--- title: "TYPO3-CORE-SA-2026-021: Broken Access Control in Backend and Install Tool" url: "https://news.typo3.com/security/advisory/typo3-core-sa-2026-021" description: It has been discovered that TYPO3 CMS is susceptible to broken access control. image: "https://news.typo3.com/_assets/d1e01514e4c4a5b3147940fa2ec50682/Images/og-image-news.jpg" date: 2026-08-11 modified: 2026-08-25 categories: - TYPO3 CMS --- # TYPO3-CORE-SA-2026-021: Broken Access Control in Backend and Install Tool - Security / [TYPO3 CMS](https://news.typo3.com/article/category/security/typo3-cms) TYPO3-CORE-SA-2026-021: Broken Access Control in Backend and Install Tool ========================================================================= 11 August 2026 ![A laptop screen displaying a list of security advisories](https://news.typo3.com/typo3temp/assets/_processed_/d/c/csm_security_blog_default_77f8e86036.webp) It has been discovered that TYPO3 CMS is susceptible to broken access control. - ![](https://news.typo3.com/typo3temp/assets/t3g/blog/gravatar/b8266fdc667b773926c59081862ab148.jpeg)[Oliver Hader](https://news.typo3.com/article/author/oliver-hader) --- - **Component Type:** TYPO3 CMS - **Subcomponent:** Backend & Admin Tool (ext:backend, ext:install) - **Release Date:** August 11, 2026 - **Vulnerability Type:** Broken Access Control - **Affected Versions:** 13.0.0-13.4.33, 14.0.0-14.3.5 - **Severity:** High - **Suggested CVSS:** [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](https://vulnogram.org/cvss4?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:** [ CVE-2026-19418](https://www.cve.org/CVERecord?id=%20CVE-2026-19418), [CWE-346](https://cwe.mitre.org/data/definitions/346.html), [CWE-352](https://cwe.mitre.org/data/definitions/352.html) --- ### Problem Description 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. ### General Advice Follow the recommendations that are given in the [TYPO3 Security Guide](https://docs.typo3.org/m/typo3/reference-coreapi/main/en-us/Security/Index.html). Please subscribe to the [typo3-announce](https://lists.typo3.org/pipermail/typo3-announce/) mailing list. ### General Note All security-related code changes are tagged so you can easily look them up in our [review system](https://review.typo3.org/#/q/status:merged+project:Packages/TYPO3.CMS+topic:security,n,z). ![](https://news.typo3.com/typo3temp/assets/t3g/blog/gravatar/cc7cba9757f98fbe05023a139119df74.jpeg) About the Author [Oliver Hader](https://news.typo3.com/article/author/oliver-hader) Core Developer at TYPO3 GmbH,Hof, Germany [Website](https://typo3.com)[Twitter](https://twitter.com/ohader)[LinkedIn](https://www.linkedin.com/in/oliverhader/)[Xing](https://www.xing.com/profile/Oliver_Hader) Oliver started to work with TYPO3 in 2005 and was fascinated by the product and its universe. Since 2007 he is member of the TYPO3 Core Team. After going back to university in 2014 for achieving a postgraduate master degree in internet web science, he is now researching on advanced web technology topics in general and for TYPO3 in particular. In his spare time, Oliver loves to go cycling cross-country in the uplands around Hof (Germany) in northern Bavaria - at the region where he's living as well. [More posts by this author](https://news.typo3.com/article/author/oliver-hader)