TYPO3-CORE-SA-2021-005: Denial of Service in Page Error Handling

Categories: Development, TYPO3 CMS Created by Oliver Hader
It has been discovered that TYPO3 CMS is susceptible to denial of service.

Problem Description

Requesting invalid or non-existing resources via HTTP triggers the page error handler which again could retrieve content  to be shown as an error message from another page. This leads to a scenario in which the application is calling itself recursively - amplifying the impact of the initial attack until the limits of the web server are exceeded.


Update to TYPO3 versions 9.5.25, 10.4.14, 11.1.1 that fix the problem described.


Thanks to Paul Keller, Mathias Bolt Lesniak and Kay Strobach who reported this issue and to TYPO3 framework merger Frank Nägler and to TYPO3 security team member Torben Hansen who 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.