Internet-Security.com UDP port 518 details

UDP port 518 is used by the ntalk (New Talk) service, a classic real-time text chat protocol on Unix-like systems.
Server daemons such as ntalkd/in.ntalkd on BSD variants (FreeBSD, OpenBSD, NetBSD) and older Solaris listen on UDP 518.
Linux distributions have provided the service via talkd implementations (e.g., inetutils-talkd or netkit-based ntalkd), interoperating with clients like talk and ytalk.
Historically, multiple talk/ntalk daemons have had remote vulnerabilities and the protocol lacks authentication, so it’s often disabled today for security reasons.

UDP 518