Internet-Security.com UDP port 27018 details

Valve Steam/Source-engine traffic uses UDP ports 27000–27100, so UDP 27018 is legitimately used by Steam clients and servers.
Source Dedicated Server (SRCDS) games—such as Counter-Strike 2/CS:GO, Team Fortress 2, Garry’s Mod, and many other Steam-based titles—often bind/query on UDP 27018 when multiple servers run on the same host (ports typically increment from 27015 upward).
Rust and other Steamworks-powered games may also use UDP 27018 for server query/game traffic within this range.
Steamworks/Steam Datagram Relay (SDR) and matchmaking can traverse UDP 27018 as part of the 27000–27100 range.
These UDP game ports are frequent targets for DDoS attacks against public game servers.

UDP 27018