Vulnerable code sample

from flask import Flask, render_template
from jinja2.exceptions import TemplateNotFound

# In the vulnerable version, the application was effectively running in a
# debug-like state where unhandled exceptions would return a full traceback.
# This is simulated here by enabling Flask's debug mode.
app = Flask(__name__)
app.config['DEBUG'] = True

# The route is accessible without any authentication checks.
# It takes a path-like variable from the URL.
@app.route('/web/<path:filename>')
def serve_template(filename):
    """
    This function attempts to render a template using the filename
    provided by the user in the URL.
    """
    try:
        # If an attacker requests a template that does not exist,
        # e.g., /web/nonexistent.html, this line will raise
        # a TemplateNotFound exception.
        return render_template(filename)
    except TemplateNotFound:
        # In a properly configured app, this would be caught and a
        # generic 404 page would be returned. In the vulnerable code,
        # the exception was not handled, allowing the framework's debug
        # handler to expose the stack trace. To simulate this, we re-raise
        # the exception so the debug handler catches it.
        raise

# To run this example:
# 1. Save it as `vulnerable_app.py`.
# 2. Make sure you have Flask installed (`pip install Flask`).
# 3. Create an empty directory named `templates` in the same folder.
# 4. Run the script: `python vulnerable_app.py`.
# 5. Open your browser and navigate to `http://127.0.0.1:5000/web/does-not-exist.html`.
# You will see a detailed Flask debug page with the full traceback.
if __name__ == '__main__':
    # Note: Running with app.run() directly is not for production.
    # The vulnerability was in how the pyLoad application was packaged and run,
    # exposing these debug tracebacks.
    app.run(host='0.0.0.0', port=5000)