Nibbles | Hack the box

Executive Summary

The administrator password was easily guessable which allows any user to gain access to the administration dashboard. Having that access the attacker can leverage the fact that the blog is running a version that is out of date. Any attacker could utilize the vulnerabilities within the blog to gain access to the host running the blog and run commands on it. Moreover, the user within the server has access to run a specific file as the super admin user ( root ) which can allow the attacker to control the server with no limits.

Recon

first let's add the IP of the target to the host file and name it nibbles.htb

<target-ip> nibbles.htb

Before throwing any nmap scans at the target it is a good practice to just go to the browser and try to browse to it. this will allow us to discover if port 80 is open without making any scans.

Doing so shows that indeed port 80 is open and we are greeting with a simple hello world string

doing a curl on it shows us some interesting information

curl -L http://nibbles.htb # -L to follow any redirections

we found the following comment

<!-- /nibbleblog/ directory. Nothing interesting here! -->

going to that page we find the homepage of the nibbleblog

Running scans

now that we found the page lets run some scans.

1. running Nmap to find other ports

2. scanning the site with gobuster to find interesting directories

gobuster

running gobuster like

gobuster dir -u http://nibbles.htb/nibbleblog/ -w /usr/share/wordlists/dirb/common.txt

this shows that there is an admin.php page

Also the /admin path leads to showing some interesting folders that should not be visible by anyone

Also, there is another folder called /content which is interesting

Let's enumerate to find out if we can find any legit user names or passwords

bingo going to the /content/private we found the users.xml file which gives us a few important clues

1. there is a user called admin

2. there is a rate limit so if we try many times we will get locked out so we cannot throw hydra at it and brute force the login.

Attempting login

I tried to manually guess the password of the admin user and we found that it is nibbles

logging into the admin area we found that the version of nibblesblog running is 4.0.3

Vulnerabilities

searching for this version we can quickly find that there is a file upload vulnerability https://www.exploit-db.com/exploits/38489 with a metasploit module https://www.rapid7.com/db/modules/exploit/multi/http/nibbleblog_file_upload/

exploit description https://packetstormsecurity.com/files/133425/NibbleBlog-4.0.3-Shell-Upload.html

Nmap Result

The Nmap scan took a while but found only 2 ports open 80 and 22 finding the service version with the default scripts we find that the target is running

22/tcp open  ssh     OpenSSH 7.2p2 Ubuntu 4ubuntu2.2
80/tcp open  http    Apache httpd 2.4.18 ((Ubuntu))

Apache 2.4.18 doing a searchsploit on version 2.4 we find a buffer overflow exploit on version 2.4.x

multiple/webapps/51193.py

https://www.exploit-db.com/exploits/51193 Note: this exploit requires a path to a .lua file which we don't have at the moment

OpenSSH 7.2p2 doing a searchsploit on openssh with this version we find a vulnerability that allows us to enumerate usernames https://www.exploit-db.com/exploits/40136 we can also use metasploit module for this https://www.rapid7.com/db/modules/auxiliary/scanner/ssh/ssh_enumusers/

Exploitation

File Upload Vulnerability

Following the description in https://packetstormsecurity.com/files/133425/NibbleBlog-4.0.3-Shell-Upload.html

When uploading image files via the "My image" plugin - which isdelivered with NibbleBlog by default - , NibbleBlog 4.0.3 keeps theoriginal extension of uploaded files. This extension or the actual filetype are not checked, thus it is possible to upload PHP files and gaincode execution.

we can utilize the php reverse shell file located in /usr/share/web-shells and updating our IP Note: the above reverse shell did not work ( the shell keeps hanging )so we utilized a simple shell with cmd and then url encoded the reverse temp shell and passed it to get a revshell address to get a shell then we can start a netcat listener in our machine

nc -lvnp 1234

once we visit the image.php we will get a shell now we visit

http://nibbles.htb/nibbleblog/content/private/plugins/my_image/image.php

now we need to stabilize our shell we run

which python

and we could not find Python on the server we run

which python3

and bingo, it is there so we run

python3 -c 'import pty;pty.spawn("/bin/bash")'

and we get a better shell however we still have to do more. we click ctrl+Z to background it and then

stty raw -echo; fg

then we hit enter twice and now we have a stable shell.

Local enumaration

now that we are on the server we need to enumerate to find more information

running

whoami

we found that we are running as the nibbler user

we go to the home folder of nibbler user and we find the user.txt which contains the user flag. we can also find a zip file called personal.zip so we unzip it.

Now Running

sudo -l

we find out that we can run /home/nibbler/personal/stuff/monitor.sh as root with NO Password

Now all we have to do is add the line

/bin/bash

to monitor.sh and run it with sudo. it will not ask for a password and we will drop in a shell with root access.