NSA: DNS over HTTPS Provides “False Sense of Security”

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The US National Security Agency (NSA) has warned enterprises that adoption of encrypted DNS services can lead to a false sense of security and even disrupt their own DNS-monitoring tools.

DNS over HTTPS (DoH) has become an increasingly popular way to improve privacy and integrity by protecting DNS traffic between a client and a DNS resolver from unauthorized access. This can help to prevent eavesdropping and manipulation of DNS traffic.

However, although such services are useful for home and mobile users and networks not using DNS controls, they are not recommended for most enterprises, the US security agency claimed in a new report.

DoH is “not a panacea,” as it doesn’t guarantee that threat actors can’t see where a client is going on the web, said the NSA.

“DoH is specifically designed to encrypt only the DNS transaction between the client and resolver, not any other traffic that happens after the query is satisfied,” the report noted.

“While this allows clients to privately obtain an IP address based on a domain name, there are other ways cyber-threat actors can determine information without reading the DNS request directly, such as monitoring the connection a client makes after the DNS request.”

Moreover, DoH can actually impair network monitoring tools designed to spot suspicious activity in DNS traffic.

“DoH encrypts the DNS traffic, which prevents enterprises from monitoring DNS with these network-based tools unless they are breaking and inspecting TLS traffic. If DoH is used with the enterprise resolver, then inspection can still occur at the resolver or using resolver logs,” the report continued.

“However, if external DoH resolvers are not blocked and DoH is enabled on the user’s browser or OS to use a different resolver, there could be issues gaining visibility into that encrypted DNS traffic.”

Malware can also use DoH to hide its C&C communications traffic, the NSA warned.

The agency urged enterprises that use monitoring tools to avoid using DoH inside their networks.

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