Unreachable Server Behind Firewall (Simulation of Reverse Shell)
A solution to this problem is to have the server(victim) reach out and connect to the client. In such a case, the client(attacker) will listen on a port, say, port 80, and the server will then attempt to connect every 5 seconds. If the client is not up, the server waits 5 seconds and then tries again. If a client is up, it will then establish a connection and gives a shell to the client. The client will then be able to send commands, and they will execute on the server side. This technology is called Reverse Connection Shell.
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Download ReverseShell Tools by Cagdas Ulucan