GHSA-c5c9-8c6m-727v
MEDIUMGHSA-c5c9-8c6m-727v is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in typo3/cms-core. O3 Security confirms whether GHSA-c5c9-8c6m-727v is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Cross-Site Scripting via Rich-Text Content
Real-World Exposure
typo3/cms-core🐘typo3/cms-core🐘typo3/cms-core🐘typo3/cms-core🐘typo3/cms-core🐘typo3/cms🐘typo3/cms🐘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
Meta
- CVSS:
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N/E:F/RL:O/RC(5.7)
Problem
Failing to properly parse, sanitize and encode malicious rich-text content, the content rendering process in the website frontend is vulnerable to cross-site scripting. Corresponding rendering instructions via TypoScript functionality HTMLparser do not consider all potentially malicious HTML tag & attribute combinations per default.
In addition, the lack of comprehensive default node configuration for rich-text fields in the backend user interface fosters this malfunction.
In default scenarios, a valid backend user account is needed to exploit this vulnerability. In case custom plugins used in the website frontend accept and reflect rich-text content submitted by users, no authentication is required.
Solution
Update to TYPO3 versions 7.6.53 ELTS, 8.7.42 ELTS, 9.5.29, 10.4.19, 11.3.2 that fix the problem described above.
Custom package typo3/html-sanitizer - based on allow-lists only - takes care of sanitizing potentially malicious markup. The default behavior is based on safe and commonly used markup - however, this can be extended or restricted further in case it is necessary for individual scenarios.
During the frontend rendering process, sanitization is applied to the default TypoScript path lib.parseFunc, which is implicitly used by the Fluid view-helper instruction f:format.html. Rich-text data persisted using the backend user interface is sanitized as well. Implementation details are explained in corresponding ChangeLog documentation.
Credits
Thanks to Benjamin Stiber, Gert-Jan Jansma, Gábor Ács-Kurucz, Alexander Kellner, Richie Lee, Nina Rösch who reported this issue, and to TYPO3 security team member Oliver Hader, as well as TYPO3 contributor Susanne Moog who fixed the issue.
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | typo3/cms-core | ≥ 7.0.0&&< 7.6.53 | 7.6.53 |
| 🐘Packagist | typo3/cms-core | ≥ 8.0.0&&< 8.7.42 | 8.7.42 |
| 🐘Packagist | typo3/cms-core | ≥ 10.0.0&&< 10.4.19 | 10.4.19 |
| 🐘Packagist | typo3/cms-core | ≥ 11.0.0&&< 11.3.2 | 11.3.2 |
| 🐘Packagist | typo3/cms-core | ≥ 9.0.0&&< 9.5.29 | 9.5.29 |
| 🐘Packagist | typo3/cms | ≥ 10.0.0&&< 10.4.19 | 10.4.19 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for typo3/cms-core. 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-core to 7.6.53 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-c5c9-8c6m-727v 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 GHSA-c5c9-8c6m-727v 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 GHSA-c5c9-8c6m-727v. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-c5c9-8c6m-727v in your dependencies?
O3 detects GHSA-c5c9-8c6m-727v across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.