Full Disclosure mailing list archives
Re: HTTP Digest Integrity: Another look, in light of recent attacks
From: "Timothy D\. Morgan" <tmorgan () vsecurity com>
Date: Wed, 6 Jan 2010 18:17:23 -0800
Hi Dan, Thanks for taking the time to read it.
I haven't been wildly impressed by Digest as implemented in browsers,
Heh, no doubt. When you look into it, it's quite sad how incomplete and inconsistent many implementations are.
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.
Yes, there are some serious limitations to the user interface with Digest auth. I have some ideas for that, which may be cooked up in a future paper. Stay tuned. The level of mitigation right now against TLS renegotiation attacks may be contestable. In fact I'd love to hear of any exploits which workaround digest auth restrictions. Mostly though, I just wanted to throw it out there as food for thought and to give people a possible option if their hair was still on fire after hearing of this latest bug.
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.
I've seen people try to do similar challenge-response protocols in JavaScript, but I've never taken the time to think carefully about how much benefit that provides. Hashing request bodies might be useful against TLS renegotiation, but I'm not sure how verification of responses would work. I guess with lots of AJAX and a lack of checking on the first response. Seems like a lot of work though. Regards, tim _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.grok.org.uk/full-disclosure-charter.html Hosted and sponsored by Secunia - http://secunia.com/
Current thread:
- HTTP Digest Integrity: Another look, in light of recent attacks Timothy D. Morgan (Jan 05)
- Re: HTTP Digest Integrity: Another look, in light of recent attacks Dan Kaminsky (Jan 05)
- Re: HTTP Digest Integrity: Another look, in light of recent attacks Timothy D. Morgan (Jan 06)
- Re: HTTP Digest Integrity: Another look, in light of recent attacks Dan Kaminsky (Jan 07)
- Re: HTTP Digest Integrity: Another look, in light of recent attacks Timothy D. Morgan (Jan 06)
- Re: HTTP Digest Integrity: Another look, in light of recent attacks Dan Kaminsky (Jan 05)