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.

This vulnerability is the same as described in TYPO3-CORE-SA-2021-005 (CVE-2021-21359). A regression, introduced during TYPO3 v11 development, led to this situation.

Solution

Update to TYPO3 version 11.5.16 that fixes the problem described above.

Credits

Thanks to Rik Willems who reported this issue and to TYPO3 core & security team member Oliver Hader 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.