Backend API configuration using Page TSconfig is vulnerable to arbitrary code execution and cross-site scripting. TSconfig fields of page properties in backend forms can be used to inject malicious sequences. Field tsconfig_includes is vulnerable to directory traversal leading to same scenarios as having direct access to TSconfig settings.

A valid backend user account having access to modify values for fields pages.TSconfig and pages.tsconfig_includes is needed in order to exploit this vulnerability.

References

• https://github.com/FriendsOfPHP/security-advisories/blob/master/typo3/cms/2019-06-25-4.yaml
• https://typo3.org/security/advisory/typo3-core-sa-2019-019