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Medium, CVSS 6.1amended

md-editor-v3: XSS via fenced-code language rendering bypass

CVE-2026-84992GHSA-3rm2-h79c-8qw6

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (md-editor-v3 6.5.4), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
6.1 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
EPSS
  • CVE-2026-84992: 0.33% estimated exploitation activity in the next 30 days; percentile 25.84 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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 htmlblock and htmlinline 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: x"<details/open/ontoggle=alert(document.domain)\nSAFE\n Create and run the app, replacing src/main.js when indicated:…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-3rm2-h79c-8qw6

  2. Revision 2 · amended ·

    Amended from osv record GHSA-3rm2-h79c-8qw6

  3. Revision 1 · created ·

    Published from ghsa record GHSA-3rm2-h79c-8qw6

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-84992

Advisory: md-editor-v3: XSS via fenced-code language rendering bypass
IDs: CVE-2026-84992, GHSA-3rm2-h79c-8qw6
Record: https://patchnext.com/advisories/cve-2026-84992 (revision 3, source checked 26 Oct 2026, 13:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: md-editor-v3 6.5.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm md-editor-v3: affected <= 6.5.3; fixed in 6.5.4

## Suggested inspection (read-only)
- `npm ls md-editor-v3 --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on md-editor-v3.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-3rm2-h79c-8qw6 (GitHub-reviewed advisory GHSA-3rm2-h79c-8qw6 lists affected ranges: npm md-editor-v3 >=0 <=6.5.3)
- Verified: https://osv.dev/vulnerability/GHSA-3rm2-h79c-8qw6 (OSV record GHSA-3rm2-h79c-8qw6 lists affected ranges: npm md-editor-v3 >=0 <6.5.4 (fixed))

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