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

Danny Mayer <mayer@ntp.org> Mon, 10 June 2019 23:25 UTC

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To: Fernando Gont <fgont@si6networks.com>, Ask Bjørn Hansen <ask@develooper.com>
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> <f3b359e6-5e22-ba6d-385a-23d3a62f0330@si6networks.com>
From: Danny Mayer <mayer@ntp.org>
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Date: Mon, 10 Jun 2019 19:25:44 -0400
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Archived-At: <https://mailarchive.ietf.org/arch/msg/ntp/20MIfQ_KnnjurU9_loqqbHGBvlI>
Subject: Re: [Ntp] Details of the fragmentation attacks against NTP and port randomization
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On 6/7/19 6:56 AM, Fernando Gont wrote:
> 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.
>
Actually he is right. Not all NTP clients are also servers. It has
nothing to do with whether or not to randomize the source port.

Danny