Internet-Security.com UDP port 443 details

IETF QUIC uses UDP/443 and underpins HTTP/3; modern browsers (Chrome, Firefox, Edge, Safari) use it to reach major sites and CDNs like Google/YouTube, Facebook, Cloudflare, Akamai, Fastly, and Wikipedia.
Web servers and proxies that speak HTTP/3 on UDP/443 include Caddy, NGINX 1.25+ with QUIC, LiteSpeed, and Envoy.
Windows SMB over QUIC (Windows 11 and Windows Server 2022) uses UDP/443 by default for secure file sharing.
Cisco AnyConnect SSL VPN and Fortinet SSL VPN use DTLS over UDP/443 for their VPN data channels.
Apple iCloud Private Relay uses QUIC over UDP/443 between devices and relay partners such as Cloudflare and Akamai.
DNS-over-HTTPS services that support HTTP/3 (e.g., Cloudflare 1.1.1.1 and Google Public DNS DoH) use UDP/443 because HTTP/3 runs on QUIC.
Security note: providers like Cloudflare report QUIC/UDP/443 being targeted in large DDoS attacks, and some adversaries use QUIC over 443 to blend command-and-control with normal HTTP/3 traffic.

UDP 443