Comodo Attack Sparks SSL Certificate Security Discussions

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The revocation failure is mostly on the browser side, opined Pescatore.

“Browsers generally either don’t check revocation, or only check it on publisher (vs. server) certificates,” he noted. “Even when it is turned on, some browsers interpret a lack of response as ‘the certificate is OK.’ Plus, there has been absolutely no investment in public education by the CA/Browser forum so that normal human beings would even know what to do even if their browser did say ‘The certificate for this site has been revoked. Do you want to proceed?’”

Comodo CEO Melih Abdulhayoglu said the company contacted browser vendors so they could patch after the situation was discovered. Microsoft, Google and Mozilla all issued updates in response to the situation. Still, security researcher Jacob Appelbaum argued in a blog post that Comodo should not have waited eight days before disclosing the attack to the public.

“The browsers have dropped the ball and they have chosen to fail open in nearly every single case; an attacker who is able to MITM (man-in-the-middle) SSL/TLS will also MITM the OCSP/CRL requests…Browsers should give insecure CA keys an Internet Death Sentence rather than expose the users of the browsers to known problems,” he blogged.

Comodo’s CEO defended the company’s approach to disclosure, telling CRN there was no point of announcing the situation to the general public before the browser vendors fixed the issue.

“The attack model here points to people trying to control at the DNS [Domain Name System] level…taking a certificate for Google and putting [it] to a different Website isn’t going to work,” Abdulhayoglu said. “This is why you need to have access to DNS infrastructure. So those certificates, without the ability to have access to DNS infrastructure (are) totally useless.”

Last year, Comodo proposed the idea of establishing a body called the certification authority authorization [CAA] to help CAs fight certificate fraud.

“If that standard was deployed, this attack would be useless,” he explained. “The bigger problem that we’re facing is the untrusted and unsecure nature of the DNS infrastructure,” he added. “If DNS was trusted and secure, what could these certificates do? Nothing.”


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