full-disclosure-uk January 2010 archive
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full-disclosure-uk: Re: [Full-disclosure] HTTP Digest Integrity:

Re: [Full-disclosure] HTTP Digest Integrity: Another look, in light of recent attacks

From: Dan Kaminsky <dan_at_nospam>
Date: Wed Jan 06 2010 - 07:59:37 GMT
To: "Timothy D. Morgan" <tmorgan@vsecurity.com>


I haven't been wildly impressed by Digest as implemented in browsers, but it's a legitimate point that Digest has of at least *some* of the URI embedded into it, so the TLS reneg attack can be somewhat mitigated by leveraging that. Empirically though, this is going to be a big pain in the butt, not least of which is the dramatic change to the user experience.

Ultimately, far and away the most common forms of auth are cookie based, with hidden variables being a close second. In both of these the password is accessible to the DOM. So the raw material is there to add an integrity layer to at least sensitive HTTPS transactions (everything is worthless for HTTP). But an advantage of your approach is that it applies generically to all browser/site communication, including Javascript containers like <script src> and <link rel=stylesheet>. There's no way to register a hook that gets triggered whenever a site hits a particular URI within a domain, to add the validator, in JS. It just happens in Digest.

On Wed, Jan 6, 2010 at 2:15 AM, Timothy D. Morgan <tmorgan@vsecurity.com>wrote:

>
> Hello,
>
> Some of you may be interested in this short technical note which
> includes some recent observations about TLS renegotiation and other
> issues:
> http://www.vsecurity.com/download/papers/HTTPDigestIntegrity.pdf
>
> Comments welcome,
> tim
>
>
>
> Introduction
> ============
> Recent history has proven that web communications security is highly
> lacking in redundancy. That is, simple breaks in common protocols,
> such as SSL/TLS or the authentication mechanisms which support it,
> often lead to catastrophic gaps in security. Recent examples of this
> fragile architecture abound, and even when protocols and
> implementations themselves are sound, research indicates browser user
> interfaces continue to leave room for serious attacks.
>
> This paper explores how the seldom-used HTTP digest authentication
> protocol can be used to mitigate certain recent forms of attack,
> including SSL/TLS renegotiation and some types of HTTP request
> smuggling.
>
> ...
>
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