What is CVE-2021-33511?

CVE-2021-33511 is a high-severity vulnerability in Plone, classified under Server-Side Request Forgery (SSRF). CVSS score: 7.5/10. Published 2021-05-21.

How severe is CVE-2021-33511?

High severity. CVSS v3 base score is 7.5 out of 10.

Is CVE-2021-33511 known to be exploited?

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

SSRF in Plone

CVE-2021-33511

Plone though 5.2.4 allows SSRF via the lxml parser. This affects Diazo themes, Dexterity TTW schemas, and modeleditors in plone.app.theming, plone.app.dexterity, and plone.supermodel.

Vulnerability class: SSRF (Server-Side Request Forgery)

Published 2021-05-21 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.012 (65.8th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 66th percentile — 65.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.011 · newest: 0.012 · change: +0.000

Affected products

Plone

Weakness classification (CWE)

CWE-918 — Server-Side Request Forgery (SSRF)

Public proof-of-concept exploits

cyllective/CVEs

References

plone.org/security/hotfix/20210518/server-side-request-forgery-via-lxml-parser (Vendor Advisory)
www.openwall.com/lists/oss-security/2021/05/22/1 (mailing-list, Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2021-33511?: CVE-2021-33511 is a high-severity vulnerability in Plone, classified under Server-Side Request Forgery (SSRF). CVSS score: 7.5/10. Published 2021-05-21.
How severe is CVE-2021-33511?: High severity. CVSS v3 base score is 7.5 out of 10.
Is CVE-2021-33511 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.