Description of problem:
If a website developed by python-flask run in debug mode,can be XSS by triggering an error。

Version-Release number of selected component (if applicable):
<= 0.11.1

How reproducible:

Steps to Reproduce:
1.For example,code:

from flask import Flask, request
app = Flask(__name__)

@app.route("/xss-debug-test/", methods=['POST'])
def xss_debug_test():
    id = int(request.form['id'])
    return "Hello World!"

if __name__ == "__main__":
    app.run(debug=True)


2.if the hacker posted "id=1</textarea><script>alert(/XSS/)</script>",the JavaScript in payload will be run in client.

Actual results:


Expected results:


Additional info: