DNS tunneling is a technique that encodes data of other programs and protocols in DNS queries, including data payloads that can be used to control a remote server and applications1. DNS exfiltration is a form of DNS tunneling that allows attackers to extract data from a compromised system by sending encoded DNS requests to a domain under their control2. The direction of the data transfer in DNS exfiltration is outbound, meaning from the victim's network to the attacker's network. This is different from inbound, which means from the attacker's network to the victim's network, or north-south and east-west, which are terms used to describe the traffic flow between different network segments or zones3. Outbound DNS requests are often allowed by default in many firewalls and network devices, making them an attractive channel for data exfiltration4. However, DNS exfiltration can be detected and prevented by using security solutions that monitor and analyze DNS traffic for anomalies and malicious patterns5.
References: 1: Improvements to DNS Tunneling & Exfiltration Detection - Cisco Umbrella 2: DNS Exfiltration & Tunneling: How it Works & DNSteal Demo Setup 3: What Is DNS Tunneling? - Palo Alto Networks 4: DNS Data Exfiltration and DNS Tunneling | Vercara 5: DNS Exfiltration: The Light at the End of the DNS Tunnel - site