Abnormal DNS resolution behavior is detected on an internal network.

This is a textbook case of Intranet DNS Poisoning, often combined with ARP spoofing, as described in CEH v13 Network Sniffing and MITM Attacks. The attacker positions themselves inside the local network, intercepts DNS requests, and responds faster than the legitimate DNS server.

ARP spoofing enables the attacker to perform a Man-in-the-Middle attack, allowing sniffing and modification of DNS traffic. CEH v13 notes that faster rogue responses are a strong indicator of local DNS poisoning.