GHSA-42wq-rch8-6f6j — @ckeditor/ckeditor5-markd…
MEDIUMGHSA-42wq-rch8-6f6j is a medium-severity (CVSS 5.8) Cross-site Scripting (XSS) vulnerability in @ckeditor/ckeditor5-markdown-gfm. A fix is available for @ckeditor/ckeditor5-markdown-gfm — see the affected versions and patch details below.
CKEditor5 cross-site scripting vulnerability caused by the editor instance destroying process
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-42wq-rch8-6f6j.
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.
How urgent is this, really
GHSA-42wq-rch8-6f6j plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@ckeditor/ckeditor5-markdown-gfmnpm@ckeditor/ckeditor5-html-supportnpm@ckeditor/ckeditor5-html-embednpmDescription
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 | 35.0.1npm install @ckeditor/ckeditor5-markdown-gfm@35.0.1 |
| 📦npm | @ckeditor/ckeditor5-html-support | all versions | 35.0.1npm install @ckeditor/ckeditor5-html-support@35.0.1 |
| 📦npm | @ckeditor/ckeditor5-html-embed | all versions | 35.0.1npm install @ckeditor/ckeditor5-html-embed@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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-42wq-rch8-6f6j can be triaged on real exposure rather than presence alone.
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 Security finds GHSA-42wq-rch8-6f6j across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.