CVE-2021-23401: Open Redirect

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.1% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-07-05 · updated 2026-06-17
Weakness: CWE-601

Description

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

Flask-User: all versions

References

https://github.com/lingthio/Flask-User
https://github.com/lingthio/Flask-User/blob/master/flask_user/user_manager__utils.py
https://snyk.io/vuln/SNYK-PYTHON-FLASKUSER-1293188
https://github.com/lingthio/Flask-User
https://github.com/lingthio/Flask-User/blob/master/flask_user/user_manager__utils.py
https://snyk.io/vuln/SNYK-PYTHON-FLASKUSER-1293188

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