Setup a Fake Access Point With BackTrack5

Recently I needed to setup a fake access point for a presentation, I fired up my Backtrack5 VM, Connected my Alfa AWUS036H USB adapter and started to configure the Fake AP.

There are a lot of Tutorials and Scripts for setting up a Fake AP,  The “Gerix”  tool also have an option to auto set a Fake AP (for some reason this tool never worked for me).

I started to setup my fake AP and had run into some trouble for a strange reason.

I decided to put my experience here hopefully you’ll find it useful.

Started by putting my Wlan interface in monitor mode

root@Blackbox:~/fakeap# airmon-ng start wlan1
Found 1 processes that could cause trouble.
If airodump-ng, aireplay-ng or airtun-ng stops working after
a short period of time, you may want to kill (some of) them!
PID     Name
1558    dhclient
Interface       Chipset         Driver
wlan1           Realtek RTL8187L        rtl8187 - [phy1]SIOCSIFFLAGS: Unknown error 132
                                (monitor mode enabled on mon0)

I noticed the following error: “Unknown error 132″
Tried using airodump-ng to see what happens…

root@Blackbox:~/fakeap# airodump-ng mon0
ioctl(SIOCSIFFLAGS) failed: Unknown error 132

Got the same error.

The solution was simply to unload the RTL8187 and Load the R8187 driver instead as follows:

root@Blackbox:~/fakeap# rmmod rtl8187
root@Blackbox:~/fakeap# modprobe r8187

Tried putting wlan In monitor mode again

root@Blackbox:~/fakeap# airmon-ng start wlan1
Found 1 processes that could cause trouble.
If airodump-ng, aireplay-ng or airtun-ng stops working after
a short period of time, you may want to kill (some of) them!
PID     Name
1558    dhclient
Interface       Chipset         Driver
wlan1           RTL8187         r8187 (monitor mode enabled)

Well, that fixed the problem

root@Blackbox:~/fakeap# iwconfig
lo        no wireless extensions.
eth3      no wireless extensions.
wlan1     802.11b/g  Mode:Monitor  Channel=10  Bit Rate=11 Mb/s
          Tx-Power=5 dBm
          Retry:on   Fragment thr:off
          Link Quality=0/100  Signal level=50 dBm  Noise level=-156 dBm
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

Now we can proceed to the fake ap setup process

1. Install a DHCP Server

apt-get install dhcp3-server

2. Edit “/etc/dhcp3/dhcpd.conf” as follows (You can change ip address, pool and dns server as needed):

ddns-update-style ad-hoc;
default-lease-time 600;
max-lease-time 7200;
authoritative;
subnet 10.0.0.0 netmask 255.255.255.0 {
option subnet-mask 255.255.255.0;
option broadcast-address 10.0.0.255;
option routers 10.0.0.254;
option domain-name-servers 8.8.8.8;
range 10.0.0.1 10.0.0.140;
}

3. Put your wlan in monitor mode

airmon-ng start wlan1

4. Start airbase-ng, you will need to specify the AP SSID and channel number

airbase-ng -e FreeWifi -c 11 -v wlan1 &

5. Airbase will create a new adapter “at0″ you will need to enable it and assign it with an ip address and subnet mask, the ip address you assign to this interface will be the default gateway that you specified in the dhcpd.conf file.

ifconfig at0 up
ifconfig at0 10.0.0.254 netmask 255.255.255.0

6. Add a route

route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.0.0.254

7. Setup ip tables

iptables --flush
iptables --table nat --flush
iptables --delete-chain
iptables --table nat --delete-chain
iptables -P FORWARD ACCEPT

• Eth3 is my external interface which is connected to the internet change it to whatever yours is

iptables -t nat -A POSTROUTING -o eth3 -j MASQUERADE

8. Clear dhcp leases

echo > '/var/lib/dhcp3/dhcpd.leases'

9. Create a symlink to dhcpd.pid (skipping this may cause an error when starting dhcp server)

ln -s /var/run/dhcp3-server/dhcpd.pid /var/run/dhcpd.pid

10. Start the DHCP server

dhcpd3 -d -f -cf /etc/dhcp3/dhcpd.conf at0 &

11. Don’t forget to enable IP forwarding

echo "1" > /proc/sys/net/ipv4/ip_forward

That’s All Folks!

I have created a simple bash script to automate this process you will just need to change it  to suit your configuration.

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#!/bin/bash

echo "Killing Airbase-ng..."
pkill airbase-ng
sleep 2;
echo "Killing DHCP..."
pkill dhcpd3
sleep 5;

echo "Putting Wlan In Monitor Mode..."
airmon-ng stop wlan1 # Change to your wlan interface
sleep 5;
airmon-ng start wlan1 # Change to your wlan interface
sleep 5;
echo "Starting Fake AP..."
airbase-ng -e FreeWifi -c 11 -v wlan1 & # Change essid, channel and interface
sleep 5;

ifconfig at0 up
ifconfig at0 10.0.0.254 netmask 255.255.255.0 # Change IP addresses as configured in your dhcpd.conf
route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.0.0.254

sleep 5;

iptables --flush
iptables --table nat --flush
iptables --delete-chain
iptables --table nat --delete-chain
iptables -P FORWARD ACCEPT
iptables -t nat -A POSTROUTING -o eth3 -j MASQUERADE # Change eth3 to your internet facing interface

echo > '/var/lib/dhcp3/dhcpd.leases'
ln -s /var/run/dhcp3-server/dhcpd.pid /var/run/dhcpd.pid
dhcpd3 -d -f -cf /etc/dhcp3/dhcpd.conf at0 &

sleep 5;
echo "1" > /proc/sys/net/ipv4/ip_forward

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4 Comments

  1. [...] my previous post I discussed how to Setup a Fake Access Point with Backtrack [...]


  2. Brad
    Dec 30, 2011

    Thank you for this tutorial! I referred to this so much as I learned how to create a man-in-the-middle set-up. And your script worked perfectly… after I corrected the incorrect way it pasted. I am new to Linux and trying to learn. I am using Backtrack5r1 on a VirtualBox on an MacBookPro running Lion.


  3. John
    Jan 20, 2012

    hi
    i get it all running , the dhcp is working and assigning ip’s , BUT when clients connect to the fake AP the connection is very slow, ive tested using eth0 as internet and my connection on eth0 is like 24mb, when a client is connected to the fake AP they can barely surf ?

  4. [...] up a fake AP with BT5 and my good old loved ALFA . There’s a whole bunch of scripts out there which do the job nicely, if you are ready to modify them here and [...]

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