CVE-2021-23385

Name: CVE-2021-23385
Creator: NVD / NIST
Published: 2022-08-02T14:15:10.017+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.1/10EPSS 0.90%

Last modified Jun 17, 2026

CVE-2021-23385 is a medium-severity vulnerability rated 6.1/10 on the CVSS scale. This affects all versions of package Flask-Security. When using the get_post_logout_redirect and get_post_login_redirect functions, 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. EPSS estimates a 0.90% chance of exploitation in the next 30 days.

Description

This affects all versions of package Flask-Security. When using the get_post_logout_redirect and get_post_login_redirect functions, 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. 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. **Note:** Flask-Security is not maintained anymore.

Metrics

CVSS 3.1

6.1/10

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

EPSS Probability

0.90%

54.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-601

Affected Software

Vendor	Product	Versions
Flask-Security Project	Flask-Security	All versions

References

https://github.com/mattupstate/flask-securityProduct, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2023/08/msg00034.html
https://security.snyk.io/vuln/SNYK-PYTHON-FLASKSECURITY-1293234Exploit, Third Party Advisory
https://snyk.io/blog/url-confusion-vulnerabilities/Technical Description, Third Party Advisory
https://github.com/mattupstate/flask-securityProduct, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2023/08/msg00034.html
https://security.snyk.io/vuln/SNYK-PYTHON-FLASKSECURITY-1293234Exploit, Third Party Advisory
https://snyk.io/blog/url-confusion-vulnerabilities/Technical Description, Third Party Advisory

Timeline

Published: Aug 2, 2022
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-23385?

How severe is CVE-2021-23385?

CVE-2021-23385 has a CVSS score of 6.1/10 (MEDIUM severity). The EPSS model estimates a 0.90% probability of exploitation in the next 30 days.

How do I fix CVE-2021-23385?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-23385?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST