Google Chrome will block the browser’s access to TCP port 554 to protect against attacks using the NAT Slipstreaming 2.0 vulnerability. The vulnerability allows malicious scripts to bypass a website visitor’s NAT firewall and access any TCP/UDP port on the visitor’s internal network. Google and Safari developers are also discussing blocking access to port 10080, which Firefox already blocks, but are hesitant due to legitimate web browser requests to that port. When a user attempts to connect to a website on these ports, users are shown an error message stating ‘ERR_UNSAFE_PORT’
Source: https://www.bleepingcomputer.com/news/security/google-chrome-to-block-port-554-to-stop-nat-slipstreaming-attacks/