--- title: "TYPO3-CORE-SA-2021-005: Denial of Service in Page Error Handling" url: "https://news.typo3.com/security/advisory/typo3-core-sa-2021-005" description: It has been discovered that TYPO3 CMS is susceptible to denial of service. image: "https://news.typo3.com/_assets/d1e01514e4c4a5b3147940fa2ec50682/Images/og-image-news.jpg" date: 2026-06-11 modified: 2026-06-11 categories: - "Developer & Technology" - "Product Updates & Roadmap" - TYPO3 CMS --- # TYPO3-CORE-SA-2021-005: Denial of Service in Page Error Handling - [Developer & Technology](https://news.typo3.com/article/category/developer-technology) - [Product Updates & Roadmap](https://news.typo3.com/article/category/product-updates-roadmap) - Security / [TYPO3 CMS](https://news.typo3.com/article/category/security/typo3-cms) TYPO3-CORE-SA-2021-005: Denial of Service in Page Error Handling ================================================================ 16 March 2021 ![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 denial of service. - ![](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:** Page Error Handling (ext:core, ext:frontend) - **Release Date:** March 16, 2021 - **Vulnerability Type:** Denial of Service - **Affected Versions:** 9.0.0-9.5.24, 10.0.0-10.4.13, 11.0.0-11.1.0 - **Severity:** Medium - **Suggested CVSS:** [CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H/E:F/RL:O/RC:C](https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H/E:F/RL:O/RC:C&version=3.1) - **References:** [CVE-2021-21359](https://nvd.nist.gov/vuln/detail/CVE-2021-21359), [CWE-405](https://cwe.mitre.org/data/definitions/405.html), [CWE-674](https://cwe.mitre.org/data/definitions/674.html) ### Problem Description Requesting invalid or non-existing resources via HTTP triggers the page error handler which again could retrieve content  to be shown as an error message from another page. This leads to a scenario in which the application is calling itself recursively - amplifying the impact of the initial attack until the limits of the web server are exceeded. ### Solution Update to TYPO3 versions 9.5.25, 10.4.14, 11.1.1 that fix the problem described. ### Credits Thanks to Paul Keller, Mathias Bolt Lesniak and Kay Strobach who reported this issue and to TYPO3 framework merger Frank Nägler and to TYPO3 security team member Torben Hansen who fixed the issue. ### General Advice Follow the recommendations that are given in the [TYPO3 Security Guide](https://docs.typo3.org/typo3cms/CoreApiReference/Security/Index.html#security). Please subscribe to the [typo3-announce](http://lists.typo3.org/cgi-bin/mailman/listinfo/typo3-announce) mailing list. ### General Note All security related code changes are tagged so that 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)