VPNs are vulnerable to what is called a “port fail” according to Perfect Privacy, which can expose users’ IP addresses.
The VPN provider published a blog post last week, which detailed the vulnerability in VPNs that use port forwarding and are based on protocols like OpenVPN, IPSec, or PPTP.
It’s important to point out that in order for an attacker to carry out an attack, they need to be using the same VPN service as their victim. Then the attacker must lure the victim into clicking a link that they control the port of, in order to gain access to the IP address.
“If the attacker has port forwarding activated for his account on the same server, he can find out the real IP addresses of any user on the same VPN server by tricking him into visiting a link that redirects the traffic to a port under his control,” says Perfect Privacy.
In particular, BitTorrent users are some of the most vulnerable, according to another security researcher.
Perfect Privacy says it tested nine different VPNs to come to its conclusions, and makes a couple of suggestions to its competitors:
Affected VPN providers should implement one of the following:
Have multiple IP addresses, allow incoming connections to ip1, exit connections through ip2-ipx, have portforwardings on ip2-ipx
On Client connect set server side firewall rule to block access from Client real ip to portforwardings that are not his own.
The Register reports that Private Internet Access, one of the bigger VPNs on the market, has patched the hole and even paid $5,000 to Perfect Privacy for its efforts.
Perfect Privacy has not specified what other VPNs are affected.