Created attachment 1190639 [details]
the markdown file

Description of problem:
If a website developed by python-flask or other werkzeug-base framework run in debug mode which use the Debugger of werkzeug,it may be XSS by triggering an error。

Version-Release number of selected component (if applicable):
<= 0.11.10

How reproducible:

Steps to Reproduce:
1. For example, a common Flask 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'])
    # or id = int(request.args.get('id'))
    return "XSS"

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

2. If the hacker posted “id=1</textarea><script>alert(/XSS/)</script>” to the url "/xss-debug-test/", the JavaScript in payload will be run in client.

Additional info:

The problem code is in the werkzeug/debug/tbtools.py, line 349:

def render_full(self, evalex=False, secret=None,
evalex_trusted=True):
"""Render the Full HTML page with the traceback info."""
exc = escape(self.exception) # the exception info use the escape method
return PAGE_HTML % {
'evalex': evalex and 'true' or 'false',
'evalex_trusted': evalex_trusted and 'true' or 'false',
'console': 'false',
'title': exc,
'exception': exc,
'exception_type': escape(self.exception_type),
'summary': self.render_summary(include_title=False),
'plaintext': self.plaintext, # the plaintext did not use the escape method
'plaintext_cs': re.sub('-{2,}', '-', self.plaintext),
'traceback_id': self.id,
'secret': secret
}

See the code, the 'exc' variable use the escape method, but the 'plaintext' variable did not use. And it contained the exception info too in generate_plaintext_traceback function.