TYPO3-CORE-SA-2021-009: Cross-Site Scripting in Page Preview

Categories: Development Created by Oliver Hader
It has been discovered that TYPO3 CMS is vulnerable to cross-site scripting.

Problem Description

Failing to properly encode Page TSconfig settings, the corresponding page preview module (Web>View) is vulnerable to persistent cross-site scripting. A valid backend user account is needed to exploit this vulnerability.


Update to TYPO3 versions 9.5.28, 10.4.18, 11.3.1 that fix the problem described.


Thanks to TYPO3 core merger Oliver Bartsch who reported and fixed the issue.

General Advice

Follow the recommendations that are given in the TYPO3 Security Guide. Please subscribe to the typo3-announce mailing list.

General Note

All security related code changes are tagged so that you can easily look them up in our review system.