It has been discovered that backend users having limited access to specific languages are capable of modifying and creating pages in the default language which actually should be disallowed. A valid backend user account is needed in order to exploit this vulnerability.

References

• TYPO3-CMS/core@64b1b5d
• https://github.com/FriendsOfPHP/security-advisories/blob/master/typo3/cms-core/2019-01-22-3.yaml
• https://typo3.org/security/advisory/typo3-core-sa-2019-003