In ectd before versions 3.4.10 and 3.3.23, gateway TLS authentication is only applied to endpoints detected in DNS SRV records. When starting a gateway, TLS authentication will only be attempted on endpoints identified in DNS SRV records for a given domain, which occurs in the discoverEndpoints function. No authentication is performed against endpoints provided in the --endpoints flag. This has been fixed in versions 3.4.10 and 3.3.23 with improved documentation and deprecation of the functionality.
https://github.com/etcd-io/etcd/security/advisories/GHSA-wr2v-9rpq-c35q
https://github.com/etcd-io/etcd/blob/master/Documentation/op-guide/gateway.md