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Date: Thu, 16 Oct 2014 14:34:25 -0600
From: Kurt Seifried <>
Subject: Re: attacking hsts through ntp

On 16/10/14 01:45 PM, Hanno Böck wrote:
> Am Thu, 16 Oct 2014 09:56:06 -0600
> schrieb Kurt Seifried <>:
>> The obvious solution being to whitelist your site (in the
>> chrome/firefox source code)if you truly care:
> No.
> While this is neat (and I already did this for my most important
> domains) this won't help.
> The reason: HSTS preloaded sites are handled exactly the same way as
> normal HSTS sites - they can expire. Chrome sets a maximum timeout for
> HSTS of 1000 days for preloaded sites. That was elaborated in the talk
> today. He demonstrated the attack on google mail which is in this
> whitelist. Set clock 3 years into the future and youre done.

I did not know that. One concern I have is also HSTS has no tools to
manage them in browsers, at least when I last checked, has that changed?
There is some room for DoS due to this on the client side.

> It could be argued that it is wrong to expire preloaded HSTS sites. But
> the very same attack applies to HPKP which basically has to expire,
> because you don't want to use keys forever.

If people say "I use HSTS, so much so that I want you to whitelist it IN
the source code forever" I'm pretty sure they never want it to expire
(at least that was my thought when I got my domains whitelisted).

Kurt Seifried -- Red Hat -- Product Security -- Cloud
PGP A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993

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