Open Redirect in Flask-User
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 backslashes 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 software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | flask-user | <= 1.0.2.2 | no fix |
References
- 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://github.com/advisories/GHSA-4298-89hc-6rfv
- https://nvd.nist.gov/vuln/detail/CVE-2021-23401
- https://github.com/pypa/advisory-database/tree/main/vulns/flask-user/PYSEC-2021-337.yaml
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N- Weakness (CWE)
CWE-601- Platform
- Python (PyPI)
- Package
flask-user- Disclosed
- 05.07.2021
- Updated
- 11.10.2026 11:20
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2021-337 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-4298-89hc-6rfv - CC BY 4.0
Vulnerability history: flask-user
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
This is the only known vulnerability of this package.
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