This affects all versions of package Flask-Security. When using the get_post_logout_redirect and get_post_login_redirect functions, it is possible to bypass URL validation and redirect a user to an arbitrary URL by providing multiple back slashes such as \\\evil.com/path. This vulnerability is only exploitable if an alternative WSGI server other than Werkzeug is used, or the default behaviour of Werkzeug is modified using 'autocorrect_location_header=False. **Note:** Flask-Security is not maintained anymore.
https://snyk.io/blog/url-confusion-vulnerabilities/
https://security.snyk.io/vuln/SNYK-PYTHON-FLASKSECURITY-1293234
https://lists.debian.org/debian-lts-announce/2023/08/msg00034.html