CVE-2021-21358
MEDIUMCVE-2021-21358 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in typo3/cms-form. O3 Security confirms whether CVE-2021-21358 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in typo3/cms-form
Blast Radius
typo3/cms-form🐘typo3/cms-form🐘typo3/cms-core🐘typo3/cms-core🐘typo3/cms🐘typo3/cmsReal-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
TYPO3 is an open source PHP based web content management system. In TYPO3 before versions 10.4.14, 11.1.1 it has been discovered that the Form Designer backend module of the Form Framework is vulnerable to cross-site scripting. A valid backend user account with access to the form module is needed to exploit this vulnerability. This is fixed in versions 10.4.14, 11.1.1.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | typo3/cms-form | ≥ 10.2.0&&< 10.4.14 | 10.4.14 |
| 🐘Packagist | typo3/cms-form | ≥ 11.0.0&&< 11.1.1 | 11.1.1 |
| 🐘Packagist | typo3/cms-core | ≥ 10.0.0&&< 10.4.14 | 10.4.14 |
| 🐘Packagist | typo3/cms-core | ≥ 11.0.0&&< 11.1.1 | 11.1.1 |
| 🐘Packagist | typo3/cms | ≥ 10.0.0&&< 10.4.14 | 10.4.14 |
| 🐘Packagist | typo3/cms | ≥ 11.0.0&&< 11.1.1 | 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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update typo3/cms-form to 10.4.14 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21358 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 pinpoints whether CVE-2021-21358 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2021-21358. 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-2021-21358 in your dependencies?
O3 detects CVE-2021-21358 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.