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Fencer Vulns
medium 5.4

CVE-2021-23385 json

Open Redirect

published 2022-08-02 4 y ago modified 2026-07-07 4 mo ago also GHSA-cg8c-gc2j-2wf7 , PYSEC-2026-809 , EUVD-2022-7078

cvss
5.4
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 69%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi flask-security 5.5.1
  • flask-security Debian 14, Debian 13, Debian 12 5.0.2-1

debian advisories DEBIAN-CVE-2021-23385

  • flask-security Ubuntu 20.04 LTS 1.7.5-2ubuntu0.20.04.1
  • flask-security Ubuntu 22.04 LTS 4.0.0-1ubuntu0.1
  • flask-security Ubuntu Pro 18.04 LTS 1.7.5-2ubuntu0.18.04.1~esm1

ubuntu advisories UBUNTU-CVE-2021-23385

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • python-Flask-Security-Too SLE Module for Basesystem 15 SP4, SLE Module for Basesystem 15 SP3, openSUSE Leap 15.4 +1 more 3.4.2-150200.3.6.1
  • python-Flask-Security openSUSE Leap 15.4, openSUSE Leap 15.3 3.0.0-150100.4.3.1

suse advisories SUSE-SU-2022:3867-1SUSE-SU-2022:3834-1

  • python-Flask-Security openSUSE Tumbleweed 5.5.2-1.1

opensuse advisories openSUSE-SU-2024:14555-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-23385 updated

python-flask-security: url validation bypass

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.25% chance of exploitation in the next 30 days, higher than 69% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • security.snyk.io https://security.snyk.io/vuln/SNYK-PYTHON-FLASKSECURITY-1293234 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.4 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N/E:P/RL:U/RC:C
CNA 3.1 5.4 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
NVD 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
OSV 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
GitHub 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
pypi flask-security
<=3.0.0
<5.5.1
5.5.1

Affected products

  • n/a Flask-Security

Classification

Weakness
  • CWE-601 URL Redirection to Untrusted Site

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.