👨‍💻 Chris Hiszpanski


When a TCP/IP client connects to a new remote host and port, it must select a local port to use for the connection. Usually, any free port will do, so most applications leave local port selection to the kernel. The kernel selects a port at random from the ephemeral port range. Except the selection isn’t really random. As it turns out, the selected port can be predicted in advance, revealing kernel state information.