In TYPO3 installations with the "mediace" extension from version 7.6.2 and before version 7.6.5, it has been discovered that an internal verification mechanism can be used to generate arbitrary checksums. The allows to inject arbitrary data having a valid cryptographic message authentication code and can lead to remote code execution. To successfully exploit this vulnerability, an attacker must have access to at least one `Extbase` plugin or module action in a TYPO3 installation. This is fixed in version 7.6.5 of the "mediace" extension for TYPO3.