[cabfpub] Ballot 190

Tim Shirley TShirley at trustwave.com
Tue May 2 14:49:41 UTC 2017

Peter’s examples are certainly cases for which we shouldn’t allow reuse.  But I wonder if it is possible to constrain reuse based on things like this that we know are vulnerable, as opposed to blanket disallowing everything that doesn’t exactly follow the new rules.  As a concrete example, Trustwave began following the guidance on this method while it was still evolving, so there was a period of time in which we were doing our domain validation in a “/.well-known/certificate” directory instead of “/.well-known/pki-validation”, because that was the path defined in an earlier draft of the changes.  I don’t think anyone could argue that was less secure, but since it doesn’t follow to the letter, those validations would need to be re-done.



From: Public [mailto:public-bounces at cabforum.org] On Behalf Of Peter Bowen via Public
Sent: Friday, April 28, 2017 12:31 PM
To: CA/Browser Forum Public Discussion List
Cc: Peter Bowen
Subject: Re: [cabfpub] Ballot 190

   On Apr 28, 2017, at 9:06 AM, Kirk Hall via Public <public at cabforum.org<mailto:public at cabforum.org>> wrote:

   1.  It appears from various comments over time that your biggest concern about re-use of prior validation data relates to method – Agreed Upon Change to Website.  Old method 6 required “Having the Applicant demonstrate practical control over the FQDN by making an agreed-upon change to information found on an online Web page identified by a uniform resource identifier containing the FQDN”

   New method 6 requires specified content be posted to a "/.well‐known/pki‐validation" directory, which no CA has ever done (because this path is brand new, and created for the updated version of this validation method).  So prohibiting reuse of data collected under old method 6 will necessarily require revalidation of ALL domains ever validated under old method 6.  As I indicated on the CABF teleconference yesterday, this will require some CAs (including Entrust) to manually review EVERY domain validation we have done to determine which used old method 6, versus other approved methods.  This would be a massive undertaking, and something CAs won’t want to do unless there is a demonstrated security need.

   Can you share with us the facts, data, evidence, etc. that leads you to believe that the domain validations previously done under old method 6 pose a significant security threat to users?  Any statistics to back this up?  I’m not challenging you, I’m just asking you for data that supports what you want us to do.  We are not aware of any instance where we used old method 6 and later discovered that the domain should not have been authorized for the customer.


   I did some research on this back when we were working on ballot 169.  See https://cabforum.org/pipermail/public/2016-April/007504.html<https://scanmail.trustwave.com/?c=4062&d=rPWD2QU5C4Ub0yJc3Lnmmca2cLs-GOxx2fN_E9uAfg&s=5&u=https%3a%2f%2fcabforum%2eorg%2fpipermail%2fpublic%2f2016-April%2f007504%2ehtml> and https://cabforum.org/pipermail/public/2016-April/007506.html<https://scanmail.trustwave.com/?c=4062&d=rPWD2QU5C4Ub0yJc3Lnmmca2cLs-GOxx2f5yENrRLg&s=5&u=https%3a%2f%2fcabforum%2eorg%2fpipermail%2fpublic%2f2016-April%2f007506%2ehtml>

   We know that all the following were valid under the old method 6:

   - Allowing the certificate requester to specify the URI.  For example, if the certificate wanted shop.example.com<http://scanmail.trustwave.com/?c=4062&d=rPWD2QU5C4Ub0yJc3Lnmmca2cLs-GOxx2fAgQYXWLA&s=5&u=http%3a%2f%2fshop%2eexample%2ecom>, the requester could say “check at http://shop.example.com/tmp/uploads/foo.txt<http://scanmail.trustwave.com/?c=4062&d=rPWD2QU5C4Ub0yJc3Lnmmca2cLs-GOxx2f8iEIXVLA&s=5&u=http%3a%2f%2fshop%2eexample%2ecom%2ftmp%2fuploads%2ffoo%2etxt>” for the agreed upon change

   - Looking for the change anywhere in the page.  The CA would give the requester a token to put on the website and then look for it to appear somewhere on the page.  This is a huge problem for sites that have public comments, message boards, or user-editable content.  For example, validate “control” of www.ibm.com<http://scanmail.trustwave.com/?c=4062&d=rPWD2QU5C4Ub0yJc3Lnmmca2cLs-GOxx2aAkHIbUKA&s=5&u=http%3a%2f%2fwww%2eibm%2ecom> by posting a message containing the token at https://www.ibm.com/developerworks/community/forums/html/public<https://scanmail.trustwave.com/?c=4062&d=rPWD2QU5C4Ub0yJc3Lnmmca2cLs-GOxx2aVxFdfVeQ&s=5&u=https%3a%2f%2fwww%2eibm%2ecom%2fdeveloperworks%2fcommunity%2fforums%2fhtml%2fpublic>

   - Simply looking for the existence of a  file by name.  For example telling the customer to create http://<FQDN>/adfa24r43aefwaer2442.txt<http://%3cFQDN%3e/adfa24r43aefwaer2442.txt> and not caring about the content.

   - Looking for a content to be returned from the server that was included in the URL and not checking the HTTP return code.

   I would also note that other “old” methods have similar issues.  For example, there was no requirement that email validation used a unique token per request.  It would have been valid to send an email saying “Does this email work?” to the domain owner and using an out-of-office auto-reply as proof of “communication”, as the requirement was only “Communicating with” the email address.

   Does that help explain the concern?



   From: Ryan Sleevi [mailto:sleevi at google.com]

   Sent: Friday, April 28, 2017 6:09 AM
   To: Kirk Hall <Kirk.Hall at entrustdatacard.com<mailto:Kirk.Hall at entrustdatacard.com>>
   Cc: CA/Browser Forum Public Discussion List <public at cabforum.org<mailto:public at cabforum.org>>; Wayne Thayer <wthayer at godaddy.com<mailto:wthayer at godaddy.com>>
   Subject: [EXTERNAL]Re: [cabfpub] Ballot 190

   On Fri, Apr 28, 2017 at 1:32 AM, Kirk Hall <Kirk.Hall at entrustdatacard.com<mailto:Kirk.Hall at entrustdatacard.com>> wrote:

      One other comment.  Remember that for the last few months, new Methods 1-4 and 7-10 were actually included under Method 11 “any other method” after Ballot 181’s effective date, and that situation will continue until the effective date of Ballot 190.  Also, the same is true for any validations that followed old Method 7 “any other method” prior to the effective date of Ballot 169.  So be very careful in saying anything in Ballot 190 that would invalidate validations done prior to Ballot 190 under “any other method” so long as they complied with any of Methods 1-10 of the new methods or Methods 1-6 of the old methods.

      I would be open to saying that any prior vetting done under old Method 7 or more recent Method 11 “any other method” must be revalidated upon the effective date of Ballot 190 IF they did not follow EITHER Methods 1-6 (as the existed before Ballot 169) or Methods 1-10 (as put forward in Ballot 169).  In other words, the ONLY validations that have to be redone before the expiration of the re-use period are validations that were done that did not comply with either old Methods 1-6 or new Methods 1-10.  That should flush out any unknown and unsecure validations that occurred in the past.

   Not quite, because if you recall, Google's interest in reforming these began with the fact that a website demonstration of control was not secure. That is, under pre-169 is not acceptable.

   Kirk, given your support for other forms of indicating that a CA has performed extra diligence, such as the inclusion of OV certificates, would you be supportive in general of a means of expressing, within a certificate, conformance with the 'new' validation methods, so that subscribers can have assurances of the security?

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   Public at cabforum.org<mailto:Public at cabforum.org>

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