Apex domains cannot have CNAME records.
Question and response
Question
dig viabrs.com.br. NS
Answer
viabrs.com.br. 2 NS ns1.viabrs.com.br.
viabrs.com.br. 2 NS ns2.viabrs.com.br.
Authority
The response has no authority records.
Additional
ns1.viabrs.com.br. 2 A 177.53.141.4
ns2.viabrs.com.br. 2 A 177.53.140.4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0