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

Watson Ladd <watsonbladd@gmail.com> Tue, 04 June 2019 03:16 UTC

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From: Watson Ladd <watsonbladd@gmail.com>
Date: Mon, 03 Jun 2019 20:16:35 -0700
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To: Danny Mayer <mayer@pdmconsulting.net>
Cc: Watson Ladd <watson=40cloudflare.com@dmarc.ietf.org>, NTP WG <ntp@ietf.org>
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Subject: Re: [Ntp] Details of the fragmentation attacks against NTP and port randomization
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On Mon, Jun 3, 2019 at 8:10 PM Danny Mayer <mayer@pdmconsulting.net> wrote:
>
> On 6/3/19 2:24 PM, Watson Ladd wrote:
>
> > Dear all,
> >
> > The debate over client port randomization is missing an important
> > fact: off-path attacks against NTP are not prevented by the origin
> > timestamp due to the OS handling of fragmentation. In
> > http://www.cs.bu.edu/~goldbe/papers/NTPattack.pdf we see that sending
> > a properly crafted IP fragment can selectively overwrite NTP packets,
> > thus allowing an attacker to modify received data without overwriting
> > the origin timestamp. I would recommend we adopt port randomization
> > to handle this problem.
> >
> > Sincerely,
> > Watson Ladd
>
> Actually if you read Section VI you will see that the last sentence of
> that section states that they do not consider it to be a sufficient defense.

I concur. Sadly we don't have anything better until we see NTS deployment.
>
> Danny
>
>
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