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Introduction to Flask - Write-up - TryHackMe

noraj (Alexandre ZANNI)
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Information

Room#

  • Name: Introduction to Flask
  • Profile: tryhackme.com
  • Difficulty: Easy
  • Description: How it works and how can I exploit it?

Introduction to Flask

Write-up

Installation and Deployment basics#

Which environment variable do you need to change in order to run Flask?

Answer: FLASK_APP

Clone the example repository:

$ git clone https://github.com/Swafox/Flask-examples

Create a virtual environment:

$ cd Flask-examples
$ python -m venv venv
$ source venv/bin/activate

Install flask:

$ pip3 install Flask

Choose the app to run and run it:

$ export FLASK_APP=helloworld.py
$ flask run

Basic syntax and routing#

What's the default deployment port used by Flask?

Answer: 5000

Check in your terminal.

Is it possible to change that port? (yay/nay)

Answer: yay

$ flask run --help | grep port
  -p, --port INTEGER              The port to bind to.

HTTP Methods and Template Rendering#

Does Flask support POST requests? (yay/nay)

Answer: yay

httpmethods.py

from flask import request

def do_the do_the_login():
	return 'This was a POST request'

def show_the_login_form():
	return 'Not POST. Are you GETting me? :)'

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        return do_the_login()
    else:
        return show_the_login_form()

What markup language can you use to make templates for Flask?

Answer: html

templaterendering.py

from flask import render_template

@app.route('/rendered')
def hello(name=None):
    return render_template('template.html', name=name)


'''
HTML example:
<!doctype html>
<title>Hello from Flask</title>
<h1>Hello again, TryHackMe</h1>
'''

Flask Injection#

What's inside /home/flask/flag.txt ?

Answer: THM{flask_1njected}

Use a LFI in the SSTI: http://10.10.17.26:5000/vuln?name={{%20get_user_file(%22/home/flask/flag.txt%22)%20}}

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