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102 lines
2.7 KiB
Markdown
102 lines
2.7 KiB
Markdown
---
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title: "Writeup - Nibbles (HTB)"
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date: 2022-05-17
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slug: "writeup-nibbles-htb"
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type: "writeup-ctf"
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---
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This is a writeup for the [Nibbles](https://app.hackthebox.com/machines/Nibbles) machine from the HackTheBox site.
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## Enumeration
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First, let's start with a scan of our target with the following command:
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```bash
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nmap -sV -T4 -Pn 10.10.11.146
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```
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Two TCP ports are discovered:
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- 22/tcp : SSH port (OpenSSH 7.2p2)
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- 80/tcp : HTTP web server (Apache 2.4.18)
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## Exploit
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Looking at the source code of the web page I found the following comment:
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```bash
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<!-- /nibbleblog/ directory. Nothing interesting here! -->
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```
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So I go to this new page:
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I then search the pages present on the site with `ffuf`.
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One page is particularly interesting: `admin`.
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So I try to brute force the password of the `admin` user with the `hydra` command.
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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`.
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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/).
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I can now connect to the admin panel! After going through the panel, I find the following page where you can upload images.
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So I try to send a reverse shell in php, then I go to the following link to execute it:
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```bash
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10.10.10.75/nibbleblog/content/private/plugins/my_image/image.php
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```
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I now have a reverse shell as a `nibbler` and I can get the first flag.
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## Privilege escalation
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I start by checking the sudo permissions of my user:
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I find it in my personal folder a `.zip` file, I unzip it :
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The script can be modified by myself and can be executed as root. I put the following content in the script `monitor.sh` :
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```bash
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mkdir /root/.ssh
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touch /root/.ssh/authorized_keys
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echo 'id_rsa' > /root/.ssh/authorized_keys
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```
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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:
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```bash
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sudo -n ./monitor.sh
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```
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I can now log in as root and get the last flag.
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## Recommendations
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To patch this host I think it would be necessary to perform a number of actions:
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- Do not leave important comments in HTML code
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- Update NibbleBlog to fix file upload problem
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- Do not let user-modifiable scripts be executed by the root user
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