Internet-Security.com TCP port 843 details

TCP port 843 was used by Adobe Flash Player for the Flash Socket Policy protocol: clients connecting to arbitrary TCP services first requested crossdomain.xml from a policy server on 843.
Real software that served this file includes Adobe Flash Media Server/Adobe Media Server, Red5 Media Server, SmartFoxServer, and ElectroServer (each shipped or documented a policy daemon on 843).
Many Flash-based multiplayer games and chat/streaming apps deployed a “flashpolicyd” service (e.g., Adobe’s sample socket policy server, Twisted/Python flashpolicy servers, and similar C/Perl daemons) bound to 843.
Web infrastructures sometimes integrated policy serving via modules or small sidecar daemons alongside Nginx/Apache specifically for Flash socket clients.
Legacy deployments may still expose 843 even though Flash reached end-of-life in 2021.
Security note: attackers historically abused overly permissive crossdomain.xml on port 843 to bypass Flash’s same-origin policy, enabling data exfiltration or unauthorized socket access.

TCP 843