Boxes Unable to Connect Back to my Machine

I am unable to have boxes connect back to my machine in certain circumstances, which makes some boxes impossible to complete. For the example here, I am attempting the Responder box under tier 1 of starting point and I am running Parrot OS on bare metal. I am able to run/connect my starting point vpn and gain access to the box’s IP. I am able to ping the box and get a response, I am able run a successful nmap scan, I can curl the box’s html, etc. Later on, I am supposed to set up responder to listen on tun0 and then alter the url to connect back to my machine via my tun0 address with RFI (task 6/page 8 in the walkthrough). Eventually the page times out and I receive the same error as shown in the walkthrough, but my responder never hears anything. Any thoughts on what might be happening? I can’t seem to find anyone else who has had this particular problem…

This also occurs on all other boxes where I have to RCE curl/wget back to an http server set up on my machine or if I am trying to use netcat instead of responder in similar situations. Basically my machine and the box are able to communicate unless I am attempting to reach my machine from the box.

Most likely your problem is virtualization networking issue or host firewall. You could spin up another OS and perhaps run nmap against your academy box within your LAN. If you see any ports closed/filtered, your host firewall is active. I usually add adaptors to my host and use a bridged adapter with Virtual Box to “simplify” the networking. Using the internal NAT can be a problem at times and you might have to remove and re-add virtual network components.