Open WebUI Channel Membership Authorization Bypass Vulnerability

A vulnerability exists in Open WebUI versions prior to 0.9.0, allowing deactivated users to retain full access to group and direct message channels. The issue arises because the 'is_user_channel_member' function fails to check the 'is_active' field of the 'ChannelMember' row. When a user is deactivated, their membership status is not updated to reflect this change, enabling continued read and write access to the channel via direct API calls. This flaw undermines the deactivation mechanism, creating a false sense of security for channel owners.

Impact

Exploitation of this vulnerability allows deactivated users to read messages in channels they should no longer access and to post, edit, and delete messages, creating a breach of trust in the channel management process.

Reproduction

To reproduce this vulnerability, a user must first be a member of a private group channel. Once they are a member, the channel owner can remove them, or they can leave voluntarily. After deactivation, the channel will no longer appear in the user's channel list, but the user can still access the channel's ID through previous messages or API calls. By using the direct API to access the channel's messages or to post, edit, or delete messages, the user can bypass the deactivation and manipulate the channel as if they were still an active member.

Remediation

Users are advised to update to Open WebUI version 0.9.0 or later, where this vulnerability has been fixed.