relay_crypt(circuit_t *circ, cell_t *cell, cell_direction_t cell_direction,
            crypt_path_t **layer_hint, char *recognized)
{
  relay_header_t rh;

  tor_assert(circ);
  tor_assert(cell);
  tor_assert(recognized);
  tor_assert(cell_direction == CELL_DIRECTION_IN ||
             cell_direction == CELL_DIRECTION_OUT);

  if (cell_direction == CELL_DIRECTION_IN) {
    if (CIRCUIT_IS_ORIGIN(circ)) { /* We're at the beginning of the circuit.
                                    * We'll want to do layered decrypts. */
      crypt_path_t *thishop, *cpath = TO_ORIGIN_CIRCUIT(circ)->cpath;
      thishop = cpath;
      if (thishop->state != CPATH_STATE_OPEN) {
        log_fn(LOG_PROTOCOL_WARN, LD_PROTOCOL,
               "Relay cell before first created cell? Closing.");
        return -1;
      }
      do { /* Remember: cpath is in forward order, that is, first hop first. */
        tor_assert(thishop);

        if (relay_crypt_one_payload(thishop->b_crypto, cell->payload, 0) < 0)
          return -1;

        relay_header_unpack(&rh, cell->payload);
        if (rh.recognized == 0) {
          /* it's possibly recognized. have to check digest to be sure. */
          if (relay_digest_matches(thishop->b_digest, cell)) {
            *recognized = 1;
            *layer_hint = thishop;
            return 0;
          }
        }

        thishop = thishop->next;
      } while (thishop != cpath && thishop->state == CPATH_STATE_OPEN);
      log_fn(LOG_PROTOCOL_WARN, LD_OR,
             "Incoming cell at client not recognized. Closing.");
      return -1;
    } else { /* we're in the middle. Just one crypt. */
      if (relay_crypt_one_payload(TO_OR_CIRCUIT(circ)->p_crypto,
                                  cell->payload, 1) < 0)
        return -1;
    }
  } else /* cell_direction == CELL_DIRECTION_OUT */ {
    /* we're in the middle. Just one crypt. */

    if (relay_crypt_one_payload(TO_OR_CIRCUIT(circ)->n_crypto,
                                cell->payload, 0) < 0)
      return -1;

    relay_header_unpack(&rh, cell->payload);
    if (rh.recognized == 0) {
      /* it's possibly recognized. have to check digest to be sure. */
      if (relay_digest_matches(TO_OR_CIRCUIT(circ)->n_digest, cell)) {
        *recognized = 1;
        return 0;
      }
    }
  }
  return 0;
}

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.