CVE-2021-21357 — typo3/cms-form
HIGHCVE-2021-21357 is a high-severity (CVSS 8.3) Improper Input Validation vulnerability in typo3/cms-form. A fix is available for typo3/cms-form — see the affected versions and patch details below.
Broken Access Control in Form Framework
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-21357 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
typo3/cms-form🐘typo3/cms-form🐘typo3/cms-form🐘typo3/cms-form🐘typo3/cms-core🐘typo3/cms-core🐘typo3/cms-core🐘typo3/cms+2 moreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
Problem
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.
Solution
Update to TYPO3 versions 8.7.40, 9.5.25, 10.4.14, 11.1.1 that fix the problem described.
Credits
Thanks to Richie Lee who reported this issue and to TYPO3 contributor Ralf Zimmermann who fixed the issue.
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | typo3/cms-form | ≥ 8.0.0&&< 8.7.40 | 8.7.40composer require typo3/cms-form:^8.7.40 |
| 🐘Packagist | typo3/cms-form | ≥ 9.0.0&&< 9.5.25 | 9.5.25composer require typo3/cms-form:^9.5.25 |
| 🐘Packagist | typo3/cms-form | ≥ 10.0.0&&< 10.4.14 | 10.4.14composer require typo3/cms-form:^10.4.14 |
| 🐘Packagist | typo3/cms-form | ≥ 11.0.0&&< 11.1.1 | 11.1.1composer require typo3/cms-form:^11.1.1 |
| 🐘Packagist | typo3/cms-core | ≥ 10.0.0&&< 10.4.14 | 10.4.14composer require typo3/cms-core:^10.4.14 |
| 🐘Packagist | typo3/cms-core | ≥ 11.0.0&&< 11.1.1 | 11.1.1composer require typo3/cms-core:^11.1.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for typo3/cms-form, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update typo3/cms-form to 8.7.40 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21357 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2021-21357 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2021-21357. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-21357 in your dependencies?
O3 Security finds CVE-2021-21357 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.