GHSA-42wq-rch8-6f6j
MEDIUMCKEditor5 cross-site scripting vulnerability caused by the editor instance destroying process
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.
Blast Radius
@ckeditor/ckeditor5-markdown-gfm📦@ckeditor/ckeditor5-html-support📦@ckeditor/ckeditor5-html-embedReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.
Description
Affected packages
@ckeditor/ckeditor5-markdown-gfm @ckeditor/ckeditor5-html-support @ckeditor/ckeditor5-html-embed
Impact
A cross-site scripting vulnerability has been discovered affecting three optional CKEditor 5's packages. The vulnerability allowed to trigger a JavaScript code after fulfilling special conditions:
a) Using one of the affected packages. In case of ckeditor5-html-support and ckeditor5-html-embed, additionally, it was required to use a configuration that allows unsafe markup inside the editor,
b) Initializing the editor on an element and using an element other than <textarea> as a base,
c) Destroying the editor instance.
The root cause of the issue was a mechanism responsible for updating the source element with the markup coming from the CKEditor 5 data pipeline after destroying the editor.
This vulnerability might affect a small percent of integrators that depend on dynamic editor initialization/destroy and use Markdown, General HTML Support or HTML embed features.
Patches
The problem has been recognized and patched. The fix will be available in version 35.0.1.
For more information
Email us at [email protected] if you have any questions or comments about this advisory.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @ckeditor/ckeditor5-markdown-gfm | all versions | 35.0.1 |
| 📦npm | @ckeditor/ckeditor5-html-support | all versions | 35.0.1 |
| 📦npm | @ckeditor/ckeditor5-html-embed | all versions | 35.0.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @ckeditor/ckeditor5-markdown-gfm. 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-markdown-gfm to 35.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-42wq-rch8-6f6j 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-42wq-rch8-6f6j 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-42wq-rch8-6f6j. 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-42wq-rch8-6f6j in your dependencies?
O3 detects GHSA-42wq-rch8-6f6j across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.