Internet-Security.com TCP port 3128 details

TCP 3128 is the default port for the Squid caching HTTP proxy (IANA service name: squid-http).
Standard Squid packages on Debian/Ubuntu/CentOS commonly listen on 3128 for explicit proxying (HTTP and HTTPS via CONNECT).
pfSense’s Squid package and OPNsense’s Web Proxy (Squid) typically use 3128 for client proxy connections.
ClearOS Web Proxy (Squid-based) and Artica Proxy also default to 3128 in many deployments.
Content filters often chain to a local Squid on 3128 (e.g., DansGuardian in front of Squid).
Security note: 3128 is frequently scanned and abused when left as an open proxy; attackers leverage misconfigured Squid services on this port to relay traffic, spam, scraping, and other anonymized activity.

TCP 3128