TYPO3 is an open source PHP based web content management system. In versions prior to 9.5.38, 10.4.33, 11.5.20, and 12.1.1, 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 very similar, but not identical, to the one described in CVE-2021-21359. This issue is patched in versions 9.5.38 ELTS, 10.4.33, 11.5.20 or 12.1.1.