CVE-2021-21359

Meta

• 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 (5.5)
• CWE-405, CWE-674
• Status: DRAFT

Problem

Requesting invalid or non-existing resources via HTTP triggers the page error handler which again could retrieve content to be shown as 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.

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.

References

• TYPO3-CORE-SA-2021-005

CVE-2021-21359 has a CVSS score of 5.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (10.4.14, 11.1.1, 9.5.25); upgrading removes the vulnerable code path.

Kodem intelligence

Update to TYPO3 versions 9.5.25, 10.4.14, 11.1.1 that fix the problem described.

1. What is CVE-2021-21359? CVE-2021-21359 is a medium-severity security vulnerability in typo3/cms-core (composer), affecting versions >= 10.0.0, < 10.4.14. It is fixed in 10.4.14, 11.1.1, 9.5.25.
2. How severe is CVE-2021-21359? CVE-2021-21359 has a CVSS score of 5.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2021-21359?
   • typo3/cms-core (composer) (versions >= 10.0.0, < 10.4.14)
   • typo3/cms (composer) (versions >= 10.0.0, < 10.4.14)
4. Is there a fix for CVE-2021-21359? Yes. CVE-2021-21359 is fixed in 10.4.14, 11.1.1, 9.5.25. Upgrade to this version or later.
5. Is CVE-2021-21359 exploitable, and should I be worried? Whether CVE-2021-21359 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2021-21359 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2021-21359?
   • Upgrade typo3/cms-core to 10.4.14 or later
   • Upgrade typo3/cms-core to 11.1.1 or later
   • Upgrade typo3/cms-core to 9.5.25 or later
   • Upgrade typo3/cms to 10.4.14 or later
   • Upgrade typo3/cms to 11.1.1 or later
   • Upgrade typo3/cms to 9.5.25 or later