CVE-2026-28343
MEDIUMCVE-2026-28343 is a medium-severity (CVSS 6.4) Cross-site Scripting (XSS) vulnerability in @ckeditor/ckeditor5-html-support. O3 Security confirms whether CVE-2026-28343 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
CKEditor: Cross-site scripting (XSS) in the HTML Support package
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
ckeditor5npmDescription
CKEditor 5 is a modern JavaScript rich-text editor with an MVC architecture. Starting in version 29.0.0 and prior to version 47.6.0, a cross-site scripting (XSS) vulnerability has been discovered in the General HTML Support feature. This vulnerability could be triggered by inserting specially crafted markup, leading to unauthorized JavaScript code execution, if the editor instance used an unsafe General HTML Support configuration. This issue has been patched in version 47.6.0.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @ckeditor/ckeditor5-html-support | ≥ 29.0.0&&< 47.6.0 | 47.6.0 |
| 📦npm | ckeditor5 | ≥ 29.0.0&&< 47.6.0 | 47.6.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @ckeditor/ckeditor5-html-support. 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 @ckeditor/ckeditor5-html-support to 47.6.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-28343 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-2026-28343 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-2026-28343. 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-2026-28343 in your dependencies?
O3 detects CVE-2026-28343 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.