MITM Problem in Site2Site Configuration

[Woodsomeister]

Hello,

i have a Peer to Peer (SSL/TLS) OpenVPN connection.

In the logs of both of my two clients the following line appears:
"WARNING: No server certificate verification method has been enabled. ..."

The same CA is stored on both the client and server side and is also selected in the VPN settings. Valid certificates are also issued via this CA.

So far everything works fine, but do I have to worry about security issues because of a possible MITM attack? Can an attacker give the clients a fake OpenVPN server?

All peer to peer clients and also the server run with pfSense version 2.4.4p3.

Thanks

[Woodsomeister]

I got rid of this error by adding "remote-cert-tls server" in the additional configuration options field. But I did not understand why this is necessary.