This post attracted my attention because a company I used to work for a few years ago used personal certs as to limit access to administrative pages. In that implementation, the website (IIS 5.0) was configured to restrict access to the admin pages by personal cert, then they used some ASP to look at certain certificate characteristics, including the CN or Common Name property. In an attempt to test the security of the admin pages, I trawled through the website looking for staff email addresses, issued myself a cert, and gave it valid CN and other properties. I tried connecting to the admin pages, and a window popped up asking me for my personal cert, but the cert list was empty. It turned out for some reason that only certs issued by trusted certificate authorities would appear in my list. So, I looked for a trusted cert authority that I could use to generate a certificate with the right properties. It has been a while now, so I can't remember who I used, but I did find one provider that would let me specify a common name in such a way that it appeared to be a Thawte certificate. Unfortunately, part of the sign up procedure was specifying your email address. If I gave the email address of a valid employee, THEY would receive the email containing the certificate. That would mean I would need to steal their mail. Break in, send them an email with a trojan that would grab the mail for me, whatever. So I stopped at this point. I had done enough to prove that there was a chance, a small chance, that someone could generate a certificate that would trick our system. It would require someone to be able to grab someone's mail, but we all know about a billion stupid viruses that can do that. An employee of a certification authority would have an easy time doing it. Now.... does this mean that all applications that use personal certs as a "key" are vulnerable? No. In this instance, certain parts of a cert were being looked at by some ASP, and that really wasn't enough to guarantee that the cert offered by the client was the real thing. Before I could suggest an better solution, we totally changed our admin access method, and certs didn't play a part. Anyway, I haven't dealt with certs very much since then, so I don't know what other ways people use them, check their validity, etc. Perhaps the more experienced people in this list can through their two cents worth in. BRYAN -----Original Message----- From: Darren Craig [mailto:darren.craigat_private] Sent: Monday, January 28, 2002 8:00 AM To: pen-testat_private Subject: Can you impersonate a client side cert?? Hi All, I have been reading a paper which was published back in Feb 2001 by a company call Sensepost which says that there is a way to impersonate a users client side cert by using the same common name. Does anybody have any experience of doing this or is it even possible considering that the users public part of the cert would be installed on the web server? Darren ****************************************************************** Privileged, confidential and/or copyright information may be contained in this e-mail. This e-mail is for the use only of the intended addressee. If you are not the intended addressee, or the person responsible for delivering it to the intended addressee, you may not copy, forward, disclose or otherwise use it or any part of it in any way whatsoever, to do so is prohibited and may be unlawful. If you receive this e-mail by mistake please advise the sender immediately by using the reply facility in your e-mail software. Celare Limited may monitor the content of e-mails sent and received via its network for the purposes of ensuring compliance with its policies and procedures. This message is subject to and does not create or vary any contractual relationship between Celare Limited and you. Thank you. ****************************************************************** ---------------------------------------------------------------------------- This list is provided by the SecurityFocus Security Intelligence Alert (SIA) Service. For more information on SecurityFocus' SIA service which automatically alerts you to the latest security vulnerabilities please see: https://alerts.securityfocus.com/ _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com ---------------------------------------------------------------------------- This list is provided by the SecurityFocus Security Intelligence Alert (SIA) Service. For more information on SecurityFocus' SIA service which automatically alerts you to the latest security vulnerabilities please see: https://alerts.securityfocus.com/
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