Mattermost versions prior to 8.0.0-20250815165020-c8d66301415d and 5.3.2-0.20250815165020-c8d66301415d have a vulnerability where guest users can access the archived channel search API without proper restrictions. This allows discovery of archived public channels via the /api/v4/teams/{team_id}/channels/search_archived endpoint. The issue is fixed in the specified versions.