How severe is CVE-2021-33507?

CVE-2021-33507 has a CVSS score of 6.1/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-33507?

CVE-2021-33507 affects the following packages: products-cmfcore (PyPI), products-pluggableauthservice (PyPI), plone (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2021-33507?

Update products-cmfcore to 2.5.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33507 is resolved across your whole dependency graph.

How do I detect CVE-2021-33507 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for products-cmfcore, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-33507 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2021-33507 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-33507 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-33507?

CVE-2021-33507 has an EPSS (Exploit Prediction Scoring System) score of 0.8%, placing it in the 54th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-33507?

CVE-2021-33507 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2021-33507 published, and has it been updated?

CVE-2021-33507 was published on May 21, 2021 and was last updated on July 13, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

MEDIUM severity

CVE-2021-33507 — products-cmfcore

MEDIUM

CVE-2021-33507 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in products-cmfcore. A fix is available for products-cmfcore — see the affected versions and patch details below.

Cross-site scripting in Products.CMFCore, Products.PluggableAuthService, Plone

Also known asGHSA-35rg-466w-77h3PYSEC-2021-79PYSEC-2026-2961PYSEC-2026-2967

Published

May 21, 2021

Updated

Jul 13, 2026

Affected

3 pkgs

Patched

2 / 3

Exploits

None indexed

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs54th percentile — riskier than 54% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-33507 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

3 pkgs affected

🐍products-cmfcore🐍products-pluggableauthservice🐍plone

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Zope Products.CMFCore before 2.5.1 and Products.PluggableAuthService before 2.6.2, as used in Plone through 5.2.4 and other products, allow Reflected XSS.

Affected Packages

3 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`products-cmfcore`	all versions	2.5.1`pip install --upgrade 'products-cmfcore==2.5.1'`
🐍PyPI	`products-pluggableauthservice`	all versions	2.6.2`pip install --upgrade 'products-pluggableauthservice==2.6.2'`
🐍PyPI	`plone`	all versions	No fix

Affected Products

2 products · 3 configurations

Application

ploneplone

≥ 5.0 && ≤ 5.2.4

range

Application

zopezope

< 2.5.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for products-cmfcore, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update products-cmfcore to 2.5.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-33507 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

Zope Products.CMFCore before 2.5.1 and Products.PluggableAuthService before 2.6.2, as used in Plone through 5.2.4 and other products, allow Reflected XSS.

O3 Security · Impact-Aware SCA

Is CVE-2021-33507 in your dependencies?

Find it across PyPI, including transitive dependencies.

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CVSS Score

6.1/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Raw vector

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

CWE Classification

CWE-79Cross-site Scripting (XSS)

Weaponization

No known public exploit tooling found.

Timeline

Disclosed

May 21, 2021

Last updated

Jul 13, 2026

Identifiers

CVE-2021-33507

GHSA-35rg-466w-77h3

PYSEC-2021-79

PYSEC-2026-2961

PYSEC-2026-2967

References

Advisoryopenwall.com Advisoryplone.org Advisorynvd.nist.gov Advisorygithub.com Webgithub.com

Related vulnerabilities

Also affects plone

This CVE is medium severity, in line with the other 4 CVEs affecting plone.

CVE-2021-29002CVE-2011-1340CVE-2008-1396CVE-2006-1711

Same weakness: CWE-79

This CVE is medium severity; 4 of 4 other CVEs with CWE-79 are rated as high or higher (top: high).

CVE-2026-91127CVE-2026-77606CVE-2026-84992CVE-2026-77608Browse all CWE-79

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedJul 13, 2026