TYPO3 is an open source PHP based web content management system. Versions 9.0.0 through 9.5.28, 10.0.0 through 10.4.17, and 11.0.0 through 11.3.0 have a cross-site scripting vulnerability. When error messages are not properly encoded, the components _QueryGenerator_ and _QueryView_ are vulnerable to both reflected and persistent cross-site scripting. A valid backend user account having administrator privileges is needed to exploit this vulnerability. TYPO3 versions 9.5.29, 10.4.18, 11.3.1 contain a patch for this issue.