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

Fernando Gont <fgont@si6networks.com> Fri, 07 June 2019 11:05 UTC

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To: Ask Bjørn Hansen <ask@develooper.com>, Danny Mayer <mayer@pdmconsulting.net>
Cc: ntp@ietf.org
References: <CAN2QdAGS20q=7+r+qMFEBBu4gNmSDR9-vYDbvgC=ZnqWLEU-6w@mail.gmail.com> <739c2eaa-05f1-0b30-4b64-fc5d3f91ce5b@pdmconsulting.net> <a3a545cf-d83d-a2c7-ad6c-3e349de78615@si6networks.com> <9f75e400-cf2f-053f-ed06-f4d6df415eaf@pdmconsulting.net> <E3F91EE1-4EE8-4D3C-95E9-135D1CB1DF8A@develooper.com>
From: Fernando Gont <fgont@si6networks.com>
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Date: Fri, 07 Jun 2019 13:56:34 +0300
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Subject: Re: [Ntp] Details of the fragmentation attacks against NTP and port randomization
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On 5/6/19 05:45, Ask Bjørn Hansen wrote:
> 
> 
>> On Jun 5, 2019, at 10:41 AM, Danny Mayer <mayer@pdmconsulting.net
>> <mailto:mayer@pdmconsulting.net>> wrote:
>>
>> Furthermore the attacker doesn't know the server being used by the NTP
>> client so the IP address of that server will be invalid as well. 
> 
> This doesn’t seem right. There are much much less NTP servers in the
> world than there are clients. Even an attacker wildly guessing will have
> a limited scope of guessing (versus “every possible IP”).

Indeed, this is plain wrong. e.g. see the analysis in RFC5927 and RFC4953.

Not only we seem to be ignoring the advice in this area (RFC6056), but
we also seem to be ignoring 5+ years of work on the transport area on
these topics.

Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: fgont@si6networks.com
PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492

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