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Re: Security considerations for DNS rebinding

From: Maciej Stachowiak <mjs@apple.com>
Date: Tue, 09 Feb 2010 10:40:27 -0800
Cc: Tim <tim-projects@sentinelchicken.org>, HTTP Working Group <ietf-http-wg@w3.org>
Message-id: <E9FFBB2A-64FB-4EDE-9062-C476AB65DC27@apple.com>
To: Adam Barth <w3c@adambarth.com>

On Feb 9, 2010, at 10:08 AM, Adam Barth wrote:

> On Tue, Feb 9, 2010 at 6:23 AM, Tim <tim-projects@sentinelchicken.org> wrote:
>>> The DNS Spoofing security considerations subsection has a
>>> requirement that actually increases the risk of DNS rebinding attacks.
>>> It says that "If HTTP clients cache the results of host name lookups
>>> in order to achieve a performance improvement, they must observe the
>>> TTL information reported by DNS". Clients that follow this advice will
>>> be at greater risk than if they give cached DNS lookup results a floor
>>> on time-to-live, or keep a DNS resolution result "pinned" so long as
>>> any resource from that domain is active. Those are the simplest
>>> client-side mitigation strategies for DNS rebinding attacks. If DNS
>>> lookups are cached in the browser for a minimum of, say, an hour,
>>> there is much less risk of a DNS rebinding attack, because the
>>> attacker must get the user to keep a page open for at least an hour to
>>> be able to perform the rebinding attack.
>> 
>> While I'm not an expert on DNS rebinding, I'm afraid I don't agree
>> that DNS pinning helps prevent rebinding attacks.
> 
> DNS pinning is not a great solution to DNS rebinding, and I would
> hesitate to recommend it to user agent implementors.  For details,
> please see:
> 
> http://www.adambarth.com/papers/2007/jackson-barth-bortz-shao-boneh.pdf

I don't necessarily think HTTPbis should recommend it. However, I don't think HTTPbis should make it a MUST-level requirement not to do any DNS pinning, nor claim that following that requirement is necessary for security.

> 
> On the other hand, Host header checking is effective, and it seems
> valuable for HTTPbis to recommend it to server implementors.

I think that is the important recommendation to add.

Regards,
Maciej
Received on Tuesday, 9 February 2010 18:41:00 GMT

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