Denial of Service in Page Error Handling

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.5 · 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

EPSS

• CVE-2021-21359: 1.73% estimated exploitation activity in the next 30 days; percentile 77.65 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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. 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. References TYPO3-CORE-SA-2021-005

Published by the source

23 Mar 2021, 01:54 UTC

Last modified by the source

7 Feb 2024, 18:50 UTC

Source last checked

26 Oct 2026, 14:16 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-4p9g-qgx9-397p

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# Patch Next advisory brief: CVE-2021-21359

Advisory: Denial of Service in Page Error Handling
IDs: CVE-2021-21359, GHSA-4p9g-qgx9-397p
Record: https://patchnext.com/advisories/cve-2021-21359 (revision 1, source checked 26 Oct 2026, 14:16 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: typo3/cms-core 11.1.1, 10.4.14, 9.5.25; typo3/cms 11.1.1, 10.4.14, 9.5.25. A vendor fix does not mean a deployment is fixed.

## Affected components
- Packagist typo3/cms-core: affected >= 10.0.0, < 10.4.14; >= 11.0.0, < 11.1.1; >= 9.0.0, < 9.5.25; fixed in 10.4.14, 9.5.25, 11.1.1
- Packagist typo3/cms: affected >= 10.0.0, < 10.4.14; >= 11.0.0, < 11.1.1; >= 9.0.0, < 9.5.25; fixed in 10.4.14, 9.5.25, 11.1.1

## Suggested inspection (read-only)
- Packagist typo3/cms-core: check the installed version with your package manager.
- Packagist typo3/cms: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on typo3/cms-core, typo3/cms.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-4p9g-qgx9-397p (GitHub-reviewed advisory GHSA-4p9g-qgx9-397p lists affected ranges: Packagist typo3/cms-core >=10.0.0 =11.0.0 =9.0.0 =10.0.0 =11.0.0 =9.0.0 <9.5.25)

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