A port is a number used to identify specific communication types. When a port is open it means that a program or service is listening for data coming through that port.
If you perform a scan of your Instapage landing pages and find some open ports, the most common explanations are:
- Port 443 is necessary to securely serve a landing page using HTTPS/SSL - encrypted transfers.
- Port 80 is necessary to securely serve a landing page using HTTP - unencrypted transfers.
- Certain ports remain open so that the Google Load Balancer can work properly. More information can be found here: https://cloud.google.com/load-balancing/docs/tcp#open_ports.
This is not a vulnerability and should be considered a false positive. We do not have control over such ports, but there are no servers behind them with exposed ports such as RDP (Remote Desktop Protocol).
Our clients can test and confirm this themselves by attempting an RDP connection on such ports. Some examples in this scenario include (but may not be limited to) the following port numbers: 389, 3389, 5222, 5900, 9092.