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CAPTIVE PORTALS (Part-3)

This is part-3 on wifi-cracking and in this writeup we will be discussing on CAPTIVE PORTALS networks.

Lets move directly to the CAPTIVE PORTALS this are usually the open wifi networks, widely used in hotels, airports, coffeeshops etc.They allow users to access the internet after logging in using web interface.

In general when you try to connect with this types of networks your web browser pops up the login page just like this.

There are number of ways to to bypass captive portals:

  1. Change MAC Address to one of a connected client
  2. Sniffing in monitor mode
  3. Connect and sniff login after running arp spoofing attack
  4. Create a fake AP, ask user to login

The first method is very much easy and we have discussed this in our previous writeups, just use airodump-ng to the target network see all the clients and use macchanger to change MAC Address of your wireless adapter to the same as one of the connected client easy peasy you get access but sometimes it may be suspicious because there will two device with same MAC Address on that network . So lets talk about some more methods.

Since captive portals are open and they don’t use any encryption unless data is sent over https so we can easily sniff data sent to/from it by using airodump-ng and then use Wireshark to read all data including password.

root@kali:~# ifconfig wlan0 down
root@kali:~# ifconfig wlan0 mode monitor
root@kali:~# ifconfig wlan0

NOTE: Set your wirelass card in monitor mode

root@kali:~# airodump-ng wlan0

Select the OPN network which is your target and paste bssid and channel respectively for it and use write to capture all the data in the file named KEY

root@kali:~# airodump-ng --bssid          --channel   --write KEY  wlan0

See now simply just need to deauthenticate any of the client which is conneted to that portal by

root@kali:~# aireplay-ng --deauth 10000 -a (MAC ADDRESS OF TARGET ACCESS POINT) -c (MAC ADDRESS OF MACINE TO DISCONNET) wlan0

we have discussed this attack many times even in more details so just see our previous blog posts or details deauthentication attack post in which I have explained it in depth.

And then wait for the client to once again connect with router and when clients connect to it, Simply open Wireshark and search for the file KEY.cap and use filter http because logins forms are sent over it search then for operation like login or sign in and there you will get your password.

Lets approach to some more easier technique wihich is using arp spoofing you can use the classic mitm arp spoofing technique if you know that and if you don’t see our posts on arp-spoofing for detailed info but I am going to use one of coolest tool for this attack which is ettercap

root@kali:~# ettercap -Tq -H arp:remote -i wlan0 ///

You can see details for ettercap tool in bash by help command we are using it in arp mode and we use /// to work on all the clients conneted to that network

So what happens when you run the above command all clients are disconnected from the networks and when anyone try to login to the captive portal the data will be redirected to us and all credentials will be displayed to your terminal you even don’t need to search unlike in Wireshark.

If all the above attacks are not successful than the only opting is to create fake Access point with the same name of captive portal but for these you must some basic knowledge of (html/css/js) to do exact copy of login portal and after creating a clone of the portal deauthenticate an user use your fake network with the cloned page and sniff the login credentials.

STEP 1: Cloning the login page used by the captive portals

  • Open the portal page in your respective browser
  • Press ‘alt’ for menubar go to file and select ‘save page as’ and download it in your desired location
    • generaly there will be two files one webpage(html file rename it (index.html) ) and a folder(for styling and images)
  • go to ‘var/www/html’ and paste the index.html file and folder and remove all other html file and other files also and than start your server by:
root@kali:~# service apache2 start

(If you go to your own IP Address or 127.0.0.1 the downloaded cloned login page will be displayed )

NOTE: See there are lot of different login pages examples so we cannot illustrate each and every page in general you need to make some slight changes in html/css code to bring perfection in that login page and make changes in favourite editor save it and try to make exact copy

In general for relative url in the webpage you have to add ‘/’ at the very begining of every url <link href=”/…” these things vary too much sometimes its not required

One most important thing is you also need to add form tag if its not their for this you need to right click or go to developer tools inspect or search for the input tags where user enter the credentials if you find it inside the <form> tag than it good enough and if not add it like <form method="post" action="index.html"> this and don’t forget to close the form tags.

If you are new to these things and not getting what the hell we are doing just see our EVIL TWIN post there we used a tool named ‘fluxion’ to create fake access point which do these heavy lifting for us .

You also need to manipulate login button open the index.html file in your editor either it will be in span tag or button just remove those tags and add it in see styling(css/sass) totaly depends on you how prefect you can clone it .

Now our webpage is cloned we need to create a fake AP with same you can do this with the help of mana toolkit or airbase-ng but here I am going to illustrate the manual method to create a fake AP which is faster than all of this all tools are based on this concept.

The main components of a wifi network are:

COMPONENTS TOOLS WE WILL BE USING
A router broadcasting signal Wifi card with hostapd
A DHCP server to give IP’s to client dnsmasq
A server to handle DNS request dnsmasq

STEP 2:

Lets install the

root@kali:~# apt-get install hostapd dnsmasq

after installing the tools make sure to connect your wireless card and check by ‘ifconfig’ and follow further steps.

root@kali:~# service network manager stop
root@kali:~#

Sometimes while creating the fake AP you may get an error related to iptables so we running some commands to flush it.

NOTE: We need configuration files for hostapd and dnsmasq you can get the configuration file from our Github repo just download it and keep this in folder to illustrate further attack I have kept my conf file in the folder named fake-ap (/root/Downloads/fake-ap) feel free to set your own folder name but be careful while running commands.

Before starting dnsmasq. we need you go to your downloads directory and and in the folder where we kept our ‘dnsmasq.conf’ file and customize up to your requirements and incase you don’t understand what to do in there their is an detailed explanation of .conf file inside it.

root@kali:~# dnsmasq -C /root/Downloads/fake-ap/dnsmasq.conf

Once it’s started we need to do same thing for our hostapd configuration file go to your downloads directory and the folder open ‘hostapd.conf’ file and customize the ssid parameter (set ssid name to same as captive portal you are targeting ) because when they won’t be able to connect to there original network they will try to connect to our fake AP of the same name so after setting the config file start it by

root@kali:~# dnsmasq -C /root/Downloads/fake-ap/hostapd.conf -B

(-B FOR BACKGROUND EXECUTION)

root@kali:~# ifconfig

Check wether you got the new ip address and netmask according to hostapd.conf If yes feel free to move ahead and if not run the below commands:

root@kali:~# ifconfig wlan0 (Ip ADDRESS as give inhostapd.conf file)  netmask 255.255.255.0 (bydefault its same for all)

e.g

root@kali:~# ifconfig wlan0 10.0.2.1  netmask 255.255.255.0

Start your cloned we login page for

root@kali:~# service apache2 start

Now if you see all wifi networks your fake AP will be their with other networks it will work fine if you try to connect it and when you start web surfing it will ask to login first, Yes we got our fake AP running smoothly but still it will refuse to load and also request are sent by different systems (depends on OS) are not handled properly in order to fix this all we first need to redirect all requests starting with ‘www’ to be handled only by its domain for example “www.yahoo.com” > “yahoo.com” for this we need to set some rule in our server configuration file in order to open that :

root@kali:~# leafpad /etc/apache2/sites-enabled/000-default.conf

this will be open in order to add some rules first add as shown in below image:

Now to handel(404) error page for all systems (Except ios device ) add rule at top as shown in image:

In order to handel error for ios device write the below rules shown in image you can find all these rules in our Github repo.

Restart your server

root@kali:~# service apache2 restart

Now our fake AP can handel all requests and error from different the only problem we left out is sites which uses https we also need to add https to our own server, so we are going to generate a fake SSL certificate by:

root@kali:~# openssl req -new -x509 -day 365 -out /root/Downloads/fake-ap/cert.pem -keyout /root/Downloads/fake-ap/cert.key

BREAKDOWN (for above command):

openssl: use to create ssl certificate -new : for network -x509: general used structure for certificate 365: valid for 1 year

Saving the certficate in root/Downloads/fake-ap/cert.pem and key in -keyout /root/Downloads/fake-ap/cert.key

After hitting enter it will ask for key (set as you desire)and some general ques to generate certficate like (country, locality, domain ….etc >name) after all this certficate will be generated at your given location after this enable ssl by

root@kali:~#  a2enmod ssl

Once again open :

root@kali:~# leafpad /etc/apache2/sites-enabled/000-default.conf

If you notice <Virtualhost 80> is running for http and to enable ssl just add one more tag as shown in image:

root@kali:~# leafpad /etc/apache2/ports.conf

TO add port for ssl sometimes it’s already writen there :

thats all ! Restart server once again with all lopehole covered ready to handle all https and http request also with error(404) pages to :

root@kali:~# service apache2 restart

Now we covered each loopholes for our fake AP run the final step.

STEP 3:

Run a deauthentication attack on any client on that network for a long time so when user is unable to connect to the original network he will try connect to our fake AP and for that we will sniffing the data using Wireshark.

root@kali:~# tshark -i wlan0 -w key.cap

(we are writing our captured data in the file named key.cap) and when user connects to our fake AP by there login credentials we get the username and password for this you just open the ‘key.cap’ file in wireshark use filter ‘http’ inside that search for post request inside that you will get credentials.

I know this process is quite long and little bit difficult to understand, Yes we can use any specific tool which do all this heavy liftings for us but the purpose behind this post was to make you aware on the core concept of fake ACCESS POINT and all those tools are also built on this concept only, and by using the concept of fake access point cracking of WPA Enterprise become easy.

You can get all the neccessary resources from our Github repository, and see WPA Enterprise cracking part.

I hope you enjoyed this writeup and learnt something new if you have any queries feel free to ask in comments box or contact us through mail, or have suggestions for improvements ? We’d love to hear you, send us an email!