GHSA-3wgj-c2hg-vm6q

# Summary When a user signs in via OAuth, Open WebUI fetches the `picture` claim URL, infers a MIME type from the URL extension via `mimetypes.guess_type`, and stores `data:<mime>;base64,...` as the user's profile image. The OAuth code path does not go through the `validate_profile_image_url` Pydantic validator that normally restricts profile images to PNG/JPEG/GIF/WebP. A `.svg` URL in the `picture` claim lands in the database as `data:image/svg+xml;base64,...`. The profile image endpoint `GET /api/v1/users/{id}/profile/image` returns the stored data URI with the attacker-controlled MIME type as `Content-Type` and `Content-Disposition: inline`. Security headers (CSP, `X-Content-Type-Options`) are env-gated and not set by default. An authenticated user navigating directly to that URL gets the SVG as a top-level document, executing `<script>`/`onload` in the same origin and able to read `localStorage.token` → account takeover. Same class of trust-boundary error as CVE-2025-64496 (trust of untrusted model servers) and CVE-2025-64495 (rich-text XSS). Different sink, different code path. # Details ## 1. MIME inferred from URL extension, not Content-Type `backend/open_webui/utils/oauth.py:1336-1345` — `_process_picture_url`: ```python response = await client.get(picture_url, ...) if response.status_code == 200: picture = response.content base64_encoded_picture = base64.b64encode(picture).decode("utf-8") guessed_mime_type = mimetypes.guess_type(picture_url)[0] if guessed_mime_type is None: guessed_mime_type = "image/jpeg" return f"data:{guessed_mime_type};base64,{base64_encoded_picture}" ``` No MIME allowlist. The upstream `Content-Type` is ignored. For a URL ending in `.svg`, `mimetypes.guess_type` returns `image/svg+xml`. ## 2. OAuth path bypasses the profile-image validator `backend/open_webui/utils/validate.py:10-36` defines `validate_profile_image_url`, which only accepts `/user.png`, `/user-mono.png`, and `data:image/{png,jpeg,g