CVE-2021-23401

medium

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.

References

Advisories
More

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

Details

Source: Mitre, NVD

Published: 2021-07-05

Updated: 2026-06-17

Risk Information

CVSS v2

Base Score: 5.8

Vector: CVSS2#AV:N/AC:M/Au:N/C:P/I:P/A:N

Severity: Medium

CVSS v3

Base Score: 6.1

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Severity: Medium

CVSS v4

Base Score: 5.3

Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

Severity: Medium

EPSS

EPSS: 0.00265