How To Crack A Password

What is Password Cracking?

Password cracking is the process of attempting to gain Unauthorized access to restricted systems using common passwords or algorithms that guess passwords. In other words, it's an art of obtaining the correct password that gives access to a system protected by an authentication method.

Password cracking employs a number of techniques to achieve its goals. The cracking process can involve either comparing stored passwords against word list or use algorithms to generate passwords that match

In this Tutorial, we will introduce you to the common password cracking techniques and the countermeasures you can implement to protect systems against such attacks.

Topics covered in this tutorial

• What is password strength?
• Password cracking techniques
• Password Cracking Tools
• Password Cracking Counter Measures
• Hacking Assignment: Hack Now!

What is password strength?

Password strength is the measure of a password's efficiency to resist password cracking attacks. The strength of a password is determined by;

• Length: the number of characters the password contains.
• Complexity: does it use a combination of letters, numbers, and symbol?
• Unpredictability: is it something that can be guessed easily by an attacker?

Let's now look at a practical example. We will use three passwords namely

1.  password

2.  password1

3.  #password1$

 For this example, we will use the password strength indicator of Cpanel when creating passwords. The images below show the password strengths of each of the above-listed passwords.

Note: the password used is password the strength is 1, and it's very weak.

Note: the password used is password1 the strength is 28, and it's still weak.

Note: The password used is #password1$ the strength is 60 and it's strong.

The higher the strength number, better the password.

Let's suppose that we have to store our above passwords using md5 encryption. We will use an online md5 hash generator to convert our passwords into md5 hashes.

 The table below shows the password hashes

Password	MD5 Hash	Cpanel Strength Indicator
password	5f4dcc3b5aa765d61d8327deb882cf99	1
password1	7c6a180b36896a0a8c02787eeafb0e4c	28
#password1$	29e08fb7103c327d68327f23d8d9256c	60

 We will now use http://www.md5this.com/ to crack the above hashes. The images below show the password cracking results for the above passwords.

As you can see from the above results, we managed to crack the first and second passwords that had lower strength numbers. We didn't manage to crack the third password which was longer, complex and unpredictable. It had a higher strength number.

Password cracking techniques

There are a number of techniques that can be used to crack passwords. We will describe the most commonly used ones below;

• Dictionary attack– This method involves the use of a wordlist to compare against user passwords.
• Brute force attack– This method is similar to the dictionary attack. Brute force attacks use algorithms that combine alpha-numeric characters and symbols to come up with passwords for the attack. For example, a password of the value "password" can also be tried as p@$$word using the brute force attack.
• Rainbow table attack– This method uses pre-computed hashes. Let's assume that we have a database which stores passwords as md5 hashes. We can create another database that has md5 hashes of commonly used passwords. We can then compare the password hash we have against the stored hashes in the database. If a match is found, then we have the password.
• Guess– As the name suggests, this method involves guessing. Passwords such as qwerty, password, admin, etc. are commonly used or set as default passwords. If they have not been changed or if the user is careless when selecting passwords, then they can be easily compromised.
• Spidering– Most organizations use passwords that contain company information. This information can be found on company websites, social media such as facebook, twitter, etc. Spidering gathers information from these sources to come up with word lists. The word list is then used to perform dictionary and brute force attacks.

Spidering sample dictionary attack wordlist

1976 <founder birth year>

smith jones <founder name>

acme <company name/initials>

built|to|last <words in company vision/mission>

golfing|chess|soccer <founders hobbies

Password cracking tool

These are software programs that are used to crack user passwords. We already looked at a similar tool in the above example on password strengths. The website www.md5this.com uses a rainbow table to crack passwords. We will now look at some of the commonly used tools

John the Ripper

John the Ripper uses the command prompt to crack passwords. This makes it suitable for advanced users who are comfortable working with commands. It uses to wordlist to crack passwords. The program is free, but the word list has to be bought. It has free alternative word lists that you can use. Visit the product website http://www.openwall.com/john/ for more information and how to use it.

Cain & Abel

Cain & Abel runs on windows. It is used to recover passwords for user accounts, recovery of Microsoft Access passwords; networking sniffing, etc. Unlike John the Ripper, Cain & Abel uses a graphic user interface. It is very common among newbies and script kiddies because of its simplicity of use. Visit the product website http://www.softpedia.com/get/Security/Decrypting-Decoding/Cain-and-Abel.shtml for more information and how to use it.

Ophcrack

Ophcrack is a cross-platform Windows password cracker that uses rainbow tables to crack passwords. It runs on Windows, Linux and Mac OS. It also has a module for brute force attacks among other features. Visit the product website http://ophcrack.sourceforge.net/  for more information and how to use it.

Password Cracking Counter Measures

• An organization can use the following methods to reduce the chances of the passwords been cracked
• Avoid short and easily predicable passwords
• Avoid using passwords with predictable patterns such as 11552266.
• Passwords stored in the database must always be encrypted. For md5 encryptions, its better to salt the password hashes before storing them. Salting involves adding some word to the provided password before creating the hash.
• Most registration systems have password strength indicators, organizations must adopt policies that favor high password strength numbers.

Hacking Activity: Hack Now!

In this practical scenario, we are going to crack Windows account with a simple password. Windows uses NTLM hashes to encrypt passwords. We will use the NTLM cracker tool in Cain and Abel to do that.

Cain and Abel cracker can be used to crack passwords using;

• Dictionary attack
• Brute force
• Cryptanalysis

We will use the dictionary attack in this example. You will need to download the dictionary attack wordlist here 10k-Most-Common.zip

For this demonstration, we have created an account called Accounts with the password qwerty on Windows 7.

Password cracking steps

• Open Cain and Abel, you will get the following main screen

• Make sure the cracker tab is selected as shown above
• Click on the Add button on the toolbar.

• The following dialog window will appear

• The local user accounts will be displayed as follows. Note the results shown will be of the user accounts on your local machine.

• Right click on the account you want to crack. For this tutorial, we will use Accounts as the user account.

• The following screen will appear

• Right click on the dictionary section and select Add to list menu as shown above
• Browse to the 10k most common.txt file that you just downloaded

• Click on start button
• If the user used a simple password like qwerty, then you should be able to get the following results.

• Note: the time taken to crack the password depends on the password strength, complexity and processing power of your machine.
• If the password is not cracked using a dictionary attack, you can try brute force or cryptanalysis attacks.

Summary

• Password cracking is the art of recovering stored or transmitted passwords.
• Password strength is determined by the length, complexity, and unpredictability of a password value.
• Common password techniques include dictionary attacks, brute force, rainbow tables, spidering and cracking.
• Password cracking tools simplify the process of cracking passwords.

@EVERYTHING NT

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Save Your Cloud: Gain Root Access To VMs In OpenNebula 4.6.1

In this post, we show a proof-of-concept attack that gives us root access to a victim's VM in the Cloud Management Platform OpenNebula, which means that we can read and write all its data, install software, etc. The interesting thing about the attack is, that it allows an attacker to bridge the gap between the cloud's high-level web interface and the low-level shell-access to a virtual machine.

Like the latest blogpost of this series, this is a post about an old CSRF- and XSS-vulnerability that dates back to 2014. However, the interesting part is not the vulnerability itself but rather the exploit that we were able to develop for it.

An attacker needs the following information for a successful attack.

• ID of the VM to attack
  OpenNebula's VM ID is a simple global integer that is increased whenever a VM is instantiated. The attacker may simply guess the ID. Once the attacker can execute JavaScript code in the scope of Sunstone, it is possible to use OpenNebula's API and data structures to retrieve this ID based on the name of the desired VM or its IP address.
• Operating system & bootloader
  There are various ways to get to know a VMs OS, apart from simply guessing. For example, if the VM runs a publicly accessible web server, the OS of the VM could be leaked in the HTTP-Header Server (see RFC 2616). Another option would be to check the images or the template the VM was created from. Usually, the name and description of an image contains information about the installed OS, especially if the image was imported from a marketplace.
  Since most operating systems are shipped with a default bootloader, making a correct guess about a VMs bootloader is feasible. Even if this is not possible, other approaches can be used (see below).
• Keyboard layout of the VM's operating system
  As with the VMs bootloader, making an educated guess about a VM's keyboard layout is not difficult. For example, it is highly likely that VMs in a company's cloud will use the keyboard layout of the country the company is located in.

Overview of the Attack

The key idea of this attack is that neither Sunstone nor noVNC check whether keyboard related events were caused by human input or if they were generated by a script. This can be exploited so that gaining root access to a VM in OpenNebula requires five steps:

1. Using CSRF, a persistent XSS payload is deployed.
2. The XSS payload controls Sunstone's API.
3. The noVNC window of the VM to attack is loaded into an iFrame.
4. The VM is restarted using Sunstone's API.
5. Keystroke-events are simulated in the iFrame to let the bootloader open a root shell.

Figure 1: OpenNebula's Sunstone Interface displaying the terminal of a VM in a noVNC window.

The following sections give detailed information about each step.

Executing Remote Code in Sunstone

In Sunstone, every account can choose a display language. This choice is stored as an account parameter (e.g. for English LANG=en_US). In Sunstone, the value of the LANG parameter is used to construct a <script> tag that loads the corresponding localization script. For English, this creates the following tag:

<script src="locale/en_US/en_US.js?v=4.6.1" type="text/javascript"></script>

Setting the LANG parameter to a different string directly manipulates the path in the script tag. This poses an XSS vulnerability. By setting the LANG parameter to LANG="onerror=alert(1)//, the resulting script tag looks as follows:

<script src="locale/"onerror=alert(1)///"onerror=alert(1)//.js?v=4.6.1" type="text/javascript"></script>

For the web browser, this is a command to fetch the script locale/ from the server. However, this URL points to a folder, not a script. Therefore, what the server returns is no JavaScript. For the browser, this is an error, so the browser executes the JavaScript in the onerror statement: alert(1). The rest of the line (including the second alert(1)) is treated as comment due to the forward slashes.

When a user updates the language setting, the browser sends an XMLHttpRequest of the form

{ "action" : { "perform" : "update", "params" : { "template_raw" : "LANG=\"en_US\"" } }}

to the server (The original request contains more parameters. Since these parameters are irrelevant for the technique, we omitted them for readability.). Forging a request to Sunstone from some other web page via the victim's browser requires a trick since one cannot use an XMLHttpRequest due to restrictions enforced by the browser's Same-Origin-Policy. Nevertheless, using a self-submitting HTML form, the attacker can let the victim's browser issue a POST request that is similar enough to an XMLHttpRequest so that the server accepts it.

An HTML form field like

<input name='deliver' value='attacker' />

is translated to a request in the form of deliver=attacker. To create a request changing the user's language setting to en_US, the HTML form has to look like

<input name='{"action":{"perform":"update","params":{"template_raw":"LANG' value='\"en_US\""}}}' />

Notice that the equals sign in LANG=\"en_US\" is inserted by the browser because of the name=value format.

Figure 2: OpenNebula's Sunstone Interface displaying a user's attributes with the malicious payload in the LANG attribute.

Using this trick, the attacker sets the LANG parameter for the victim's account to "onerror=[remote code]//, where [remote code] is the attacker's exploit code. The attacker can either insert the complete exploit code into this parameter (there is no length limitation) or include code from a server under the attacker's control. Once the user reloads Sunstone, the server delivers HTML code to the client that executes the attacker's exploit.

Prepare Attack on VM

Due to the overwritten language parameter, the victim's browser does not load the localization script that is required for Sunstone to work. Therefore, the attacker achieved code execution, but Sunstone breaks and does not work anymore. For this reason, the attacker needs to set the language back to a working value (e.g. en_US) and reload the page in an iFrame. This way Sunstone is working again in the iFrame, but the attacker can control the iFrame from the outside. In addition, the attack code needs to disable a watchdog timer outside the iFrame that checks whether Sunstone is correctly initialized.

From this point on, the attacker can use the Sunstone API with the privileges of the victim. This way, the attacker can gather all required information like OpenNebula's internal VM ID and the keyboard layout of the VM's operating system from Sunstone's data-structures based on the name or the IP address of the desired VM.

Compromising a VM

Using the Sunstone API the attacker can issue a command to open a VNC connection. However, this command calls window.open, which opens a new browser window that the attacker cannot control. To circumvent this restriction, the attacker can overwrite window.open with a function that creates an iFrame under the attacker's control.

Once the noVNC-iFrame has loaded, the attacker can send keystrokes to the VM using the dispatchEvent function. Keystrokes on character keys can be simulated using keypress events. Keystrokes on special keys (Enter, Tab, etc.) have to be simulated using pairs of keydown and keyup events since noVNC filters keypress events on special keys.

Getting Root Access to VM

To get root access to a VM the attacker can reboot a victim's VM using the Sunstone API and then control the VM's bootloader by interrupting it with keystrokes. Once the attacker can inject commands into the bootloader, it is possible to use recovery options or the single user mode of Linux based operating systems to get a shell with root privileges. The hardest part with this attack is to get the timing right. Usually, one only has a few seconds to interrupt a bootloader. However, if the attacker uses the hard reboot feature, which instantly resets the VM without shutting it down gracefully, the time between the reboot command and the interrupting keystroke can be roughly estimated.

Even if the bootloader is unknown, it is possible to use a try-and-error approach. Since the variety of bootloaders is small, one can try for one particular bootloader and reset the machine if the attack was unsuccessful. Alternatively, one can capture a screenshot of the noVNC canvas of the VM a few seconds after resetting the VM and determine the bootloader.

A video of the attack can be seen here. The browser on the right hand side shows the victim's actions. A second browser on the left hand side shows what is happening in OpenNebula. The console window on the bottom right shows that there is no user-made keyboard input while the attack is happening.