Plane is an open-source project management tool. Prior to 1.4.0, GET /api/workspaces/{slug}/entity-search/?query_type=user_mention returns workspace-member display names, UUIDs, and avatar URLs to any authenticated user who knows the workspace slug, even when the caller is not a workspace member. The endpoint also exposes ProjectMember rows under the same condition. SearchEndpoint in apps/api/plane/app/views/search/base.py inherits BaseAPIView with only permission_classes = [IsAuthenticated] and performs no workspace-membership check. This issue is fixed in 1.4.0.