What is CVE-2021-33510?

CVE-2021-33510 is a medium-severity vulnerability in Plone, classified under Server-Side Request Forgery (SSRF). CVSS score: 4.3/10. Published 2021-05-21.

How severe is CVE-2021-33510?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Is CVE-2021-33510 known to be exploited?

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

SSRF in Plone

CVE-2021-33510

Plone through 5.2.4 allows remote authenticated managers to conduct SSRF attacks via an event ical URL, to read one line of a file.

Vulnerability class: SSRF (Server-Side Request Forgery)

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

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.010 (60.1th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 60th percentile — 60.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.010 · newest: 0.010 · 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-event-ical-u… (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-2021-33510?: CVE-2021-33510 is a medium-severity vulnerability in Plone, classified under Server-Side Request Forgery (SSRF). CVSS score: 4.3/10. Published 2021-05-21.
How severe is CVE-2021-33510?: Medium severity. CVSS v3 base score is 4.3 out of 10.
Is CVE-2021-33510 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.