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.

References

• https://github.com/FriendsOfPHP/security-advisories/blob/master/typo3/cms/2016-05-24-1.yaml
• https://web.archive.org/web/20160606110438/https://typo3.org/teamssecuritysecurity-bulletins/security-bulletins-single-view/article/missing-access-check-in-typo3-cms