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TYPO3CMS

CVE-2021-21357

HIGH · 8.3 CVSS v3.1 Published 2021-03-23
Fix available
A fix is available. Upgrade to 8.7.40 / 9.5.25 or later.
See remediation →
89/100
Remediation priority · High
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
TYPO3 is an open source PHP based web content management system. In TYPO3 before versions 8.7.40, 9.5.25, 10.4.14, 11.1.1 due to improper input validation, attackers can by-pass restrictions of predefined options and submit arbitrary data in the Form Designer backend module of the Form Framework. In the default configuration of the Form Framework this allows attackers to explicitly allow arbitrary mime-types for file uploads - however, default _fileDenyPattern_ successfully blocked files like _.htaccess_ or _malicious.php_. Besides that, attackers can persist those files in any writable directory of the corresponding TYPO3 installation. A valid backend user account with access to the form module is needed to exploit this vulnerability. This is fixed in versions 8.7.40, 9.5.25, 10.4.14, 11.1.1.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In TYPO3 before versions 8.7.40, 9.5.25, 10.4.14, 11.1.1, the Form Designer backend module of the Form Framework has improper input validation that allows authenticated backend users to bypass predefined option restrictions and submit arbitrary data. This enables attackers to explicitly allow arbitrary mime-types for file uploads, potentially persisting malicious files in any writable directory of the TYPO3 installation.

MitigationUpgrade TYPO3 to version 8.7.40, 9.5.25, 10.4.14, or 11.1.1 or later. Additionally, review and restrict backend user permissions to the Form Framework module, and ensure fileDenyPattern configurations are properly applied.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
TYPO3CMS
Affected:>= 8.0.0, < 8.7.40>= 9.0.0, < 9.5.25>= 10.0.0, < 10.4.14>= 11.0.0, < 11.1.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Determine installed TYPO3 version
    Check the TYPO3 version via the backend admin panel (Help > About) or by inspecting the composer.json file in the web root for the 'typo3/cms' version entry
    Affected if The installed version falls within any of these ranges: >= 8.0.0 and < 8.7.40, >= 9.0.0 and < 9.5.25, >= 10.0.0 and < 10.4.14, or >= 11.0.0 and < 11.1.1
  2. Verify Form Designer module is accessible
    Log into the TYPO3 backend and navigate to the Form Designer module (typically under Web > Forms or the dedicated Form module), or check for the existence of form configuration files in the typo3conf or config directories
    Affected if The Form Designer module exists and is accessible to backend users in the installation
  3. Review backend user group permissions for Forms
    In TYPO3 backend, go to User Management > Access Lists or the permissions section for backend user groups, and verify whether the Form Framework or Form Designer module access is granted to any user group
    Affected if Any backend user group has explicit access or permissions granted to use the Form Designer/Form Framework module
  4. Inspect file upload restrictions
    Check the TYPO3 install tool or LocalConfiguration.php for the $GLOBALS['TYPO3_CONF_VARS']['BE']['fileDenyPattern'] setting, and review form element configurations for allowedMimeTypes settings in any form definitions
    Affected if The fileDenyPattern is not properly configured to deny dangerous file types, or custom mime-type allowances exist in form configurations that could allow executable files

The environment is affected if TYPO3 version is within the vulnerable ranges AND the Form Designer module is accessible to backend users with permissions that can be exploited to bypass mime-type restrictions.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Upgrade available Upgrade to 8.7.40 / 9.5.25 / 10.4.14 or later
Fixed in 8.7.409.5.2510.4.14
Interim mitigation

Upgrade TYPO3 to version 8.7.40, 9.5.25, 10.4.14, or 11.1.1 or later. Additionally, review and restrict backend user permissions to the Form Framework module, and ensure fileDenyPattern configurations are properly applied.

Fix this in TYPO3 Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-21357 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data