Internet-Security.com UDP port 53 details

UDP port 53 is used by the Domain Name System (DNS) for query/response traffic in real deployments.
Server software that listens on UDP 53 includes BIND (named), Microsoft DNS Server (Windows Server), Unbound, PowerDNS (Authoritative and Recursor), Knot DNS, NSD, CoreDNS (e.g., in Kubernetes), and dnsmasq (common on home routers/OpenWrt).
Public resolvers answering on UDP 53 include Google Public DNS (8.8.8.8/8.8.4.4), Cloudflare (1.1.1.1), and Quad9 (9.9.9.9).
Enterprise DNS appliances using UDP 53 include Infoblox NIOS and BlueCat DNS/DHCP servers.
Client-side stub resolvers that send DNS over UDP 53 include the Windows DNS Client service, systemd-resolved on Linux, and the glibc resolver; many consumer routers forward DNS over UDP 53.
Active Directory environments use DNS Dynamic Updates (RFC 2136) over UDP 53 to update Microsoft DNS, and EDNS0 extends UDP 53 DNS with larger payloads in production.
Abuse: attackers leverage open resolvers on UDP 53 for reflection/amplification DDoS, use DNS tunneling tools (e.g., iodine, DNScat2) for data exfiltration/C2, and target UDP 53 resolvers with cache-poisoning attacks (e.g., Kaminsky-style).

UDP 53