TYPO3 CMS - Broken Access Control in Backend and Install Tool

### Problem The referrer enforcement introduced with [TYPO3-CORE-SA-2020-006](https://news.typo3.com/security/advisory/typo3-core-sa-2020-006) ([CVE-2020-11069](https://www.cve.org/CVERecord?id=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. Source Code Location: https://github.com/TYPO3/typo3 Affected Packages: - composer:typo3/cms-backend, affected >= 13.0.0, < 13.4.34, patched in 13.4.34 - composer:typo3/cms-core, affected >= 14.0.0, < 14.3.6, patched in 14.3.6 CWEs: - CWE-346: Origin Validation Error - CWE-352: Cross-Site Request Forgery (CSRF) CVSS: - CVSS_V4: score 7.3, CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N References: - https://github.com/TYPO3/typo3/security/advisories/GHSA-68jx-f42c-7599 - https://nvd.nist.gov/vuln/detail/CVE-2026-19418 - https://github.com/TYPO3/typo3/commit/4a75e862c589c85d795d7c65dcdc835f8f413efc - https://github.com/TYPO3/typo3/commit/a0e8ee06a40e959b9e7b06a4b1cb19d3a0d3dcf7 - https://github.com/TYPO3/typo3/commit/ae0abd329d52285fe6e92804c3608820ad45e872 - https://github.com/FriendsOfPHP/security-advisories/blob/master/typo3/cms-core/CVE-2026-19418.yaml - https://news.typo3.com/security/advisory/typo3-core-sa-2026-021 - https://typo3.org/security/advisory/typo3-core-sa-2020-006 - https://typo3.org/security/advisory/typo3-core-sa-2026-021 - https://github.com/advisories/GHSA-68jx-f42c-7599