Check your EC2 security groups for inbound rules that allow unrestricted access (i.e. 0.0.0.0/0 or ::/0) to TCP and UDP port 53 and restrict access to only those IP addresses that require it in order to implement the principle of least privilege and reduce the possibility of a breach. TCP/UDP port 53 is used by the Domain Name Service during DNS resolution (DNS lookup), when the requests are sent from DNS clients to DNS servers or between DNS servers: https://goo.gl/jMfAl.
Allowing unrestricted DNS access can increase opportunities for malicious activity such as such as Denial of Service (DoS) attacks or Distributed Denial of Service (DDoS) attacks.
To determine if your EC2 security groups allow unrestricted DNS access, perform the following:
To update your security groups inbound/ingress configuration in order to restrict DNS access to specific entities (IP addresses, IP ranges, etc), perform the following: