robsware

The vulnerability is Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

python
from flask import Flask, request, redirect, render_template_string

app = Flask(__name__)

@app.route('/', methods=['GET', 'POST'])
def index():
    if request.method == 'POST':
        user_name = request.form.get('username')
        return render_template_string('Hello, !', user_name=user_name)

    return '''
    <form method="POST">
        <input type="text" name="username" placeholder="Enter your name">
        <input type="submit" value="Submit">
    </form>
    '''

if __name__ == '__main__':
    app.run(port=8000)

To fix the vulnerability, you need to sanitize user input by escaping any potentially harmful characters. In Python, you can use the `html.escape()` function from the `html` module to escape characters that have special meaning in HTML. In the code above, `sanitized_user_name` is created by escaping `user_name` input, and then `sanitized_user_name` is used in the template rendering. This way, any HTML tags and other potentially harmful input will be rendered as plain text instead of being executed by the browser.

python
from flask import Flask, request, redirect, render_template_string
import html

app = Flask(__name__)

@app.route('/', methods=['GET', 'POST'])
def index():
    if request.method == 'POST':
        user_name = request.form.get('username')
        sanitized_user_name = html.escape(user_name)
        return render_template_string('Hello, !', user_name=sanitized_user_name)

    return '''
    <form method="POST">
        <input type="text" name="username" placeholder="Enter your name">
        <input type="submit" value="Submit">
    </form>
    '''

if __name__ == '__main__':
    app.run(port=8000)