There is a significant problem when security related RRs with the same owner name as a CNAME RR are retrieved from a non-security-aware server. In particular, an initial retrieval for the CNAME or any other type will not retrieve any associated signature, key, or NXT RR. For types other than CNAME, it will retrieve that type at the target name of the CNAME (or chain of CNAMEs) and will return the CNAME as additional information. In particular, a specific retrieval for type SIG will not get the SIG, if any, at the original CNAME domain name but rather a SIG at the target name.
In general, security aware servers MUST be used to securely CNAME in DNS. Security aware servers must (1) allow KEY, SIG, and NXT RRs along with CNAME RRs, (2) suppress CNAME processing on retrieval of these types as well as on retrieval of the type CNAME, and (3) automatically return SIG RRs authenticating the CNAME or CNAMEs encountered in resolving a query. This is a change from the previous DNS standard which prohibited any other RR type at a node where a CNAME RR was present.