The National Security Agency (NSA) has released an information sheet with guidance on adopting encrypted Domain Name System (DNS) over Hypertext Transfer Protocol over Transport Layer Security (HTTPS), referred to as DNS over HTTPS (DoH). When configured appropriately, strong enterprise DNS controls can help prevent many initial access, command and control, and exfiltration techniques used by threat actors.

Use of the Internet relies on translating domain names (like “nsa.gov”) to Internet Protocol addresses. This is the job of the Domain Name System (DNS). In the past, DNS lookups were generally unencrypted, since they have to be handled by the network to direct traffic to the right locations. DNS over Hypertext Transfer Protocol over Transport Layer Security (HTTPS), often referred to as DNS over HTTPS (DoH), encrypts DNS requests by using HTTPS to provide privacy, integrity, and “last mile” source authentication with a client’s DNS resolver. It is useful to prevent eavesdropping and manipulation of DNS traffic. While DoH can help protect the privacy of DNS requests and the integrity of responses, enterprises that use DoH will lose some of the control needed to govern DNS usage within their networks unless they allow only their chosen DoH resolver to be used. Enterprise DNS controls can prevent numerous threat techniques used by cyber threat actors for initial access, command and control, and exfiltration. Using DoH with external resolvers can be good for home or mobile users and networks that do not use DNS security controls. For enterprise networks, however, NSA recommends using only designated enterprise DNS resolvers in order to properly leverage essential enterprise cybersecurity defenses, facilitate access to local network resources, and protect internal network information. The enterprise DNS resolver may be either an enterprise-operated DNS server or an externally hosted service. Either way, the enterprise resolver should support encrypted DNS requests, such as DoH, for local privacy and integrity protections, but all other encrypted DNS resolvers should be disabled and blocked. However, if the enterprise DNS resolver does not support DoH, the enterprise DNS resolver should still be used and all encrypted DNS should be disabled and blocked until encrypted DNS capabilities can be fully integrated into the enterprise DNS infrastructure. This guidance explains the purpose behind the DoH design and the importance of configuring enterprise networks appropriately to add benefits to, but not hinder, their DNS security controls. The following recommendations will assist enterprise network owners and administrators to balance DNS privacy and governance.