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Attackers can decloak routing-based VPNs

We discovered a fundamental design problem in VPNs and we're calling it TunnelVision. This problem lets someone see what you're doing online, even if you think you're safely using a VPN.

To help make this work accessible to as many people as possible, we are structuring this blog post to walk through the fundamentals of networking, VPN technology, and DHCP to fully explain the decloaking behavior. For example, a user can trust that the layers lower than their browser (HTTP) are determining how to send electricity over a cable (Coax), knows who to talk to (Ethernet, IP), and ensure correct data delivery to the recipient server (TCP). The main concept to understand is that DHCP provides a time-based lease for IP addresses, and it contains many additional features called options that allow you to adjust the configuration of devices remotely and dynamically.

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