I'm trying to scan my targets for open ports. However, NMAP reports all of them as 'open'. I know there's a firewall in between.
I tried the SYN scan, and when I check the traffic in WireShark I see the SYN/ACK reply for every port. Same goes for the TCP Connect scan, I see the full handshake, etc..
If I for example try to connect to 5900 using vnc viewer, I receive the connecting message but that's it.
I'm looking for a reliable way to check for open ports.