relay_digest_matches(crypto_digest_t *digest, cell_t *cell)
{
  char received_integrity[4], calculated_integrity[4];
  relay_header_t rh;
  crypto_digest_t *backup_digest=NULL;

  backup_digest = crypto_digest_dup(digest);

  relay_header_unpack(&rh, cell->payload);
  memcpy(received_integrity, rh.integrity, 4);
  memset(rh.integrity, 0, 4);
  relay_header_pack(cell->payload, &rh);


  crypto_digest_add_bytes(digest, (char*) cell->payload, CELL_PAYLOAD_SIZE);
  crypto_digest_get_digest(digest, calculated_integrity, 4);

  if (tor_memneq(received_integrity, calculated_integrity, 4)) {
    /* restore digest to its old form */
    crypto_digest_assign(digest, backup_digest);
    /* restore the relay header */
    memcpy(rh.integrity, received_integrity, 4);
    relay_header_pack(cell->payload, &rh);
    crypto_digest_free(backup_digest);
    return 0;
  }
  crypto_digest_free(backup_digest);
  return 1;
}

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.