relay_lookup_conn(circuit_t *circ, cell_t *cell,
                  cell_direction_t cell_direction, crypt_path_t *layer_hint)
{
  edge_connection_t *tmpconn;
  relay_header_t rh;

  relay_header_unpack(&rh, cell->payload);

  if (!rh.stream_id)
    return NULL;

  /* IN or OUT cells could have come from either direction, now
   * that we allow rendezvous *to* an OP.
   */

  if (CIRCUIT_IS_ORIGIN(circ)) {
    for (tmpconn = TO_ORIGIN_CIRCUIT(circ)->p_streams; tmpconn;
         tmpconn=tmpconn->next_stream) {
      if (rh.stream_id == tmpconn->stream_id &&
          !tmpconn->base_.marked_for_close &&
          tmpconn->cpath_layer == layer_hint) {
        log_debug(LD_APP,"found conn for stream %d.", rh.stream_id);
        return tmpconn;
      }
    }
  } else {
    for (tmpconn = TO_OR_CIRCUIT(circ)->n_streams; tmpconn;
         tmpconn=tmpconn->next_stream) {
      if (rh.stream_id == tmpconn->stream_id &&
          !tmpconn->base_.marked_for_close) {
        log_debug(LD_EXIT,"found conn for stream %d.", rh.stream_id);
        if (cell_direction == CELL_DIRECTION_OUT ||
            connection_edge_is_rendezvous_stream(tmpconn))
          return tmpconn;
      }
    }
    for (tmpconn = TO_OR_CIRCUIT(circ)->resolving_streams; tmpconn;
         tmpconn=tmpconn->next_stream) {
      if (rh.stream_id == tmpconn->stream_id &&
          !tmpconn->base_.marked_for_close) {
        log_debug(LD_EXIT,"found conn for stream %d.", rh.stream_id);
        return tmpconn;
      }
    }
  }
  return NULL; /* probably a begin relay cell */
}

The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.