What is CVE-2021-21358?

CVE-2021-21358 is a medium-severity vulnerability in TYPO3, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2021-03-23.

How severe is CVE-2021-21358?

Medium severity. CVSS v3 base score is 5.4 out of 10.

XSS in TYPO3

CVE-2021-21358

TYPO3 is an open source PHP based web content management system. In TYPO3 before versions 10.4.14, 11.1.1 it has been discovered that the Form Designer backend module of the Form Framework is vulnerable to cross-site scripting. A valid backend user account with access to the form module is needed to exploit this vulnerability. This is fixed in versions 10.4.14, 11.1.1.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-03-23 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.009 (57.3th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 57th percentile — 57.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

TYPO3
TYPO3 Typo3.cms — versions >= 10.2.0, <= 10.4.13, >= 11.0.0, <= 11.1.0

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

github.com/TYPO3/TYPO3.CMS/security/advisories/GHSA-x79j-wgqv-g8h2 (Third Party Advisory)
packagist.org/packages/typo3/cms-form (Third Party Advisory, Release Notes)
typo3.org/security/advisory/typo3-core-sa-2021-004 (Vendor Advisory)

Frequently asked questions

What is CVE-2021-21358?: CVE-2021-21358 is a medium-severity vulnerability in TYPO3, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2021-03-23.
How severe is CVE-2021-21358?: Medium severity. CVSS v3 base score is 5.4 out of 10.