Unrestricted File Upload in Form Framework

Exploitation

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

CVSS

8.0 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L/E:F/RL:O/RC:C

EPSS

• CVE-2021-21355: 1.63% estimated exploitation activity in the next 30 days; percentile 76.27 (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.

Problem Due to the lack of ensuring file extensions belong to configured allowed mime-types, attackers can upload arbitrary data with arbitrary file extensions - however, default fileDenyPattern successfully blocked files like .htaccess or malicious.php. TYPO3 Extbase extensions, which implement a file upload and do not implement a custom TypeConverter to transform uploaded files into FileReference domain model objects are affected by the vulnerability as well, since the UploadedFileReferenceConverter of ext:form handles the file upload and will accept files of any mime-type which are persisted to the default location. In any way, uploaded files are placed in the default location /fileadmin/userupload/, in most scenarios keeping the submitted filename - which allows attackers to directly reference files, or even correctly guess filenames used by other individuals, disclosing this information. No authentication is required to exploit this vulnerability. Solution Update to TYPO3…

Published by the source

23 Mar 2021, 01:53 UTC

Last modified by the source

2 Feb 2024, 16:44 UTC

Source last checked

26 Oct 2026, 14:15 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-2r6j-862c-m2v2

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# Patch Next advisory brief: CVE-2021-21355

Advisory: Unrestricted File Upload in Form Framework
IDs: CVE-2021-21355, GHSA-2r6j-862c-m2v2
Record: https://patchnext.com/advisories/cve-2021-21355 (revision 1, source checked 26 Oct 2026, 14:15 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.0)
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; typo3/cms-form 11.1.1, 10.4.14, 9.5.25, 8.7.40. 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
- Packagist typo3/cms-form: affected >= 8.0.0, <= 8.7.39; >= 9.0.0, <= 9.5.24; >= 10.0.0, <= 10.4.13; >= 11.0.0, <= 11.1.0; fixed in 10.4.14, 9.5.25, 8.7.40, 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.
- Packagist typo3/cms-form: 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, typo3/cms-form.
- 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-2r6j-862c-m2v2 (GitHub-reviewed advisory GHSA-2r6j-862c-m2v2 lists affected ranges: Packagist typo3/cms-form >=8.0.0 =9.0.0 =10.0.0 =11.0.0 =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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