TYPO3 CMS - Broken Access Control in Backend and Install Tool

Problem

The referrer enforcement introduced with TYPO3-CORE-SA-2020-006 (CVE-2020-11069) became ineffective in TYPO3 v13.0, where TYPO3 CMS started serving the backend and Admin Tool applications from the site's main entry script instead of the dedicated typo3/ directory.

Whether a request originated from the backend or Install Tool itself was determined by comparing the referrer against the directory of the entry script, which since then is the site root. As a consequence, requests originating from any script running on one of the TYPO3 instance's own domains, such as a frontend page, were accepted by backend routes and Install Tool endpoints.

Attackers able to execute JavaScript on one of those domains, for instance by exploiting a cross-site scripting vulnerability, could invoke these endpoints via Fetch/XHR with the privileges of an authenticated victim's user session.

Solution

Update to TYPO3 versions 13.4.34 LTS, 14.3.6 LTS that fix the problem described.

Credits

Thanks to Hổ Cao Từ for reporting this issue, and to TYPO3 core & security team member Benjamin Franzke for fixing it.