XML soap, all that kind of stuff works really well in Burp. And it works really well in Burp's
other tools, like Intruder and Repeater. So I thought this was a great place to have that
kind of functionality. But when I started using it, there were some major problems that I had
where it wouldn't detect all the devices on the network. Some of the devices that I knew
were there, it wasn't picking them up. And sometimes the parsing wasn't working. It wasn't
able to parse the service descriptions and get access to all the different control points.
Lastly, I found the interface just wasn't so easy. My home network, I do have a lot of IoT
devices plugged in. And when I do a UPnP scan, I get back five or six devices. Each of them have
many service descriptions and lots of control endpoints. And the version that's in the app store
right now basically has very little fine-grained control over what requests you send to Intruder
or Repeater. And sometimes even you don't have control over where you send it to. It's either
one or the other. But I was ending up with, you know, a hundred Repeater tabs of requests and
trying to dig through a hundred tabs to find the one request that I wanted to fuzz or test.
It's just not very user-friendly, in my opinion. So, you know, what's a wannabe UPnP hacker guy
like me going to do? As I said, there's other tools. There are things like uFuzz that's based
on Miranda. So it's going to have the same sort of shortcomings that Miranda has. There's some
.NET tools, but I don't really work on a Windows laptop very much. So .NET is not that conducive
for me. So, you know, I was kind of looking at a few different options. I keep looking,
see if there's other tools out there. I build a new tool from scratch or I modify an existing
tool that's already out there. So being Canadian, I turned to my good friend and my neighbor,
Drake, and I said, what should I do? He told me, don't build a new tool from scratch.
You got to modify something that's already existing out there.
So that brings me to my version of Burp's UPnP Hunter. I thought that it had the best sort of,
you know, potential for a tool because of its integration into Burp and some of the other
tools that you can use with Burp. But first we had to get through some of the bugs that
it was facing right now. So the first one, the fact that it didn't detect all the UPnP devices
on the network, I found that this comes down to some devices just don't follow the spec very well.
It was sending the msearch using an ssdp-all, which I showed earlier, and all devices are
supposed to respond to that. But some devices, they just don't. So I added a different msearch.
So it does two msearches, one using ssdp-all and one using another tag called root device.
And only the root device is supposed to respond to that, not all the different services.
That seemed, pardon me, that seemed to work a little bit better for some of the devices that
were on my network. So I was able to find all the devices on my network at that point.
I still had some issues though with parsing in this tool. There was an interesting unsigned
integer conversion error. So Burp is written in Java and Java byte arrays go from negative 127
to positive 127. But Python, which this tool is written in, has byte arrays go from 0 to 256.
So in most characters, that doesn't really matter because you're still in the 0 to 127 range.
But when you get into special characters and you get an assigned byte array from Java going
into Python, things don't work so well. So I had to do some tricks to convert that back to
an unsigned byte array. So that, you know, no matter what we got in the service description,
special characters or not, it wasn't going to work on me. I also found that the control URLs,
the way that it was parsing the control URLs from the device description, it didn't account for the
fact that some devices add query strings to the control URLs. So they have a generic control URL,
they have a query parameter that it uses to determine what service you're trying to talk to.
Without that, it just gave me back a bad request. So I had to modify the tool to actually use the
query string that was part of the control URL. Lastly, there were still other issues with the
parsing. It wasn't actually doing XML parsing in the first version. It was using a regex to try to
search through the XML document to pull out the pieces that it needed.
And if you had an XML document that wasn't structured the way it's expected,
then it wouldn't work. So I switched it to use actual XML parsing because that just makes sense.
I also changed the UI for the tool. Because I didn't want to have to dig through 100 tabs in
repeater, I added some combo boxes where you can now select the IP, the service, and the action.
So you can drill in on the specific request that you want to look at and play with.
I added a full request viewer and editor. So you can look at that and maybe change things
before you send it to intruder or repeater. And you have the option to send it to either.
You're not sort of tied into one or the other like you were in the first version.
And lastly, I added a couple new features to the tool. So I added the ability to subscribe to event notification.
So it parses that service description, looks for state variables that have events turned on,
and then it will build a request for you that you can generate a subscribe request
to subscribe to those state variables. I also added an option to specify the single device
description. So instead of searching your network, you can specify a remote service description.
Searching only works on your local network because you're broadcasting to an address
within your local network. So only devices within that local network are going to work.
But if you go on Shodan, there's a lot of UPnP devices on Shodan that are exposed to the internet.
If you want to play with those, now you can because you can paste that service description
into there directly and load that and get all the actions. I also added some little buttons
so you can view, pull up the service description and SCDP files directly from the tool.
That was kind of more of a convenience for me as I was debugging and trying to figure out
why things weren't working. To easily get to the device description and those files
made it a little bit easier to see what I'm looking at. And now it's demo time. So we'll go through
that tool and show you what it actually does. So UPnP Hunter 2.0. Right now it is not available
in the Burp App Store. I do plan to push it to the Burp App Store at some point later.
I first wanted to wait and give the original author a chance to pull in some of the changes
that I pushed and maybe update the tool from there. He doesn't seem to have the interest
to do that. So I will push this as a separate standalone version. So this is the tool. This
is what it looks like in the Burp tab. And I'm just going to go ahead and start a discovery
on my network. And this will take a few minutes. Because as I said, it's running the
mSearch, reading back all the responses and then parsing out. So on this network,
I have two devices that are running UPnP. This is the ACES router as we saw before.
This one is the Belkin WeMo device. And this is the list of all the service endpoints that
it understands. And if you look at the different actions, these are all the actions within that
service endpoint. So I'll just pull up the SCDP here for a second. And so you can see,
you know, action, get device information. That should be in here somewhere. Yeah,
get device information. And then once you select it, it pulls up the request,
builds out the request in this field here. So you can view it, see what different parameters
it takes. And then you can send that straight to Repeater or to Intruder. And you'll see that
Repeater picked it up. And now it's here. And I can send this request and get device information
from that device. So that's, you know, very basically, that's how it works. So let's show
you why this is cool and, you know, what we can do with this. So one of the things that's very
easy to do with the Belkin WeMo device is controlling its on and off state. So it's
called binary state. So we are going to find the request set binary state. And we can see there's
a few different parameters here. And the parameter values are just filled with fuzz here to tell you
where you can actually put input. And we'll send that to Repeater. We'll take all this fuzz here
stuff out. And the only one that really is needed for most basic operation is the binary state. So
I'm going to set the binary state to one, which should be on. And as you see over here, the light
flips on and I get a response that now the binary state is on and some other information. And now I
can set the binary state back to zero and the light goes off. So very simple, easy control of
the device state through UPnP. Let's talk a little bit about event subscription. So in here, you will
see a subscribe request. And it again uses a custom HTTP verb, subscribe. This is the path
pulled out of the device subscription. And then again, there's a bunch of places where you can
fuzz. Here in this section is where you put the parameters that where you want the callback to
come to. You can set a timeout for how long you want to get notified of those event changes. And
then this is a comma separated list of all the different parameters that this device will give
event notifications for. So I already have one of these queued up over here. Let's see.
So if everything is still working the way it should, I will get a device subscription,
or sorry, event notification here saying the... that is not what I expected. Hang on a sec.
Property change. Property state is zero. Okay. Sorry. That is what I expected.
Now if I go back to the basic event request and I change the state back to one,
now I get another notification coming in on that callback with the binary state is one. So we see
the notifications and how they come back. What's interesting about the notifications and what this
call stranger vulnerability sort of talks about is you can specify multiple endpoints that this
calls back to. One of the neat sort of features of this is that if the first request doesn't... if
the first URL doesn't... it can't reach it, it doesn't get a response from it, then it will try
the next request, the next IP. So you can actually make use of this to do some internal port scanning
of things on the network. If you can access this on the WAN side, for example, you can use this
feature, specify a host and a port, and then specify a host and a port that you know it can
reach. And if you get the callback coming to your IP address, you know that it wasn't able to connect
to the previous one. So that's kind of a fun little thing you can do with the subscribe feature.
But really, that's, I guess, sort of the end of my demonstration of this tool. I think it
can be really powerful, especially being able to send stuff to intruder and do some fuzzing
with this. And I can also show you here that if we just take this device description,
paste it in here, then we get just that device descriptions services. We don't get all the
other. So you can use that as well to sort of narrow down or look at remote ones, like I said.
And I think that is it. So the repository for this is in our GitLab. The link is here.
As I said, I do plan on pushing this to the Verp app store
at some point in the future, but it's just not there right now.