Google Chrome to block port 554 to stop NAT Slipstreaming attacks By 01:21 PM Google Chrome will block the browser's access to TCP port 554 to protect against attacks using the NAT Slipstreaming 2.0 vulnerability. Last year, security researchers disclosed a new version of the NAT Slipstreaming vulnerability that allows malicious scripts to bypass a website visitor's NAT firewall and access any TCP/UDP port on the visitor's internal network. Illustration of the NAT Slipstreaming 2.0 attack As this vulnerability only works on specific ports monitored by a router's Application Level Gateway (ALG), browser developers, including Google, Safari, and Mozilla, have been blocking vulnerable ports that do not receive a lot of traffic.