CVE-2021-23401: Flask-User Project Flask-User

Medium severity, CVSS 6.1. EPSS: 1.1% chance of exploitation in the next 30 days.

This affects all versions of package Flask-User. When using the make_safe_url function, 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 or \\\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.

Affected products

Published 2021-07-05. Last modified 2026-06-17.