Flask-RESTX (pypi package flask-restx) is a community driven fork of Flask-RESTPlus. Flask-RESTX before version 0.5.1 is vulnerable to ReDoS (Regular Expression Denial of Service) in email_regex. This is fixed in version 0.5.1.
https://pypi.org/project/flask-restx/
https://github.com/python-restx/flask-restx/issues/372
https://github.com/python-restx/flask-restx/commit/bab31e085f355dd73858fd3715f7ed71849656da