GHSA-8wvc-869r-xfqf Open WebUI Vulnerable to Stored DOM XSS via Note 'Download PDF'

• npm open-webui: < 0.6.37 → fixed in 0.6.37

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: `token_stealer.md` ```markdown ``` > 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-s1ib_hIG4LayFw ``` And Simple PoC `alert(1)` Filename: `simple_poc.md` ```markdown ``` --- 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 ``` --- 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, { ALLOWED_TAGS: [ 'p', 'br', 'strong', 'em', 'u', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'ul', 'ol', 'li', 'a', 'code', 'pre', 'blockquote', 'table', 'thead', 'tbody', 'tr', 'td', 'th' ], ALLOWED_ATTR: ['href', 'class', 'target'], FORBID_TAGS: ['svg', 'script', 'iframe', 'object', 'embed', 'style'], FORBID_ATTR: ['onload', 'onerror', 'onclick', 'onmouseover', 'onfocus'], ALLOW_DATA_ATTR: false }); node.appendChild(contentNode); ``` --- References • OWASP XSS Prevention Cheat Sheet: https://cheatsheetseries.owasp.org/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.html • DOMPurify: https://github.com/cure53/DOMPurify ---