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

Fernando Gont <fgont@si6networks.com> Tue, 04 June 2019 07:29 UTC

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To: Danny Mayer <mayer@pdmconsulting.net>, Watson Ladd <watson=40cloudflare.com@dmarc.ietf.org>, NTP WG <ntp@ietf.org>
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From: Fernando Gont <fgont@si6networks.com>
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Message-ID: <a3a545cf-d83d-a2c7-ad6c-3e349de78615@si6networks.com>
Date: Tue, 04 Jun 2019 09:39:03 +0300
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Archived-At: <https://mailarchive.ietf.org/arch/msg/ntp/VZYOFbeBAB_hSo4izDIvF9i8xlg>
Subject: Re: [Ntp] Details of the fragmentation attacks against NTP and port randomization
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On 4/6/19 06:09, Danny Mayer 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.

Wasn't Your argument that the timestamp was enough to mitigate off-path
attacks?


-- 
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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