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GNU Debugger : Step By step Guide

Hello aspiring ethical hackers. In this howto, you will learn about GNU Debugger, step by step, A debugger is a computer program used to test the working of and debug other programs. Debugging means breaking down the program to see if it has any bugs or working glitches. These bugs can also be vulnerabilities although most of the times they are random behavior or unexpected behavior of the program (like crashing).

A debugger does debugging by running the target program under controlled conditions. GNU debugger more popular as GDB, is one such debugger. It can do four main things for us : Starting the program we want to test, Stop the program at certain points, examine what has happened when the program has stopped and change things in the target program allowing us to experiment. It is a portable debugger and runs on Windows, UNIX and Mac OS X. It can be used to debug programs of the given programming languages below.


1. Ada 2. Assembly 3. C 4. C++ 5. D 6. Fortran 7. Go 8. Objective-C 9. OpenCL 10. Modula-2 11. Pascal 12. Rust

Now let’s learn about this tool practically. We are doing this on Kali Linux OS (any version) as GNU debugger is provided by default in it. We create a new directory named “C” and move into that directory.

In that folder, use your favorite text editor to create a script named “first.c” and code a C program as shown below (Type it, don’t copy, you will thank us later).

As can be seen, it is a simple C program that adds two numbers given to it. Once the program is finished, save the file and compile the program using GCC compiler as shown below. Compiling the program is the process of turning it into machine language. This can be done using command gcc first.c -g -o first.

The “-g” option enables debugging. Once it is in machine code, we can execute it and see if it is working. It can be done in Linux as ./first. As we coded it, the program first asks the user to enter the first number. Once it is over, it asks user to enter the second umber. When both numbers are entered, it will ad -d them both and print the result after adding them both.

The program is running smoothly as intended. Now, let’s load this in the gdb debugger as shown below.

How to use GNU Debugger

Now let’s run the program once again inside the debugger. This can be done either using command r or run.

Now, in case you forgot the code of the program and can’t remember what it does you have no need to go out of the debugger. Using “l” or “list” command will show the first 10 lines of the code as shown below.

Now let’s add a break point at a certain line of the program. Break points allow us to stop the program at a certain point we want. A break point can be added using command “break” or “b“. Run the program again to see if the program stops at the intended point.

It stops exactly at line 9. The disable command disables the latest break point.

Now we set a break point at line 10 and want to see something. As the program stops at line 10, we can only enter one value that of variable “a”. We can use the print command to see the values of variables we have assigned.

While the value of “a” is something we set and it displaying correctly, we did not yet set the value for variable “b”. But it is still showing some random value. We can change the values we already set using the “set” command as shown below.

We set another break point and all the breakpoints set to the program can be seen using command “info b“.

Although there are three breakpoints, see that only two of them are active as we disabled one already. Let’s run the program again.

It stops at the break point which is at line 10. To completely remove the breakpoint use command “clear“.

Now there are only two breakpoints. To continue running the program from this point, use command “continue“. This will run the program from the exact point where it stopped. The program exited normally. “clear” command can be used to delete break points using their line number as shown below.

Let’s run the program again after removing all the break points .

Now, let’s set three new break points again on lines 9, 11 and 16. We will assign the values as the program executes.

At the first break point, I set the value of variable “a” to 19.5 and continue the program. I use the print command to see the value of variable “a”.

As you can see, it is printed as 19 and not 19.5. Our first bug. Similarly the “b” variable is 17 whereas we gave it the value of 17.6.

When we continue the program as it is, the answer we got is 32786 which is definitely wrong. Here we detected that the program is behaving abnormally when decimal numbers are given as input.

Here’ s another example.

Seeing this we can conclude that this program is only suitable for non decimal numbers and result goes wrong even if one of them is a decimal number. Using gdb we found out our first bug in a program. We can even see the assembly code of this program using the “disass” command.

But more about this in our future articles, That was all about Gnu debugger.

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Shellcode Injection with Metasploit

Shellcode Injection Module is a Metasploit module which as its name suggests, injects shellcode into the target Windows system on which we already have access. In our previous article, we have learnt what is shellcode and how it is created. Shellcode is a bit assembly code or machine language and it plays a very important role in cyber security. Typically shellcode is used in offensive penetration testing.

Let’ s see how this module works. Get a meterpreter session on a Windows system. Background the current session and load the post windows shellcode inject module as shown below.

We will use Donut tool to create a shellcode of the mimikatz program. Mimikatz is a tool used to experiment with Windows security. Its known to extract plaintext passwords and kerberos tickets from memory. It can also perform pass-the-hash, pass-the-ticket or build Golden tickets.

Set the SESSION ID and other options given below.

Set the interactive option to TRUE . We need to do this so that we are not taken directly to the mimikatz shell. We also need to set the correct target architecture.

After all the options are set, we need to just execute the module as shown below.

shellcode injection with Metasploit

That’s all about the Metasploit Shellcode Injection Module.

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Donut shellcode generator

Donut shellcode generator is a tool that generates shellcode from VBScript, JScript, EXE, DLL files and DOTNET assemblies. Although there are many tools that can do this, Donut does this with position independent code that enables in-memory execution of the compiled assemblies. This compiled shellcode assembly can either be staged from a HTTP server or embedded directly in the file itself. After the compiled shellcode is loaded and executed in memory, the original reference is erased immediately to avoid memory scanners.

The features supported by the Donut generator are

  1. Compression of the generated files with aPLib and LZNT1, Xpress, Xpress Huffman.
  2. Using entropy for generation of strings 128-bit symmetric encryption of files.
  3. Patching Antimalware Scan Interface (AMSI) and Windows Lockdown Policy (WLDP).
  4. Patching command line for EXE files.
  5. Patching exit-related API to avoid termination of host process.
  6. Multiple output formats: C, Ruby, Python, PowerShell, Base64, C#, Hexadecimal.
  7. What exactly is shellcode? Shellcode is a bit assembly code or machine language. Shellcode plays a very important role in cyber security. Typically shellcode is used in offensive penetration testing. In this article, let us learn about this awesome tool. This tool can be installed in Kali Linux by cloning it from Github as shown below. This will create a new directory named “Donut”
donut1

Navigating into the Donut shellcode generator directory, let’s create the shellcode of mimikatz.exe as shown.

How to use donut shellcode generator

Mimikatz.exe is a simple tool that is used to play with windows security. If you take this executable of Mimikatz into a Windows system, any antivirus or Windows Defender will detect this as malware. Just try it on your machine first before turning it into shellcode. It is found in Kali Linux. Here we copied it into the Donut folder.
When we run above command, shellcode is created as a file named “loader.bin” in the same directory of Donut.

By default, Donut creates shellcode for x86 (32bit) and amd64 (64bit). To create only a x86 shellcode, the command is as shown below.

The “-b” option is used to set the shellcode’s behavior when faced with AMSI/WLDP. Anti Malware Scan Interface and Windows Lock Down Policy are security features. These both features help in defending against malware.

By default, Donut sets the shellcode to bypass AMSI/WLDP. By setting the “-b” option to “2” as shown in the above image, it can be set to ABORT once it encounters AMSI/WLDP. Setting “1 ” will do nothing.
Entropy in general terms means the degree of randomness. It is used in malware to make detection of its code harder by Anti malware. This is called obfuscation. The more the entropy the least chances of detection of malware. Donut by default sets random names and al- so encrypts the shellcode to obfuscate the code from anti malware. It can be changed using the “-e” option. Setting it to “2” just sets random names to the payload and setting it to “1” does nothing.

Not just binaries, we can create different output formats with Donut although by default it creates a binary payload. The “-f” option is used to set different output formats. For example, set -ting “-f” option to “2” gives a base64 format. 3 creates C, 4 creates Ruby, 5 creates Python, 6 creates Powershell, 7 creates C# and 8 creates Hexadecimal shellcodes respectively.

The “-z” option is used to setting packing and compressing engines. Donut doesn’t use any compression by default. However it supports four compression engines. 2=aPLib, 3=LZNT1, 4=Xpress, 5=Xpress Huffman. Only the aPlib compressor works in Linux. Rest of them work in windows. Compression reduces the size of the payload whereas packing is used to avoid detection by anti malware.

We have seen that by default, Donut saves the payloads it creates in the same directory. The location as to where the payload is saved can be changed with the “-o” option.

That’s all about the Donut shellcode generator, readers. We will learn more about this tool and how it is used in real world ethical hacking.

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Parrot OS VirtualBox installation using ISO File

Hello aspiring ethical hackers. In this article, you will see how to install Parrot Security ISO in VirtualBox. In our previous article readers have seenhow to install Parrot Security OS in VirtualBox using OVA file (VirtualBox image file). In this article, readers will see how to install Parrot Security OS in VirtualBox using ISO file. Download the Parrot security ISO file from here. Once ISO file is finished downloading, open VirtualBox, go to Machine > New or hit CTRL+N as shown below.

A new window will open as shown below.

Click on “Expert mode”.

How to install parrot os virtualbox

Fill up the details. Configure the machine folder, type of OS, version etc and allocate the RAM (RAM should be minimum 2GB). Once everything is configured, Click on “Create”.

Allocate the hard-disk size (minimum 16 GB is the minimum requirement but keep it at least 20 GB). Set the other options as shown below. Click on “Create”.

The virtual machine is created. Start the newly created virtual machine. It should start as shown below.

Browse to the ISO file we downloaded earlier and add it as shown below. Then, click on “Start”.

The interface changes as shown below. Click on “Install”.

Once you are at the OS interface, click on “Install Parrot “. The Calamares Installer opens.

Click on “Next “. Select Location and click on “Next”.

Select the keyboard mode and click on “Next”.

Set the partition. Select “Erase disk” and click on “Next”.

Create a user and set credentials to the newly created user.

Review all the settings and click on “Install”.

Click on “Install Now.”

The system starts installing as shown below.

Once the system has finished installing as shown below, click on “Done” .

This will restart the system and will take you to the Login screen. Login using credentials of the newly created user and you are good to go. Happy hacking.

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Installing MATE Desktop in Kali Linux

Hello readers. Today our readers will learn about installing mate desktop in Kali Linux. You all know the first release of Kali Linux this year, Kali Linux 2020.1 has been released in the month of January. The latest version brought many changes like not giving root user by default and some new tools. The most distinct change it brought is a single installer image for installation. Earlier we had different installation images for different desktop environments which include GNOME, KDE etc.
With 2020.1 release, there will be a single installation image for all these and users would have to select the desktop environment he/she needs while installing. The information about different desktop environments and their pros and cons can be seen here.

Today we will see a tutorial on how to install MATE Desktop environment in Kali Linux 2020.1. MATE Desktop although looks old fashioned is light and has a simple interface. Here’s how to install MATE desktop environment in Kali Linux 2020.1. We have performed this tutorial from a X11 terminal but all these commands can be run from any other desktop environment’s terminal. Power on the Kali 2020.1 virtual machine and login (since there is no root user you should login as a user you created or the default user:password i.e kali:kali).

Open a terminal and using nano open the file /etc/apt/sources.list. with sudo

Add these two lines of code to the file and save it.
deb http://kali.download/kali kali-rolling main non-free contrib
deb-src http://kali.download/kali kali-rolling main non-free contrib

To save the file hit CTRl+X and when it prompts select “Yes”.Run command sudo apt-get update

Now everything is ready to install MATE desktop. Run the command given below.
sudo apt-get install mate-core mate-desktop-environment-extra mate-desktop-environment-extras

installing mate desktop in kali

When the system prompts you for permission to install MATE and its related software, type “Y”.

The installation will take some time to finish. After the installation is finished, restart the system (the command is sudo reboot or reboot if you are doing it from terminal). Once the system reboots and takes you to the login screen, before logging in click on the “settings” icon beside the “Signin” button. There you will see all the desktop environments present on the system right now. Select MATE and then login.

Installing MATE desktop has been successfully finished with this.

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