Re: [http-state] Security considerations overview

Adam Barth <ietf@adambarth.com> Tue, 02 March 2010 22:52 UTC

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From: Adam Barth <ietf@adambarth.com>
Date: Tue, 2 Mar 2010 14:52:01 -0800
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To: Tyler Close <tyler.close@gmail.com>
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Subject: Re: [http-state] Security considerations overview
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On Tue, Mar 2, 2010 at 2:38 PM, Tyler Close <tyler.close@gmail.com> wrote:
> On Tue, Mar 2, 2010 at 1:54 PM, Adam Barth <ietf@adambarth.com> wrote:
>> On Tue, Mar 2, 2010 at 1:46 PM, David Morris <dwm@xpasc.com> wrote:
>>> On Tue, 2 Mar 2010, Adam Barth wrote:
>>>> On Tue, Mar 2, 2010 at 11:42 AM, David Morris <dwm@xpasc.com> wrote:
>>>> > On Tue, 2 Mar 2010, Adam Barth wrote:
>>>> >>         <t>Transport-layer encryption, such as HTTPS, is insufficient to
>>>> >>         prevent a network attacker from altering a victim's cookies because
>>>> >>         the cookie protocol does not provide integrity.  By default, cookies
>>>> >>         are transmitted in the clear, where their confidentiality can be
>>>> >>         compromised by a network attacker.</t>
>>>> >
>>>> > I don't under stand how the second sentence extends the thought in the
>>>> > first sentence. It seems in conflict in the sense that HTTPS is not
>>>> > sending cookies in the clear and use of HTTPS is generally recommended
>>>> > as the way to avoid compromise by network hackers. What am I missing?
>>>>
>>>> If even if you use the cookie protocol exclusively over HTTPS, the
>>>> default is still to send the cookies in the clear (i.e., the
>>>> secure-only-flag defaults to false).
>>>
>>> But wrapped inside of the HTTPS stream, it is like the remainder of
>>> everything about the HTTP request (including headers), sans any general
>>> HTTPS vulnerabilities, not visible on the network to hackers.
>>>
>>> If you are trying to say that a cookie sent on an HTTPS connection from
>>> a server will be returned on any non-HTTPS connections and hence be
>>> vulnerable in that context, the paragraph doesn't say that. To me it
>>> says that even if my WHOLE application is HTTPS based, the cookies
>>> are vulnerable on the network.
>>
>> Even if your whole application is HTTPS-based, the cookies are
>> vulnerabile to active network attackers.  That is a true statement,
>> and precisely the security problem we're trying to point out in that
>> sentence.  Maybe this is a better formulation?
>>
>> [[
>>        In addition, by default,
>>        the cookie protocol does not provide confidentiality from network
>>        attackers.
>> ]]
>
> A reader could again misinterpret that formulation and so believe the
> problem can be fixed by using HTTPS, which is incorrect.
>
> I think this thread is a good indication that providing an "executive
> summary" at the start of the Security section could be very effective
> in communicating the rationale behind the prior recommendation against
> using cookies in new applications. Succinct statements can sometimes
> communicate better than detailed descriptions.

Does this help?

[[
        In addition, by default,
        the cookie protocol does not provide confidentiality from network
        attackers, even when used over HTTPS.
]]

Adam