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Date: Fri, 6 Dec 2019 16:14:42 +0300
From: ValdikSS <>
Cc: "William J. Tolley" <>,
 Noel Kuntze <>
Subject: Re: [CVE-2019-14899] Inferring and hijacking VPN-tunneled TCP

Please also note that my kind of attack could be performed over the Internet, without direct
connectivity between the attacker and victim, Wi-Fi network or anything.

It has been tested in a real-world Internet environment in 2015, and it worked flawlessly.

On 06.12.2019 16:07, ValdikSS wrote:
> Please also check my article on this topic from 2015
> I used the same technique but with UDP, and it works (at least worked) with Linux, OS X, Windows and Android.
> I used it with old p2p Skype, which allowed to get users' IP address using special "resolver" software or services,
> by user nick name. After getting IP address, you could send UDP packet to the user from your IP address (without
> spoofing) and receive the reply from Skype user, but with VPN source IP address, which allowed to detect
> whether the exact Skype user is connected to the VPN, and to which one, given that his connection is direct (without NAT).
> This also (still) applies to Bittorrent uTP protocol.
> On 05.12.2019 05:38, unknown wrote:
>> Posted by William J. Tolley on Dec 04
>> Hi all,
>> I am reporting a vulnerability that exists on most Linux distros, and
>> other *nix operating systems which allows a network adjacent attacker
>> to determine if another user is connected to a VPN, the virtual IP
>> address they have been assigned by the VPN server, and whether or not
>> there is an active connection to a given website. Additionally, we are
>> able to determine the exact seq and ack numbers by counting encrypted
>> packets and/or...

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