typo3 -- Missing access check in Extbase

TYPO3 reports:

Extbase request handling fails to implement a proper access check for
requested controller/ action combinations, which makes it possible for an
attacker to execute arbitrary Extbase actions by crafting a special request. To
successfully exploit this vulnerability, an attacker must have access to at
least one Extbase plugin or module action in a TYPO3 installation. The missing
access check inevitably leads to information disclosure or remote code
execution, depending on the action that an attacker is able to execute.