Capturability analysis of the linear inverted pendulum model (LIPM) enabled walking over even terrains based on the capture point. We generalize this analysis to the inverted pendulum model (IPM) and show how it enables 3D walking over uneven terrains based on capture inputs. Thanks to a tailored optimization scheme, we can compute these inputs fast enough for a real-time control loop. We implement this approach as open-source software and demonstrate it in simulations.