Vulnerability Description

In standard channels (i.e., channels whose channel.type is neither group nor dm), the endpoint

POST /api/v1/channels/{channel_id}/messages/{message_id}/update can be accessed with read permission only.

When access_control is set to None, the authorization check has_access(..., type="read") evaluates to True, allowing users who are not the message owner to update messages.

As a result, unauthorized modification of other users’ messages is possible.

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Attack Prerequisites

• The attacker is an authenticated user (role user or higher)
• The target channel is a standard channel (i.e., not group or dm)
• access_control is None or allows read access
• The attacker can obtain the target message_id (e.g., via the channel’s message list)

Attack Scenario

1. The attacker (User B) retrieves another user’s message_id from the message list in a standard channel

2. The attacker sends a request to

   POST /api/v1/channels/{channel_id}/messages/{message_id}/update

3. The message authored by another user (User A) is successfully updated

Potential Impact

• Unauthorized modification of other users’ messages (violation of data integrity)

Steps to Reproduce

1. Log in as an administrator

<img width="3334" height="1668" alt="image" src="https://github.com/user-attachments/assets/b20323d3-c050-4438-8912-193a417654bc" />

1. Create User A

<img width="3346" height="788" alt="image" src="https://github.com/user-attachments/assets/b9e4fb8a-b14e-4a4b-b012-02ccfba52fca" />

1. Create User B

<img width="3354" height="796" alt="image" src="https://github.com/user-attachments/assets/f3cf6892-e6c9-4778-b471-f1cc0deec6c8" />

1. Log in as User A

<img width="3360" height="1668" alt="image" src="https://github.com/user-attachments/assets/5264ee07-f5c5-4bbe-ad4f-da69fb540fc9" />

1. Log in as User B

<img width="3354" height="1670" alt="image" src="https://github.com/user-attachments/assets/f112f8e8-b3e2-4e65-b226-c7b6c986f3bb" />

1. As the administrator, create a new channel

<img width="2582" height="988" alt="image" src="https://github.com/user-attachments/assets/bc012d9a-f884-4c83-b6bb-d1e5399f61bb" />

1. As User A, post a new message in the channel

<img width="2626" height="962" alt="image" src="https://github.com/user-attachments/assets/d7ff12c2-fe17-44f0-aaf9-5ce2bac9a378" />

1. As User B, edit User A’s message

<img width="2604" height="958" alt="image" src="https://github.com/user-attachments/assets/8e19ec3e-fdda-4d36-acd5-f3e1fd3402dd" />

1. Confirm that User A’s message has been modified without authorization

<img width="2378" height="1976" alt="image" src="https://github.com/user-attachments/assets/6415fd41-ac68-4d42-83c9-6297caee1fb4" />

Affected Files and Line Numbers

• backend/open_webui/routers/channels.py:1417–1460

  The authorization check in update_message_by_id allows access with read permission

• backend/open_webui/utils/access_control.py:124–135

  When access_control=None and strict=True, read access is permitted

• backend/open_webui/models/messages.py:341–358

  The update logic does not enforce any message ownership check

Recommended Mitigation

Update the condition in

backend/open_webui/routers/channels.py:1451–1456

by changing the permission check from read to write, so that only administrators, message owners, or users with write permission can update messages.

Proposed Changes

• For standard channels, change the update permission requirement from

  has_access(..., type="read") to has_access(..., type="write")

• Preserve the existing ownership check (message.user_id == user.id)

AI Usage

• Translation from Japanese to English
• CWE classification and assessment
• Affected Files and Line Numbers