Dubbed NAT Slipstreaming, the attack can be triggered when the victim visits a specially crafted website, exploiting the browser and Application Level Gateway (ALG), a connection tracking mechanism present in firewalls, NATs, and routers.

According to the researcher, the attack chains “internal IP extraction via timing attack or WebRTC, automated remote MTU and IP fragmentation discovery, TCP packet size massaging, TURN authentication misuse, precise packet boundary control, and protocol confusion through browser abuse.”

Leveraging the fact that the destination port is opened by the NAT or firewall, the attack can bypass existing browser-based port restrictions.