What is CVE-2021-21337?

CVE-2021-21337 is a medium-severity vulnerability in Zope Products.pluggableauthservice, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 5.7/10. Published 2021-03-08.

How severe is CVE-2021-21337?

Medium severity. CVSS v3 base score is 5.7 out of 10.

Is CVE-2021-21337 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Open Redirect in Zope Products.pluggableauthservice

CVE-2021-21337

Products.PluggableAuthService is a pluggable Zope authentication and authorization framework. In Products.PluggableAuthService before version 2.6.0 there is an open redirect vulnerability. A maliciously crafted link to the login form and login functionality could redirect the browser to a different website. The problem has been fixed in version 2.6.1. Depending on how you have installed Products.PluggableAuthService, you should change the buildout version pin to `2.6.1` and re-run the buildout, or if you used `pip` simply do `pip install "Products.PluggableAuthService>=2.6.1".

Vulnerability class: Open Redirect

Published 2021-03-08 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.7 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.084 (94.8th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 95th percentile — 94.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.084 · newest: 0.084 · change: 0.000

Affected products

Zope Products.pluggableauthservice
Zopefoundation Products.pluggableauthservice — versions < 2.6.1

Weakness classification (CWE)

CWE-601 — URL Redirection to Untrusted Site (Open Redirect)

Public proof-of-concept exploits

ARPSyndicate/cvemon

References

pypi.org/project/Products.PluggableAuthService/ (Product, Third Party Advisory)
github.com/zopefoundation/Products.PluggableAuthService/security/advisories/GHS… (Third Party Advisory)
github.com/zopefoundation/Products.PluggableAuthService/commit/7eead067898852eb… (Patch, Third Party Advisory)
packetstormsecurity.com/files/162911/Products.PluggableAuthService-2.6.0-Open-R… (Exploit, VDB Entry, Third Party Advisory)

Frequently asked questions

What is CVE-2021-21337?: CVE-2021-21337 is a medium-severity vulnerability in Zope Products.pluggableauthservice, classified under URL Redirection to Untrusted Site (Open Redirect). CVSS score: 5.7/10. Published 2021-03-08.
How severe is CVE-2021-21337?: Medium severity. CVSS v3 base score is 5.7 out of 10.
Is CVE-2021-21337 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.