Advice Request Port forwarding and VPN security

[blacksheep]

From time to time I see what some VPN's don't allow any port forwarding. Usually the answer is "For security reasons port forwarding is disabled".
Can someone explain what could be the risks for a VPN provider to enable port forwarding? Why they disable it?

 

[Arequire]

If a VPN client doesn't have a NAT firewall built-in then there's no need for them to offer port forwarding as inbound connections won't be blocked.
As for VPN providers that do offer port forwarding, there's one vulnerability that I'm aware of that can affect them:

IP leak affecting VPN providers with port forwarding | Perfect Privacy

We have discovered a vulnerability that allows an attacker to expose the real IP address of a victim. Perfect Privacy users are protected!

www.perfect-privacy.com

While the vulnerability is easy for VPN providers to mitigate, there's no way to verify whether they've done so or not.

 

[Dave Woski]

From time to time I see what some VPN's don't allow any port forwarding. Usually the answer is "For security reasons port forwarding is disabled".
Can someone explain what could be the risks for a VPN provider to enable port forwarding? Why they disable it?

From what I have read (partially correct) that not all ports are secure so most of the VPNs have blocked the ports. Might be the reason.