SUMMARY: Comodo was informed by security researchers Florian Heinz and Martin Kluge that on 23rd September 2016 they had been able to obtain a server authentication certificate  from Comodo for a domain which they did not own or control.
The researchers shared their discovery with Comodo and this assisted Comodo to ensure that no further such certificates were issued. DOMAIN CONTROL VALIDATION One of the methods that Comodo uses to validate that a certificate applicant owns or controls a domain to be included in the subjectAlternativeName of a server authentication certificate is set out in the CA/B Forum's Baseline Requirements document  at section 18.104.22.168.2. That method may be summarized as the sending of an email to an email address (and obtaining a confirming response) where the email is identified as belonging to the Domain Name Registrant, technical contact, or administrative contract as listed in the WHOIS record of the domain. For the TLDs .eu and .be the registries offer only a redacted port 43 WHOIS service which does not include the contact email addresses. They also offer a web-based WHOIS service which presents the contact email addresses, but which does so in the form of a graphical image in a page instead of text. For these TLDs (.eu and .be) we were using an OCR system to read the contact email addresses. The researchers disclosed to Comodo that, while obtaining a certificate from Comodo for a domain that they did control, Comodo's certificate application process presented them with an email address which was not the same as they had registered in WHOIS but which was substantially similar. They inferred from the nature of the difference between the email addresses that the difference was due to an error in reading the email address, most likely by OCR (Optical Character Recognition). They verified that the error in transcribing the email address led to a vulnerability in the certificate application process by identifying a domain name which was also subject to the OCR transcription error and, by registering a domain with the name produced by the transcription error, were able to obtain a certificate from Comodo for the domain name which was subject to the transcription error despite them not controlling it. The domain that they used for their proof of concept was a1-telekom.eu The registrant email address in the WHOIS entry was domain.bill...@a1telekom.at <mailto:domain.bill...@a1telekom.at> which was misread by OCR as domain.bill...@altelekom.at <mailto:domain.bill...@altelekom.at> (the "1" in a1telekom.at was detected as a lower case 'L') IMMEDIATE RESPONSE Comodo's immediate response to the disclosure was to revoke the identified certificate and to disable the use of OCR in the interpretation of WHOIS responses for the validation new certificate requests. INVESTIGATION OF SCOPE Comodo used an OCR system to interpret WHOIS information from 2 TLDs. The TLDs were .be and .eu . Comodo used OCR for the WHOIS on these two domains between 27-JUL-2016 and 28-SEP-2016. Comodo is performing a thorough review of all server certificates issued by Comodo between those dates for domains on the .be and .eu TLDs which used the domain control validation method described in 22.214.171.124.2 of the BRs. The review is ongoing but no other examples have been found of certificates issued as a consequence of OCR mis-reads. WHOIS Comodo notes that the port 43 WHOIS service provided by most registries is a valuable source of information for CAs and for other parties who have a legitimate need to contact domain name registrants. Some domain registrars provide registrants with a means to effectively opt-out of having their contact details made public through the port 43 WHOIS server, or otherwise, by providing a 'privacy' or 'anonymization' service whose details appear in the WHOIS results for the domain instead of those of the registrant. Comodo understands that some registrants will not want to be identified and supports their right to a choice as to whether they should be identified in WHOIS. Comodo understands that some registries do not offer a port 43 WHOIS service because they are not able to do so. There are some registries for small or poor regions where we cannot expect technical excellence. Comodo finds it regrettable that some registries choose to offer a port 43 WHOIS service which redacts information for all registrants which even the registry themselves would normally consider to be public. We find it even more regrettable that a sub-set of those registries refuse to consider offering unredacted access to that information even when contractual and/or commercial terms (including binding restrictions on the use of that information) are offered. Robin Alden Comodo CA Ltd.  https://crt.sh/?id=47045653  https://cabforum.org/wp-content/uploads/CA-Browser-Forum-BR-1.4.1.pdf  http://www.heise.de/newsticker/meldung/Zertifikats-Klau-Fatale-Sehschwaeche- bei-Comodo-3354229.html
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