All XML processing within the TYPO3 CMS are vulnerable to XEE processing. This can lead to load internal and/or external (file) content within an XML structure. Furthermore it is possible to inject arbitrary files for an XML Denial of Service attack. For more information on that topic see https://www.owasp.org/index.php/XML_External_Entity_(XXE)_Processing.

References

• https://github.com/FriendsOfPHP/security-advisories/blob/master/typo3/cms/2016-02-23-1.yaml
• https://typo3.org/security/advisory/typo3-core-sa-2016-005