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Re: [Ntp] Details of the fragmentation attacks against NTP and port randomization

Hal Murray <hmurray@megapathdsl.net> Wed, 05 June 2019 21:57 UTC

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To: Danny Mayer <mayer@pdmconsulting.net>
cc: NTP WG <ntp@ietf.org>, hmurray@megapathdsl.net
From: Hal Murray <hmurray@megapathdsl.net>
In-Reply-To: Message from Danny Mayer <mayer@pdmconsulting.net> of "Wed, 05 Jun 2019 14:35:42 EDT." <8e3f7027-ea04-3e33-274f-0c65f499af7d@pdmconsulting.net>
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Date: Wed, 05 Jun 2019 14:57:10 -0700
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Subject: Re: [Ntp] Details of the fragmentation attacks against NTP and port randomization
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mayer@pdmconsulting.net said:
> The opposition is due to the fact that randomizing the ports doesn't solve
> the underlying security issue. If I'm an attacker off-path and can get to the
> target system, I can just run nmap and find out all of the open ports leaving
> just a few ports to check. Randomizing ports by itself solves nothing here. 

There is an important idea that isn't specified in "randomization".  When does 
the randomization happen?

Case A: When a client decides to use IP Address a.b.c.d as a server, open a 
socket.

Case B: When a client decides to send a packet to IP Address a.b.c.d, open a 
socket.  When the response arrives (or timeout) close the socket.

nmap will find Case A type systems.  It has a small chance of finding systems 
using Case B.


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