TYPO3 is an open source PHP based web content management system. Versions prior to 9.5.38, 10.4.33, 11.5.20, and 12.1.1 are subject to Sensitive Information Disclosure. Due to the lack of handling user-submitted YAML placeholder expressions in the site configuration backend module, attackers could expose sensitive internal information, such as system configuration or HTTP request messages of other website visitors. A valid backend user account having administrator privileges is needed to exploit this vulnerability. This issue has been patched in versions 9.5.38 ELTS, 10.4.33, 11.5.20, 12.1.1.