how to accomplish a brute force attack

This article is designed to demonstrate how to accomplish a brute force attack, and what it looks like from the receiving end. Brute force means password guessing. This can only feasibly be accomplished with the aid of good target reconnaissance and some automated programs. While it is very easy to write your own brute force program, there are several available for free online. I find Brutus to be one of the best brute force tools. You can find it at Hoobie.net.

The first step in a brute force attack (or for that matter, any attack) is target enumeration. This is the process by which we find where and how a target is vulnerable. I use NMAP for almost all of my initial cursory scans of networks. Lets use the target of my own desktop server and run an NMAP scan to find out what we have to play with. The output from my scan follows:

nmap -sS -O 216.25.200.135

Starting nmap V. 2.30BETA17 by fyodor@insecure.org (
http://www.insecure.org/nmap/ )
Interesting ports on ip-216-25-200-135.covad.dsl.fcc.net
(216.25.200.135):
Port State Service
21/tcp open ftp
25/tcp open smtp
80/tcp open http
135/tcp open loc-srv
139/tcp open netbios-ssn
443/tcp open https
445/tcp open microsoft-ds
1025/tcp open listen
1026/tcp open nterm
1031/tcp open iad2

TCP Sequence Prediction: Class=random positive increments
Difficulty=7635 (Worthy challenge)
Remote operating system guess: Windows 2000 RC1 through final release

Nmap run completed -- 1 IP address (1 host up) scanned in 1 second

Ok, so we’ve got several services to choose from on this target. The first one that catches my eye is FTP. We can use this to brute force passwords, and we can use smtp to check for user accounts. Now the fun begins. I’ll first try ftp to find if anonymous ftp is enabled (which could potentially make my task a lot easier, there are rare computers with completely open upload/download ftp servers without strong restrictions (allowing you to upload and download to the web root folder)).

C:\>ftp 216.25.200.135
Connected to 216.25.200.135.
220 WIN2KSERVER Microsoft FTP Service (Version 5.0).
User (216.25.200.135:(none)): anonymous
331 Password required for anonymous.
Password:foo@nowhere.com
530 User anonymous cannot log in.
Login failed.
ftp> quit
221 Fuck off!

It seems that anonymous ftp isn’t enabled, and not only that the server is quite rude when I leave. The server did give some confirmation that it is running Windows NT, or in this case Windows 2000 (dead giveaway in the machine’s name ‘WIN2KSERVER’). We’ll try the SMTP server now to check for user names.

220 WIN2KSERVER Microsoft ESMTP MAIL Service, Version: 5.0.2195.2966
ready at Fri, 22 Jun 2001 09:08:49 –0400
vrfy smellydell
252 2.1.5 Cannot VRFY user, but will take message for smellydell
vrfy administrator
252 2.1.5 Cannot VRFY user, but will take message for administrator

well, there’s no use in verifying anyone on this server as it seems that the server will give the same message for real and bogus accounts (all NT servers have an ‘administrator’ account, in much the same way that *nix have root accounts). The ‘expn’ command didn’t work at all on this server (replied with ‘unknown command’ at expn postmaster). So at this point I’m S.O.L., but some machines will give a very good list of users and or active accounts using the smtp server.

Ok, so I’m off to brute forcing. The first thing I do is fire up Brutus.

Screenshot of brutus at startup

Next I’ll have to modify my users list (found in users.txt in the Brutus directory) to include users I suspect to be on an NT server. NT always has a ‘Guest’ account and an ‘Administrator’ account. I’ll add a few more guesses. In the end my users list looks like this:

A text file list of users

The next step is to fire Brutus at the target, when configured for an ftp attack, Brutus appears thus:

Configuring brutus

You’ll notice I set the timeout higher than the default. Brutus nicely circumvents connection limits by creating new connections for every request. This is useful because some servers will cut your connection after 3 bad guesses at passwords. Brutus uses the targets ability to take multiple ftp requests and creates a new request for every guess (I have set the program to make 10 requests simultaneously). The timeout is the lag time that the program will allow before it makes a new request. If you don’t set this high enough you are likely to flood the target and either crash its server, or simply hang Brutus. You can use a really high connection and low timeout rate as an effective DoS attack that will knock weak servers completely off the net.

So now I’ll fire Brutus at the target. I’m using the default password list that comes with the program, but there are several larger, and more complete word lists available online. What Brutus will do is try every username listed in the users file with every password in the word list (and can even generate its own random word list to include all combinations of letters, characters, and numbers). Remember that most passwords are 8 characters long, so its usually not worthwhile to try and brute force very short passwords. Here’s what Brutus looks like in action:

Screenshot of brutus attacking a target

Now, the downside to brute forcing is that it is extremely noisy, and even the worst sysadmin should notice it. During my demonstration my server immediately popped an alert that the system log was full. A quick examination of the system log reveals the problem immediately:

Screenshot of an NT event log

All those warnings you see are bad FTP login attempts. A double click on the alert shows:

Screenshot of an event log detail showing the brute force attack

It isn’t hard to figure out exactly what is going on. Even more disturbing is the log file left behind. Here’s a snippit:

13:30:18 216.25.200.135 [5]USER admin 331
13:30:18 216.25.200.135 [6]USER admin 331
13:30:18 216.25.200.135 [7]USER admin 331
13:30:18 216.25.200.135 [8]USER admin 331
13:30:18 216.25.200.135 [9]USER admin 331
13:30:18 216.25.200.135 [10]USER admin 331
13:30:18 216.25.200.135 [11]USER admin 331
13:30:18 216.25.200.135 [12]USER admin 331
13:30:18 216.25.200.135 [13]USER admin 331
13:30:18 216.25.200.135 [4]PASS - 530
13:30:18 216.25.200.135 [14]USER admin 331
13:30:18 216.25.200.135 [5]PASS - 530
13:30:18 216.25.200.135 [6]PASS - 530
13:30:18 216.25.200.135 [7]PASS - 530
13:30:18 216.25.200.135 [8]PASS - 530
13:30:18 216.25.200.135 [9]PASS - 530
13:30:18 216.25.200.135 [10]PASS - 530
13:30:18 216.25.200.135 [11]PASS - 530
13:30:18 216.25.200.135 [15]USER admin 331
13:30:18 216.25.200.135 [16]USER admin 331

Not only do you notice all the tries for the same account, but you can tell it is an automated attempt to brute force because the times of the attempts are so close together (60 or so attempts a second). Even more damning is that my IP address is logged all over the huge log file. Its not hard to spot me or figure out what I’m attempting to do. Be warned if you attempt a brute force that you are probably going to get notice.

Now, I happened to be successful on this attempt and got on username and password. The results are displayed in Brutus under the ‘Positive Authentication Results’ window:

Screenshot showing brutus successfully identifying login information

You can see the username ‘user’ and password ‘charles’ worked on the server. Lets try them out:

C:\>ftp 216.25.200.135
Connected to 216.25.200.135.
220 WIN2KSERVER Microsoft FTP Service (Version 5.0).
User (216.25.200.135:(none)): user
331 Password required for user.
Password: charles
230-Fuck you!
230 User user logged in.
ftp>

Boom, and its just that easy. Now that I’m in my first step should be to attempt to clean up the traces of my attack (i.e. the log files and system event logs). Accomplishing this task takes more explanation than I have time for here, but hopefully you get the idea.

If nothing else, this short article should show you the value of good passwords. If I hadn’t set up the account ‘user’ with such a crappy password this attack most likely would have been unsuccessful. See my article on passwords for a good run down of how to pick a good password to keep your accounts safe from brute force attempts.

Tutorial: How to hack with a ip address

Tutorial: How to hack with a ip address

So say somehow somewhere we ended up choosing a target to start wreaking havoc upon. All we need is an IP Address. Theres plenty of papers out there that go into how to obtain an IP Address from the preferred mark of your choice. So I'm not going to go into that subject. Alright so say we got the targets IP Address finally. What do we do with this IP Address. Well first ping the IP Address to make sure that its alive. In otherwords online. Now at the bottom of this document ill include some links where you can obtain some key tools that may help on your journey through the electronic jungle. So we need to find places to get inside of the computer so we can start trying to find a way to "hack" the box. Port Scanners are used to identify the open ports on a machine thats running on a network, whether its a router, or a desktop computer, they will all have ports. Protocols use these ports to communicate with other services and resources on the network.

1) Blues Port Scanner - This program will scan the IP address that you chose and identify open ports that are on the target box.

Example 1:
Idlescan using Zombie (192.150.13.111:80); Class: Incremental
Interesting ports on 208.225.90.120:
(The 65522 ports scanned but not shown below are in state: closed)
Port State Service
21/tcp open ftp
25/tcp open smtp
80/tcp open http
111/tcp open sunrpc
135/tcp open loc-srv
443/tcp open https 1027/tcp open IIS
1030/tcp open iad1
2306/tcp open unknown
5631/tcp open pcanywheredata
7937/tcp open unknown
7938/tcp open unknown
36890/tcp open unknown


In example 1 now we see that there are a variety of ports open on this box. Take note of all the ports that you see listed before you. Most of them will be paired up with the type of protocol that uses that port (IE. 80-HTTP 25-SMTP Etc Etc...) Simply take all that information and paste it into notepad or the editor of your choice. This is the beginning of your targets record. So now we know what ports are open. These are all theoretical points of entry where we could wiggle into the computer system. But we all know its not that easy. Alright so we dont even know what type of software or what operating system that this system is running.

2) NMAP - Port Scanner - Has unique OS fingerprinting methods so when the program sees a certain series of ports open it uses its best judgement to guess what operating system its running. Generally correct with my experiences.

So we have to figure out what type of software this box is running if we are gonna start hacking the thing right? Many of you have used TELNET for your MUDS and MOOS and weird multiplayer text dungeons and many of you havent even heard of it before period. TELNET is used to open a remote connection to an IP Address through a Port. So what that means is we are accessing their computer from across the internet, all we need is their IP Address and a port number. With that record you are starting to compile, open a TELNET connection to the IP Address and enter one of the OPEN ports that you found on the target.
So say we typed 'TELNET -o xxx.xxx.xxx.xxx 25' This command will open up a connection through port 25 to the IP xxx.xxx.xxx.xxx. Now you may see some text at the very top of the screen. You may think, well what the hell, how is that little string of text going to help me. Well get that list you are starting to write, and copy the banners into your compilation of the information youve gathered on your target. Banners/Headers are what you get when you TELNET to the open ports. Heres an example of a banner from port 25.


220 jesus.gha.chartermi.net ESMTP Sendmail 8.12.8/8.12.8; Fri, 7 Oct 2005 01:22:29 -0400


Now this is a very important part in the enumeration process. You notice it says 'Sendmail 8.12.8/8.12.8' Well what do ya know, we now have discovered a version number. This is where we can start identifying the programs running on the machine. There are some instances in which companies will try and falsify their headers/banners so hackers are unable to find out what programs are truly installed. Now just copy all the banners from all the open ports *Some Ports May Have No Bannners* and organize them in the little record we have of the target. Now we have all the open ports, and a list of the programs running and their version numbers. This is some of the most sensitive information you can come across in the networking world. Other points of interest may be the DNS server, that contains lots of information and if you are able to manipulate it than you can pretend to hotmail, and steal a bunch of peoples email. Well now back to the task at handu. Apart from actual company secrets and secret configurations of the network hardware, you got some good juicy info. http://www.securityfocus.com is a very good resource for looking up software vulnerabilities. If you cant find any vulnerabilities there, search on google. There are many, many, many other sites that post vulnerabilities that their groups find and their affiliates.

At SecurityFocus you can search through vendor and whatnot to try and find your peice of software, or you can use the search box. When i searched SecurityFocus i found a paper on how Sendmail 8.12.8 had a buffer overflow. There was proof of concept code where they wrote the shellcode and everything, so if you ran the code with the right syntax, a command prompt would just spawn. You should notice a (#) on the line where your code is being typed. That pound symbol means that the command prompt window thats currently open was opened as root. The highest privilage on a UNIX/Linux Box. You have just successfully hacked a box. Now that you have a command shell in front of you, you can start doing whatever you want, delete everything if you want to be a fucking jerk, however I dont recommend that. Maybe leave a text file saying how you did it and that they should patch their system.....whoever they are. And many times the best thing you can do is just lay in the shadows, dont let anyone know what you did. More often than not this is the path you are going to want to take to avoid unwanted visits by the authorities.

There are many types of exploits out there, some are Denial of Service exploits, where you shut down a box, or render an application/process unusable. Called denial of service simply because you are denying a service on someones box to everyone trying to access it. Buffer Overflow exploits are involved when a variable inside some code doesnt have any input validation. Each letter you enter in for the string variable will be 1 byte long. Now where the variables are located at when they are in use by a program is called the buffer. Now what do you think overflowing the buffer means. We overflow the buffer so we can get to a totally different memory address. Then people write whats called shellcode in hex. This shellcode is what returns that command prompt when you run the exploit. That wasnt the best description of a buffer overflow, however all you need to remember is that garbage data fills up the data registers so then the buffer overflows and allows for remote execution of almost every command available. There are many, many other types of attacks that cannot all be described here, like man-in-the-middle attacks where you spoof who you are. Performed correctly, the victim will enter http://www.bank.com and his connection will be redirected to your site where you can make a username and password box, make the site look legit. And your poor mark will enter their credentials into your site, when they think its really http://www.bank.com. You need to have a small script set up so it will automatiically display like an error or something once they try and log in with their credentials. This makes it seem like the site is down and the victim doenst give it a second thought and will simply try again later.
__________________________________________________ _______o_________

So as a summary of how to 0Wn a box when you only have an IP Address
Method Works On BOTH *Nix and Windoze

****You can do the same with domain names (IE google.com) than what you can with IP Addresses. Run a WHOIS Lookup or something along those lines. Or check up on InterNIC you should be able to resolve the domain name to an IP address.****

- Port Scan The Address And Record Open Ports
- Telnet To Open Ports To Identify Software Running On Ports

3) netcat - Network swiss army knife. Like TELNET only better and with a lot more functionality. Both can be used when you are trying to fingerprint software on open ports

- Record Banners And Take Note Of The Application Running and The Version Number
- Take A Gander Online At SecurityFocus.com or Eeye.com. If you cant find any vulnerabilities then search google.
- Make a copy of some Proof-Of-Concept code for the vulnerability.

*Read the documentation if there is any, for the proof-of-concept code you will be using for your exploit*

- Run The Exploit Against The Victim.
- Reap The Cheap-Sh0t Ownage
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**This document does not go into covering your tracks. If you dare try any of this stuff on a box you dont have consent to hack on, They will simply look at the logs and see your IP Address and then go straight to your ISP. Once you get more 1337 you get to learn how to get away with the nasty deeds. This is what the majority of kode-kiddies do when they perform attacks. The key is to enumerate all the info you can from the machine, the more info you have on the system the better. User accounts can also be enumerated. Once you have a list of account names, you may then proceed to brute-force or perform a cryptanalysis attack to gain control of the account. Then you must work on privilage escalation. Users are not Admins/Root**