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If you don't configure your network properly, it's very easy for someone using Kali Linux or another

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type of hacking tool to exhaust the IP addresses in a DHCP pool, set up a rogue DHCP server, and then allocate

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IP addresses to clients in a incorrect subnet

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and what I'm going to show you in this video is how to do that, but also show you how to set up the Kali

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Linux host as the default gateway so that traffic from PCs is sent via Kali Linux to the Internet or

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to other devices in the network so that we can implement a man-in-the-middle attack.

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DHCP, or dynamic host configuration protocol is a fundamental building block in networks today and administrator

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which could be you will configure a pool or scope, which is a range of IP addresses that are allocated

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to hosts in a specific subnet.

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Hosts will send a broadcast typically to request an IP address from a DHCP server, and the DHCP server will

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allocate the IP address to the client.

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Have a look at this video, which I've linked here below.

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If you want to learn more about the fundamentals of DHCP, in that video I'll show you how DHCP is configured,

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how IP addresses are allocated to clients.

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I'll show you through

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Wireshark captures, how messages are sent from a client to server and from a server to a client.

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Now, a quick summary of what we are going to do in this video.

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We're going to hack DHCP, we're going to exhaust a DHCP pool or DHCP scope.

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So that's the first attack.

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We're going to set up a rogue DHCP server to allocate IP addresses from the fake subnet, 

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second attack, third attack

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we're going to set the default gateway of clients to Kali Linux.

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So when they get an IP address from the rogue subnet, they're going to see the default gateway as the

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Linux host

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and that allows us to implement a man-in-the middle attack.

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So for text right there, then we'll use Wireshark to sniff passwords on the network.

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You need to be careful when you configure your network using protocol such as DHCP, make sure that you

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configure your network securely and properly.

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Otherwise, it's very easy to hack networks that run DHCP.

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Now this is one of multiple videos where I'm showing you how to hack networks using Kali Linux.

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I don't just want to show you how to break networks.

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I want to show you how to protect networks and I'll show you how to do that in subsequent videos

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in this series. In previous videos in the series, I showed you how to hack a physical Cisco switch

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but I'm traveling at the moment, so I don't want to carry a whole bunch of equipment around with me.

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So what I've done is taken that switch or logically, taken that switch and put it into the cloud.

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In this example, I'm using EveNG and I've got a Cisco switch as well as a Cisco router.

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I've got a Windows 10 computer and I've got Kali Linux.

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These devices are connected to the Internet.

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This network is running in the cloud

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but you could simulate this network on your laptop using GNS3 or EveNG or Cisco VIRL.

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In this example, the switch is running a Cisco VIRL iOS image.

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The router is running a Cisco VIRL image as well.

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Have a look at my EVE-NG videos or my GNS3 videos, 

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if you want to learn more about how to virtualize networks on your laptop or how to virtualize them

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in the cloud.

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So let's start with the switch

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and here's my console to the switch.

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Now, in this example, I'm currently in South Africa, so my connection may be a bit slow to the Northern

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Hemisphere.

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Hopefully it won't affect this lab

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but notice I've connected to a switch, show version shows me that this is a Cisco vios layer 2 switch

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running version 15.2.

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Now, don't worry too much about the details of the switch.

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This is a Cisco switch, but any switch could be used in this topology.

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I'm also using a Cisco router, but again, you could use any router here if you wanted to.

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So this Cisco router, type show version is a Cisco ios V router running version 15.6 1T.

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The reason I'm using a router here is I want to set up this router as a DHCP server.

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So if I type show run, that shows me the running configuration of this device and what I want to point

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out here is I've configured a DHCP pool, a DHCP pool in Cisco terminology is very similar to a scope.

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So it's a range of IP addresses that we're going to allocate to clients in our network.

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The subnet that's going to be allocated is 10.1.1.0/24.

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So /24 mask is being used.

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This is the default gateway.

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That is the IP address of the router.

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I've set the DNS server to Google, scrolling down,

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notice this is the IP address of the Cisco router.

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At the moment, this device has its interface shut down.

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So what I'll do is no shut that.

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That basically enables it.

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I'll also enable the connection to the Internet.

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Going back to my topology this interface on the router connects me to my internal network and this

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interface connects me to the Internet.

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So I'll type end here, show IP interface brief.

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This is the IP address on the internal interface, interfaces up, up, that means that it's working.

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This interface is connected to the Internet.

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It's using DHCP.

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So this router should be able to, as an example, ping Google.com, which it can and I'll save

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the configuration of the router.

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Now, again, you don't have to use a Cisco switch or a Cisco router.

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The reason I want to use the Cisco switch here is Cisco switches support something called DHCP Snooping

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which allows me to stop these kinds of attacks in a network.

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I haven't configured anything on the switch at the moment, but in subsequent videos, I'll show you

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how to stop this attack

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but I firstly want to show you what's possible using Kali Linux.

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So I'll open up a console to Kali.

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I'm not going to get into the debate about the correct way to pronounce Kali.

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Different people pronounce it differently, but for the moment, that's the way I'm going to pronounce

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it.

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OK, so here's my Kali Linux host, let's check if it got an IP address, it may not have got an

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IP address because the routers interface was shut down.

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I'll use more here rather than simply showing all the output

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and what you'll notice is this device has this IP address, 10.1.1.3, show IP DHCP bindings on the

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Cisco router.

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We can see that this IP address has been allocated to this Mac address, this command show, IP DHCP

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binding basically shows us which IP addresses have been allocated to which Mac addresses.

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So this is the Mac address that Kali is supposedly using, 50001.0002.

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0000 and back

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in Kali, we can see that is the Mac address of this Ethernet interface.

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Okay, so what I'm going to do now is start Yersenia using a graphical user interface.

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In a previous video, which I've linked here, I showed you how to install this on Kali Linux.

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I also showed you how to implement or use lyer 2 attacks using Yersenia

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but in this example, I'm going to show you how to use this for DHCP attacks and we're told that this is an

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alpha version.

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That's ok, so I'm going to click OK, and I'm going to go to DHCP.

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We can see some options here

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but what I want to do is launch a DHCP attack.

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So click launch attack

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and we are going to send discover packets using Denial-of-service, now before I do that on the router, show

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IP DHCP binding.

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We only have one IP address allocated to a client.

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Now, the reason why the Windows host hasn't got an IP address yet is it's currently off.

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I haven't started the Windows host at this point.

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So again, show IP DHCP binding on the Cisco router.

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Only one IP address has been allocated.

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So in Kali, I'm going to click OK to start a discover denial of service attack

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and what you'll see is a whole bunch of DHCP messages are being sent into the network.

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You can see this packet-count is going up, on the Cisco router show IP DHCP binding.

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What you'll notice is a whole bunch of IP addresses have now been allocated, so 10.1.1.1, 10.1

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1.2, 3, 4, and it just carries on.

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Basically, Kali Linux has exhausted the DHCP pool on the Cisco router

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and as I keep scrolling, what you'll notice is all addresses have been taken from this pool.

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There are no IP addresses left in this pool show IP, DHCP, Questionmark, pool.

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Let's press enter here.

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253 addresses have been allocated from the pool, the reason why it's 253

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is the router is using IP address 10.1.1.254.

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So this IP address shouldn't be allocated to clients because that's the IP address that the router is

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using.

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So again, show IP, DHCP pool shows us that at this point we've successfully exhausted the DHCP pool

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on the DHCP server.

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No IP addresses are going to be available for the Windows 10 client when we started up.

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So I'll start that up and I'll open up a console to the Windows device.

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It'll take a while for this device to boot up, but once it's booted up fully, we'll see that it won't

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get an IP address because we've exhausted the IP addresses in the DHCP pool.

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Now, warning I will give you is a lot of packets are being sent into the network that can cause all

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kinds of issues.

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So don't run this in a production network.

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Be careful where you're going to run these attacks.

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Notice the number of DHCP, discover messages being sent into the network.

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OK, so my Windows PC is booted up, I'm going to open up a command prompt and what I'll do is make

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this bigger so the font isn't so small.

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It's running really slowly here, and that's probably because of the number of broadcasts being sent

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to the network, if I type IP config notice, no IP address has been allocated to this Windows PC.

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It's using the default 169.254 IP address range IP config slash renew.

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This device is not going to get an IP address because we've exhausted the DHCP pool on the DHCP server, but what

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we can do now is launch our second attack.

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So I'm going to click launch attack

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and let's set up a DHCP rogue server.

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IP address is going to be 10.1.1.3.

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That's the IP address of our Kali Linux server.

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I'm going to allocate IP addresses in the range 10.1.1.100 to 10.1.1.150.

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I'll set the least time to 3600 secconds.

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Same for renew subnet mask will be

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this the default router is now going to be Kali.

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It's not going to be the actual router in the network DNS server will set as Google and the domain name.

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You probably don't want to use something like hacked.com.

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Let's just specify home.com and click, OK.

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OK, back on the Windows, host type IP config notice we've been given this IP address 10.1.1

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100 and notice this default gateway is 10.1.13.

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That's really important the actual default gateway is 10.1.1.254.

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Kali Linux is using IP address 10.1.1.3.

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So IF Config more shows us that this is the IP address of the Kali Linux host, so the Windows computer

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is using Kali as its default gateway.

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That's important because when the Windows host sends traffic to the Internet, that traffic is going

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to go via Kali to this router, onto the Internet.

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So as an example, the router has this loopback interface configured on it of 1.1.1

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.1 that's essentially a loopback or imaginary interface on the router that allows us to add a

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subnet to the router. The PC at the moment, won't be able to ping that loopback address because the

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traffic is going through the network to Kali

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but Kali is not forwarding that traffic to the router.

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We need to type a command on the Kli Linux host to forward the traffic.

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So, again, notice the pings are failing.

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So in Kali,  we going to type sysctl

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-w. net ipv4 IP_forward=one.

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Basically, we're going to allow the Linux host to forward traffic that's sent to it.

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So on the Windows PC ping, 1.1.1.1 now works.

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That traffic is going via the Kali Linux server and we can see that by going to applications, sniffing

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and spoofing, 

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wireshark.

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So Wireshark will allow us to see the traffic being sent on the network.

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I'm going to capture traffic on Ethernet 0 and I'll filter this for ICMP traffic.

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So back on the Windows PC, if I ping 1.1.1.1, we can see that traffic

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from the PC to the router.

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We see a bunch of ICMP redirects, but essentially the traffic is being sent through Kali to the router.

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We only see half the conversation, but we can see the pings

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and this is the important piece.

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Let's assume the administrator of the router did something very stupid and allowed Telnet connections.

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So on the Windows PC, I'm going to telnet to the router to administer the router, we should actually

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be using SSH.

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So before I click, OK.

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Let's filt for Telnet in Wireshark

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and I'll click open in PuTTy.

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Now, that font is very small, but I'll enter the password and log in.

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So I've changed the font now, basically the router prompted for a password, which I entered and I'm

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now in what's called user mode type enable, enter my password, and I'm in privileged mode.

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But noticing Kali, now, I can see Telnet information, including the password, here's the password C

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i

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s c o, Cisco.

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Now, that's not such an easy way to view it

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so I'm going to

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right

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click on a packet and click follow TCP stream

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and what you'll notice there, there's the first password I typed enable there's the second password,

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which is Cisco.

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So I was able to see the password that was transmitted from the Windows host to the router because the

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traffic is being sent through the Kali Linux host to the router.

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So that is an example of a man in the middle attack, now on the PC

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I'll open up a Web browser

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and what I'll do in Kali

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is specify HTTP.

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So let's look at HTTP traffic.

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You should be using HTTPS, most websites use HTTPS, but again, if I connect to the router and put

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in my username and password using HTTP and sign in.

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I can log into the router and I'll be able to view information on the router, such as monitor the

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router by using command on the router.

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So I could type show IP interface brief as an example and execute that command on the router using HTTP

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But back in Cali, you'll notice I'll be able to see all the traffic from the PC to the router.

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And one of the things I want to point out here is notice authorization there, all of the credentials,

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username and password used to log into the Cisco router.

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Again, that's a man in the middle of tech, the PC sending the traffic to its default gateway, which

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is the Kali Linux host, which is sending it to the router

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but we could connect to the Internet.

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So on the Windows PC, I'll open up another tab.

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Most websites are now using encryption.

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One of them that's not which is really bad is Oxford University, oxacuk.

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That website is using HTTP not HTTPS notice it says not secure in the output here.

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Very bad.

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Your connection to the site is not secure.

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We've been told.

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So back in, Kali, we can see traffic sent from the Windows 10.1.1.100 to 129

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67. 242. 154 which is the Oxford University website now, at least here

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on their website when you try and log in.

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So go to Oxford students as an example, they are now using encryption, so only part of their website

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is in clear text we should be using HTTPS today

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but the point is, I can see part of their website through Kali Linux by using this man in the middle

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attack. 

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You should always make sure that your traffic is encrypted and that you're using a valid certificate. a

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So it's really important that you verify that the certificate is a good certificate that it's been

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issued correctly, that it's not a rogue certificate.

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So make sure that your traffic is encrypted, especially if you're using wireless hotspots or open networks,

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make sure that the certificate is valid because the traffic could be going through a device such as

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Kelly Linux.

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Don't just connect to any network.

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Make sure that networks that you connect to are good.

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Make sure that you use a VPN or some kind of encryption mechanism so that your traffic is not sent in

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clear text.