Archives

All posts for the month July, 2017

Password cracking plays a very important role in hacking. We are not always lucky to get credentials during enumeration. There are two types of password cracking.

  1. Online password cracking
  2. Offline password cracking

In this tutorial we will learn about online password cracking. There are many techniques used in online password cracking. Some of them are,

Dictionary Attack: Dictionary password attack is a password cracking attack where each word in a dictionary (or a file having a lot of words) is tried as password until access is gained. This method will be successful when simple passwords are set. By simple, I mean common passwords which can be found in a dictionary like password, iloveyou etc. This type of attack consumes less time but is not bound to be successful always especially if the password is not present in the dictionary.

Brute force Attack: Brute Force attack is a password cracking attack similar to dictionary attack. The only differ ence is in this attack, each and every possible combination is tried until the password is successfully cracked. For example, if there are two words say “abc” and “123” in a wordlist, other combinations like “abc1”, “abc2” and “abc3” a re also tried. Brute force attack will definitely succeed even if it means it will take years to do that.

Hybrid Attack: As the name suggests, it uses a combination of both dictionary and brute force password attacks to crack the password.

Rainbow Table Attack: Rainbow Table password cracking technique uses pre -computed hashes to crack the encrypted hashes.

Kali Linux has various tools in its arsenal for both online and offline password cracking. Some of the online password cracking tools are Acccheck, John The Ripper, Hydra and Medusa etc.

We have already seen the working of the tool Accheck during SMB enumeration. In this tutorial, we will see how to crack passwords with a tool called Hydra. THC-Hydra is a password cracker which uses brute forcing to crack the passwords of remote authentication services. It can perform rapid dictionary attacks against more than 50 protocols, including telnet, ftp, http, https, smb , several databases and much more.

On our target Metasploitable2, we have many services which allow remote authentication like telnet, ftp and SSH. We also have rlogin available. We will use Hydra on one of these services. Hydra can be accessed from the applications menu of Kali Linux. It is available both in GUI and command line utility. For this tutorial, I’m using the graphical one.

Once opened, Hydra will look like shown below.

Change the target IP to that of Metasploitable’ s IP.There are many protocols to choose from Here I am choosing ftp. Change the port to 21 as ftp is running on port 21. I selected options “Be Verbose” and “show attampts” to see the cracking process.

Click on “passwords” tab. We can give a single username and password or a file containing a number of usernames and passwords. Here I am giving the same dictionary or wordlist for both username and password. This dictionary is big.txt. I selected the options “Try Login as password” , “Try empty password” and “Try reverse login”. These options are self explanatory.

The tuning tab is used to configure proxy and number of simultaneous tries. I left it as default.

I left even “specific” tab to default. When all the settings are set, go to “Start” tab. To start the attack, click on “Start” button.

The attack is displayed as shown below.

The time of the attack depends on the number of words present in the dictionary or the wordlist we specified. The password is cracked if the phrase is present in the dictionary. If the password is not there in the wordlist, we need to use another dictionary. The big.txt dictionary I used failed to crack the password. So I used another wordlist we made during enumeration “pass.txt”. After some time, Hydra found three valid passwords.

Scroll up to see what are those passwords.

Apart from Hydra, Kali Linux also has command line tools to use for password cracking. One such tool is Medusa. Open a terminal and type medusa to see the options of that tool. Below is the command in medusa to crack ftp using a wordlist.

Once medusa cracks a password, it will be sh own as below. Once again we got three credentials we found also with Hydra.

We have used the same dictionary in both methods, but where do we find this dictionary or wordlist. Most wordlists of Kali Linux are present in /usr/share directory. Given below are different dictionaries in the “wordlists” folder.

These wordlists are named accordingly. For example, “common.txt” contains most common passwords used by users. But what if none of the dictionaries are helpless in cracking the password. Kali Linux also has tools to create our own dictionary or wordlist. Crunch is one such tool. The syntax is given below.

Here’s an example of how to create a wordlist with crunch.

We can also save the wordlist to a  file as shown below.

 

We have performed two types of enumeration till now. Before we perform further enumeration, let us see whether these credentials we acquired can help us in gaining access to the remote system. When we performed a scan with Nmap during scanning and enumeration stage, we have seen that ports 21,22,23 are open and running FTP, Telnet and SSH services respectively.

FTP

FTP stands for File Transfer Protocol. As the name implies, it is used to share or transfer files. This service runs on port 21 by default. Although not quite popular now, it was the most popular way of sharing files in yesteryears. It was quite popular as torrents now, only that FTP is a client-server architecture. Since FTP is used for sharing files, it has a option to enable anonymous downloads. Anonymous download is a type of download where anyone can download the file by logging in with the username of “anonymous” and password as anything. But it a was courtesy to give your email address as password in those days. Enabling anonymous account on FTP server is considered a high security risk especially if the account given not only read but also write permissions. Another disadvantage with FTP is that it uses clear text authentication. So if any hacker is sniffing on your LAN, he can see the username and password in plain text. Ok, Since our target is running FTP service, let us first check if anonymous account is enabled on the server.We can connect to FTP server through terminal by using commad “ftp target address” as shown below.

I try to login with the anonymous account with anonymous as the password and the login is successful. Good, anonymous account is enabled on the target. It’s time to check the permissions given to anonymous user.

I type command “pwd” to see the current ftp directory. It’s root directory. Next I use “put” command to upload a random file to the FTP server. As you can see in the above image, file could not be created. So anonymous account has only “read” permissions. Enabling write permissions to the anonymous account may result in propagation of malware, pirated software etc. So anonymous account is secure in this case. Next I decided to try the credentials I got during enumeration. I decided to try with “msfadmin” first. Login successful. I first checked the contents of the ftp directory. It seems this account has admin rights on the FTP server.

I once again try to upload the “shell.php” into the FTP directory. This time it’s successful.

Now I can upload any malicious file to the server and can use it for any nefarious purpose. or propagation.

TELNET

Telnet is a network protocol used to remotely administer a system. It is bi-directional and interactive communication protocol.Using telnet we can remotely communicate with a system far away. It runs on port 23. We can coonect to a telnet server from terminal just as we connected to a FTP server using command “telnet IP address”. Anyone who successfully logs into telnet will get a shell on the remote system. When I connected to the telnet server of our target system, I didn’t even need any enumeration as the username and password were displayed in the banner.

When I logged in with the credentials msfadmin/msfadmin, as you can see in the below image, I got a normal shell.

Although getting a shell on a remote system is good, we can perform limited operations with this type of shells. But don’t worry, we can get a meterpreter session on the remote system with the help of Metasploit, of course by exploiting telnet.

Start Metasploit and load the telnet module as shown below. Set all the options we need and execute the module by typing command “run”.

You can see that we successfully got a shell just like before. Type command “sessions” to display the sessions we have.

Metasploit provides a wonderful option to upgrade a command shell to meterpreter shell. Load the following post module and the set the session id as that of telnet shell. Run the module.

As you can see in the above image, we successfully got a meterpreter session on the metasploitable system. We can see all the sessions we have using command “sessions”.

We can interact with the session we want by using command “sessions -i id” where id is the session id number. We will see more about meterpreter in our later issues. For the first time, we gained access to the metasploitable system, although with limited privileges.

SSH

SSH stands for a secure shell. It was designed as a replacement for telnet and intended to be secure unlike telnet. SSH is a cryptographic network protocol which encrypts the data during remote communication. Thus it provides security and authentication also takes in encrypted format. Thus even if any hacker is sniffing on the local LAN, he still can’t any SSh credentials. SSH by default runs on port 22. Just like it has a telnet module, Metasploit also has a SSH login module. We will use the same credentials msfadmin/msfadmin to login. Load the SSH login module as shown below and configure required options.

Once all the options are set, run the module as shown below.

We have a successful login. Same as above, we can use “sessions” command to view the available sessions. We can also upgrade this SSH shell to meterpreter just as we did in the case of telnet. That was about how to hack telnet, ftp and SSH.

What We Achieved:

Using the details we gathered during enumeration, we have hacked some serrvices on the Metasploitable system. We have also gained shell and meterpreter session on the system.

 

Kali Linux is the most popular and also my favorite pen testing distro. Its regular updates and stability accord it the top spot. Apart from Kali Linux, there are many other pen testing distros available. One of them is Parrot Security distro. Parrot Security sports many more tools than Kali Linux which includes software for cryptography,cloud, anonymity, digital forensics and of course programming. One of our readers has requested us to make a guide on how to install Parrot Security OS in Vmware. So be it.

Download the Parrot Security OS . Unlike the makers of Kali Linux, Parrot Security have not yet provided a Vmware image to download. So we have to download a iso image (depending on your architecture yo- u can download a 32bit or 64 bit iso file). Once the download is finished, open Vm- ware Workstation (Version 12 used for this article). Hit “CTRL+N”. The below window should open.

Make sure the “Typical” option is selected, and click on “Next”. That takes us to the next window. Initially, the “installer disc image file” field should be empty. Click on “browse” and browse to location of the iso file we just downloaded and select it. Now the window should look like below. Click on “Next”.

The Guest operating system should be automatically selected for you, if not select Linux as OS and version as Debian 8.x (since I am installing a 32bit, make it Debian 8.x64 if installin -g 64bit). Click on Next.

Choose the name of virtual machine and its location as you like. I named it Parrot. Click on “Next”.

Allocate the hard disk memory for your virtual machine. Keep the minimum as 20GB. Click on Finish.

It will show you a summary of all the selections you made. If you want to make any changes, click on Customize hardware or else click on Next.

The virtual machine is created with the name you gave it. Power on the virtual machine. It will boot and take you to the interface shown be low.

Choose the “Install” option. In the next window select “Standard Installer”. You can select these options using “tab” button.

Select the language in which you want to continue the installation process.

Select your country. For this article, I chose location as India.

Select the keyboard configuration you want.

It is important to set the root password (no need to tell it is Linux’s most powerful account) for the machine before we do anything. Set a complex password. Read the suggestions before you set the root password.

Re-enter the root password again to confirm it.

It is a good practice to use the system as a no -n root user. The system will prompt you to create a new user account for non-administrative activities. I am creating a user with name kalyan. I am giving the same name as username.

Create a password for the user account you just created. Make it a good password for security reasons.

Re-type the password again to confirm the password you have assigned.

The next step is partitioning the hard disk. Unless you are an expert or want to try something different, use the entire disk.

The system will warn you before partitioning. Select the disk for partitioning.

It will ask you to choose the partitioning scheme. Choose the first one. It is also recommended for users.

Next, it will show you changes you have configured before writing the changes to the disk. Select “Finish partitioning and write changes to the disk”.

Confirm for one last time that you want to writ-e changes to the disk. Select “Yes”.

The installation process will start and may take some time. You can have snacks and come back. After installation finishes, it will prompt whether you want to install GRUB boot loader.

Select Yes. Then it will ask you where to install the boot loader. Select the /dev/sda disk.

After the installation is finished, it will show you a message as shown below. It’s time to boot into your new system.

As the system boots, it will ask present you a login screen. You can login as either root or the new user you created it. Once you login,your new pen testing distro should look as below.