OpenProject is open-source, web-based project management software. Prior to 17.4.0, the GET /api/v3/relations endpoint allows any authenticated user to retrieve relations — and the subject (title) of work packages they have no permission to view — by supplying an arbitrary work package ID in the involved, fromId, or toId filter. This bypasses the Relation.visible scope due to a flawed performance optimization in RelationQuery. This vulnerability is fixed in 17.4.0.