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 22.214.171.124.2.
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
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
The registrant email address in the WHOIS entry was
which was misread by OCR as
(the "1" in a1telekom.at was detected
as a lower case 'L')
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
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 126.96.36.199.2 of the BRs.
The review is ongoing but no other examples have been found of certificates
issued as a consequence of OCR mis-reads.
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
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.
Comodo CA Ltd.