static int cac_get_serial_nr_from_CUID(sc_card_t* card, sc_serial_number_t* serial)
{
	cac_private_data_t * priv = CAC_DATA(card);

	SC_FUNC_CALLED(card->ctx, SC_LOG_DEBUG_NORMAL);
        if (card->serialnr.len)   {
                *serial = card->serialnr;
                SC_FUNC_RETURN(card->ctx, SC_LOG_DEBUG_NORMAL, SC_SUCCESS);
         }
 	if (priv->cac_id_len) {
 		serial->len = MIN(priv->cac_id_len, SC_MAX_SERIALNR);
		memcpy(serial->value, priv->cac_id, priv->cac_id_len);
 		SC_FUNC_RETURN(card->ctx, SC_LOG_DEBUG_NORMAL, SC_SUCCESS);
 	}
 	SC_FUNC_RETURN(card->ctx, SC_LOG_DEBUG_NORMAL, SC_ERROR_FILE_NOT_FOUND);
}

The product calls free() twice on the same memory address, potentially leading to modification of unexpected memory locations.