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Re: [TLS] [pkix] New version of Multiple OCSP mode of Certificate Status

Peter Gutmann <pgut001@cs.auckland.ac.nz> Thu, 05 August 2010 09:53 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: mrex@sap.com
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Date: Thu, 05 Aug 2010 21:53:25 +1200
Cc: pkix@ietf.org, tls@ietf.org
Subject: Re: [TLS] [pkix] New version of Multiple OCSP mode of Certificate Status
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Martin Rex <mrex@sap.com> writes:

>Now if the browser performs AIA retrieval for unverified server certs, then
>this scenario is suddenly completely unprotected against active attacks where
>the attacker serves a manufactured server certificate with crafted AIA (but
>matching the server identity of the online banking account in the CN= or
>dNSName SAN.

Even more entertaining is sending in a client cert chain with a sequence of 
AIAs pointing to portions of common RFC 1918 address spaces.  You then time 
the server response time based on whether it gets an immediate ECONNREFUSED or 
similar, or has to time out.  First you check for the presence of a server at 
a given address using some common port like 445 and then you fingerprint it to 
see what's running, e.g. SQL server.  Hey presto, remote internal-network 
scanning via certificates.

(Just for the record, I had permission from the server admin to do this, at
least the second time I tried it :-).

Peter.

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