Subject: Roman Danyliw's No Objection on draft-ietf-httpbis-cache-header-09: (with COMMENT)

From: Roman Danyliw via Datatracker <[email-masked]>
Date: Tue, 10 Aug 2021 15:28:58 -0700

Roman Danyliw has entered the following ballot position for
draft-ietf-httpbis-cache-header-09: No Objection

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COMMENT:
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** Is there further guidance that can be provided to inform the tradeoff
between operational and security considerations?

(a) Section 2 says “While these parameters are OPTIONAL, caches are encouraged
to provide as much information as possible.”

(b) Section 6 says “Attackers can use the information in Cache-Status to probe
the
   behaviour of the cache (and other components), and infer the activity
   of those using the cache.  The Cache-Status header field may not
   create these risks on its own, but can assist attackers in exploiting
   them.

   For example, knowing if a cache has stored a response can help an
   attacker execute a timing attack on sensitive data.  Exposing the
   cache key can help an attacker understand modifications to the cache
   key, which may assist cache poisoning attacks.  See [ENTANGLE] for
   details.”

On the one hand, the operational guidance in (a) seems to be saying share as
much as you can to support debugging.  However, the security considerations of
(b) reminds the reader that the presence these parameters can be exploited.  Is
there any additional guidance that can be provided on how this tradeoff could
or should be made?

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From: Mark Nottingham <[email-masked]>
Date: Wed, 11 Aug 2021 12:13:45 +1000

Hi Roman,

> On 11 Aug 2021, at 8:28 am, Roman Danyliw via Datatracker <[email-masked]> wrote:
> 

It's a good question. I'm struggling to come up with anything, I suspect that's because the tradeoff is situational, depending upon the proxy's threat model, etc.

If you (or anyone else) can come up with more specific text I'd be grateful. I've created <https://github.com/httpwg/http-extensions/issues/1598> to track this.

Cheers,

--
Mark Nottingham   https://www.mnot.net/