Port Wine: CTF Challenge

A Capture The Flag (CTF) challenge focused on network security, where participants exploit vulnerabilities in a Flask web application running on multiple ports to retrieve hidden flags.

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Creators

Kshitij Koushik Kota - https://github.com/kshitijkota
Sampriti Saha - https://github.com/Sampriti2803

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Challenge Overview

• Challenge Name: Port Wine
• Category: Network Security
• Difficulty Level: Medium
• Description: Participants will utilize network scanning and exploitation techniques to identify and extract hidden flags from multiple Flask applications running on different ports.

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Objective

The goal is to retrieve the flag hidden within the Flask web application by:

• Identifying open ports and running services.
• Understanding application behavior and potential vulnerabilities.
• Extracting hidden flags using various techniques, including Brainfuck decoding.

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Setup Instructions

1. Environment Preparation

• Server Setup: Deploy the Flask application on a virtual machine (VM) or cloud server.
• Operating System: Recommended Linux (Ubuntu) environment.
• Install Dependencies:

  sudo apt update && sudo apt install python3 python3-pip
  pip install flask

2. Running the Flask Application

1. Clone the repository:

   git clone https://github.com/yourusername/port-wine-ctf.git
   cd port-wine-ctf

2. Start the Flask applications:

   python3 index.py

3. The applications will run on the following ports:
   • 8000
   • 5001
   • 8080
   • 4000

3. Understanding the Web Application

• The homepage (/) serves an index.html file from the public directory (on port 8000).
• The /flag route on different ports reveals different clues to retrieve the final flag.

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Challenge Walkthrough

1. Scan for Open Ports

Use Nmap to identify active services:

nmap [Server_IP]

For more detailed version detection:

nmap -sV [Server_IP]

Expected open ports: 8000, 5001, 8080, 4000

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2. Retrieving the Flags

1. Port 5001

   • Access:

     curl http://[Server_IP]:5001/flag

   • Returns a Google Drive link containing an encrypted flag.pdf.

2. Port 8080

   • Access:

     curl http://[Server_IP]:8080/flag

   • Returns an encoded password: Flag4_Txt_Op3n#

3. Port 8000 & 4000

   • No useful flags are found.

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3. Decoding the Password & Extracting the Flag

1. The password retrieved from port 8080 is Brainfuck-encoded.
2. Decode it using a Brainfuck interpreter.
3. Use the decoded password to unlock flag.pdf.

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Flag Format

• The final flag should be in the format:

  CTF{hidden_flag}

• Ensure the flags are not exposed in the source code.

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License

This project is licensed under the MIT License.