Critical 'Port-Fail' Vulnerability Reveals Real-IP Addresses of VPN Users

A newly discovered flaw affecting all VPN protocols and operating systems has the capability to reveal the real IP-addresses of users' computers, including BitTorrent users, with relative ease.
Actually, The vulnerability dubbed Port Fail by VPN provider Perfect Privacy (PP) who discovered the issue, is a simple port forwarding trick and affects those services that:

• Allow port forwarding
• Have no protection against this specific attack

Port Forwarding trick means if an attacker uses the same VPN (Virtual Private Network) as the victim, then the real IP-address of the victim can be exposed by forwarding Internet traffic to a specific port.
"The crucial issue here is that a VPN user connecting to his own VPN server will use his default route with his real IP address, as this is required for the VPN connection to work," Perfect Privacy wrote in a blog post on Thursday.
Also Read: This Secure Operating System Can Protect You Even if You Get Hacked.
Port Fail affects all VPN protocols including…
OpenVPN
IPSec
…as well as applies to all operating systems, posing a huge privacy risk.

Details about the leak

The attacker needs to meet the following requirements:

• Has an active account at the same VPN provider as the victim
• Knows victim’s VPN exit IP address (can be obtained by various means, e.g. IRC or torrent client or by making the victim visit a website under the attackers control)
• The attacker sets up port forwarding. It makes no difference whether the victim has port forwarding activated or not.

The IP leak can then be triggered as follows:

1. Victim is connected to VPN server 1.2.3.4
2. Victim’s routing table will look something like this:
3. 0.0.0.0/0 -> 10.0.0.1 (internal vpn gateway ip)
4. 1.2.3.4/32 -> 192.168.0.1 (old default gateway)
5. Attacker connects to same server 1.2.3.4 (knows victim’s exit through IRC or other means)
6. Attacker activates Port Forwarding on server 1.2.3.4, example port 12345
7. Attacker gets the victim to visit 1.2.3.4:12345 (for example via embedding <img src=”http://1.2.3.4:12345/x.jpg”> on a website)
8. This connection will reveal the victim’s real IP to the attacker because of the “1.2.3.4/32 -> 192.168.0.1” vpn route.

How Does 'Port Fail' Work?

A successful IP address leak attack requires an attacker to be on the same VPN network as the victim and to know the victim's VPN exit IP address, which could be discovered by tricking a victim into visiting a website control controlled by the attacker.
For example, an attacker with port forwarding enabled can see the request from the victim's actual IP addresses by tricking the victim into opening an image file.
The same attack is possible for BitTorrent users, but, in this case, there is no need for the attacker to redirect the victim to their page.
In this case, the attacker only with the activated port forwarding for the default BitTorrent port, can expose the real IP-address of a VPN user on the same network.
Also Read: Hackers Backdooring Cisco WebVPN To Steal Customers' Passwords

Affected VPN Providers

The flaw affected various large VPN providers. Perfect Privacy tested nine VPN providers out of which five were found to be vulnerable to this flaw and were alerted last week.
VPN providers including Private Internet Access (PIA), Ovpn.to and nVPN have fixed the issue before publication.
However, the company warned, "other VPN providers may be vulnerable to this attack as we could not possibly test all."
VPN aims to make you sure that your real identity remains anonymous on the Internet so that nobody could track the origin of your connection back to you, but this newly discovered flaw shows that it's quite easy to bypass this on some VPN providers.