Mahara before 1.5.12, 1.6.x before 1.6.7, and 1.7.x before 1.7.3 does not properly restrict access to artefacts, which allows remote authenticated users to read arbitrary artefacts via the (1) artefact id in an upload action when creating a journal or (2) instconf_artefactid_selected[ID] parameter in an upload action when editing a block.