---
title: "Writeup - Nibbles (HTB)"
date: 2022-05-17
slug: "writeup-nibbles-htb"
type: "writeup-ctf"
--- 

This is a writeup for the [Nibbles](https://app.hackthebox.com/machines/Nibbles) machine from the HackTheBox site.

## Enumeration

First, let's start with a scan of our target with the following command:


```bash
nmap -sV -T4 -Pn 10.10.11.146
```
Two TCP ports are discovered:

![](img/image-1.webp)

- 22/tcp : SSH port (OpenSSH 7.2p2)
- 80/tcp : HTTP web server (Apache 2.4.18)

## Exploit

Looking at the source code of the web page I found the following comment:


```bash
<!-- /nibbleblog/ directory. Nothing interesting here! -->
```
So I go to this new page:

![](img/image-2.webp)

I then search the pages present on the site with `ffuf`.

![](img/image-3.webp)

One page is particularly interesting: `admin`.

![](img/image-4.webp)

So I try to brute force the password of the `admin` user with the `hydra` command.

![](img/image-5.webp)

Although the command finds several results it does not work. Indeed there is an anti-brute force security. So I try to test common passwords and after a few tries I find the following credentials: `admin/nibbles`.

It's good but rather frustrating not to have found a more legit way. After some research I find a solution online to test passwords taking into account the anti brute force: [brute force version](https://eightytwo.net/blog/brute-forcing-the-admin-password-on-nibbles/).

I can now connect to the admin panel! After going through the panel, I find the following page where you can upload images.

![](img/image-6.webp)

So I try to send a reverse shell in php, then I go to the following link to execute it:


```bash
10.10.10.75/nibbleblog/content/private/plugins/my_image/image.php
```
I now have a reverse shell as a `nibbler` and I can get the first flag.

![](img/image-7.webp)

## Privilege escalation

I start by checking the sudo permissions of my user:

![](img/image-8.webp)

I find it in my personal folder a `.zip` file, I unzip it :

![](img/image-9.webp)

The script can be modified by myself and can be executed as root. I put the following content in the script `monitor.sh` :


```bash
mkdir /root/.ssh
touch /root/.ssh/authorized_keys
echo 'id_rsa' > /root/.ssh/authorized_keys
```
This will create the SSH folder of the root user and then add my key in the `authorized_keys`. To execute the script I use the following command:


```bash
sudo -n ./monitor.sh
```
I can now log in as root and get the last flag.

![](img/image-10.webp)

## Recommendations

To patch this host I think it would be necessary to perform a number of actions:

- Do not leave important comments in HTML code
- Update NibbleBlog to fix file upload problem
- Do not let user-modifiable scripts be executed by the root user