CVE-2021-23401
CVE-2021-23401 is a medium-severity vulnerability in Flask-user Project Flask-user with a CVSS 3.x base score of 5.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-601.
Key facts
- Severity: Medium (CVSS 3.x base score 5.4)
- CVSS v2: 5.8
- EPSS exploit prediction: 1% (62nd percentile)
- Actively exploited: Not listed in CISA KEV
- Weakness: CWE-601
- Affected product: Flask-user Project Flask-user
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2021-23401?
- 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.
- How severe is CVE-2021-23401?
- CVE-2021-23401 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
- Is CVE-2021-23401 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (62nd percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2021-23401?
- CVE-2021-23401 affects Flask-user Project Flask-user. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2021-23401?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- When was CVE-2021-23401 published?
- CVE-2021-23401 was published on 2021-07-05 and last updated on 2026-06-17.
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
Affected products (1)
- cpe:2.3:a:flask-user_project:flask-user:*:*:*:*:*:*:*:*
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