SUMMARY: Comodo was alerted at September 24 2016 07:11 BST to a report [1] of the issuance by Comodo of a Server Authentication certificate [2] that includes 'sb' as a SAN:dNSName. sb is a gTLD.
OUR CURRENT (PRE-BALLOT 169) POLICY REGARDING 'www': To establish context, first we will explain our policy with regard to the 'www' sub-domain, for which the common link to the base domain is well known [3]. When we use an 'agreed-upon change to website' method to prove domain control, we consider proof of control of 'www.<base_domain>' as also proving control of '<base_domain>' (except where '<base_domain>' is a public suffix). We don't give any other sub-domain this treatment, only 'www'. We believe that the currently enforced and audited (pre-ballot 169) BRs permit us to do this under section 3.2.2.4 method 7. ADDITIONAL FQDN FOR DOMAIN NAME MISMATCH REDUCTION: When an applicant requests a certificate for the FQDN '<base_domain>', we also add the FQDN 'www.<base_domain>' into the certificate, and vice-versa. This has been a fairly common practice amongst CAs for several years. ROOT CAUSE: The applicant requested a certificate for 'www.sb'. Although our code correctly identified that the base domain ('sb') was a public suffix, there was an error of logic that failed to prevent the certificate from being issued in this case. REMEDIATION: We investigated the matter promptly, identified the root cause, and within a few hours we had deployed a bugfix to correct the error of logic, so that issuance of a certificate where the Additional FQDN is a public suffix is now blocked as intended. TRANSPARENCY: The bugfix we deployed on September 24 had actually been prepared several weeks earlier, after we'd been alerted (by [4]) to a similar occurrence: we had issued 3 certificates [5] for 'www.tc' (a valid registered domain) that also included 'tc' (a public suffix) as a dNSName. Since 'www.tc' and 'tc' both belong to the same entity, we took the view that the cert had not been misissued and that an incident report was not warranted. We also took the view that this flaw did not require an urgent hotfix. Unfortunately, scheduled deployment of the bugfix did not occur before the 'sb' certificate [2] was issued. Today we performed an exhaustive search of all the server authentication certificates we've issued since November 1 2015, and as a result we found just one further certificate [6] in which we'd included a public suffix (rivne.ua) due to this bug. [1] https://www.mail-archive.com/dev-security-policy@lists.mozilla.org/msg04233. html [2] https://crt.sh/?id=34242572 [3] https://en.wikipedia.org/wiki/World_Wide_Web#WWW_prefix [4] https://crt.sh/?cablint=1+week [5] https://crt.sh/?dNSName=tc [6] https://crt.sh/?id=11091687 -- Rob Stradling Robin Alden Comodo CA Ltd.
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