Apex domains cannot have CNAME records.
Question and response
Question
dig kubra.com. NS
Answer
kubra.com. 5 NS pdns112.ultradns.biz.
kubra.com. 5 NS pdns112.ultradns.com.
kubra.com. 5 NS pdns112.ultradns.net.
kubra.com. 5 NS pdns112.ultradns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0