GHSA-4fc4-4p5g-6w89
MEDIUMGHSA-4fc4-4p5g-6w89 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in ckeditor4. O3 Security confirms whether GHSA-4fc4-4p5g-6w89 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Cross-site Scripting in CKEditor4
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
ckeditor4npmDescription
Affected packages
The vulnerability has been discovered in the core HTML processing module and may affect all plugins used by CKEditor 4.
Impact
A potential vulnerability has been discovered in CKEditor 4 HTML processing core module. The vulnerability allowed to inject malformed HTML bypassing content sanitization, which could result in executing JavaScript code. It affects all users using the CKEditor 4 at version < 4.18.0.
Patches
The problem has been recognized and patched. The fix will be available in version 4.18.0.
For more information
Email us at [email protected] if you have any questions or comments about this advisory.
Acknowledgements
The CKEditor 4 team would like to thank GHSL team member Kevin Backhouse (@kevinbackhouse) for recognizing and reporting this vulnerability.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | ckeditor4 | all versions | 4.18.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for ckeditor4. 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 ckeditor4 to 4.18.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-4fc4-4p5g-6w89 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-4fc4-4p5g-6w89 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-4fc4-4p5g-6w89. 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-4fc4-4p5g-6w89 in your dependencies?
O3 detects GHSA-4fc4-4p5g-6w89 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.