Apex domains cannot have CNAME records.
Question and response
Question
dig CDN.GBlNeT.ru. NS
Answer
CDN.GBlNeT.ru. 5 NS ns1.CDN.GBlNeT.ru.
CDN.GBlNeT.ru. 5 NS ns.GBlNeT.ru.
Authority
The response has no authority records.
Additional
ns.gblnet.RU. 1 A 95.140.80.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0