Application Layer Protocol: DNS
Adversaries may communicate using the Domain Name System (DNS) application layer protocol to avoid detection/network filtering by blending in with existing traffic. Commands to the remote system, and often the results of those commands, will be embedded within the protocol traffic between the client and server.
The DNS protocol serves an administrative function in computer networking and thus may be very common in environments. DNS traffic may also be allowed even before network authentication is completed. DNS packets contain many fields and headers in which data can be concealed. Often known as DNS tunneling, adversaries may abuse DNS to communicate with systems under their control within a victim network while also mimicking normal, expected traffic.
|Filter Network Traffic||
Consider filtering DNS requests to unknown, untrusted, or known bad domains and resources. Resolving DNS requests with on-premise/proxy servers may also disrupt adversary attempts to conceal data within DNS packets.
|Network Intrusion Prevention||
Network intrusion detection and prevention systems that use network signatures to identify traffic for specific adversary malware can be used to mitigate activity at the network level.
Analyze network data for uncommon data flows (e.g., a client sending significantly more data than it receives from a server). Processes utilizing the network that do not normally have network communication or have never been seen before are suspicious. Analyze packet contents to detect application layer protocols that do not follow the expected protocol standards regarding syntax, structure, or any other variable adversaries could leverage to conceal data.
Monitor for DNS traffic to/from known-bad or suspicious domains.
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