Design Flaw in AS3 Socket Handling Allows Port Probing = Flash Port Scanner

Summary

Due to a design flaw in ActionScript 3 socket handling, compiled Flash movies are able to scan for open TCP ports on any host reachable from the host running the SWF, bypassing the Flash Player Security Sandbox Model and without the need to rebind DNS.

Technical background

In AS3 Adobe introduced a new socket-related event called SecurityErrorEvent. This event is always thrown when a Flash Player tries to connect to a socket that it is not allowed to connect to.

The Problem with the SecurityErrorEvent is that it's thrown immediately when a Flash Player tries to connect to a closed TCP port. If a service is listening on that port the Flash Player writes the string "" and waits for response from the service. Nearly no TCP-service will respond to this request.

We can assume the following: When trying to connect to a socket that the SWF is not allowed to and it doesn't get a SecurityErrorEvent within 2 seconds the port is most likely open.

A new Flash player instance is used for every probed port because the Flash Player sends only one policy-file request per player per host per port.

http://scan.flashsec.org/