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

2. Create User A

3. Create User B

4. Log in as User A

5. Log in as User B

6. As the administrator, create a new channel

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

8. As User B, edit User A’s message

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

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