Posted by Virus Bulletin on Mar 24, 2011
Certificates revoked, but browsers still need to be updated.
Comodo, a major vendor of SSL certificates, has admitted to one of its affiliates' servers being hacked, leading to nine rogue SSL certificates for popular domains to be issued.
SSL (secure socket layer) allows for traffic over the Internet that can not be intercepted by intermediates. HTTP over SSL (commonly known as HTTPS) is essential for confidential traffic, such as password and online banking details, between users and websites. More and more websites, including recently Facebook and Twitter, allow for all the traffic to be sent via HTTPS.
However, one of the weaknesses of the protocol is that it does not guarantee that the website is indeed the one it claims to be. That is why a number of trusted organisations, of which Comodo is one, sell certificates that provide proof to the user's browser that communication is happening with the right website.
A hacker trying to re-route traffic attempting to access a certain website (to instead go to a malicious site) - for instance by installing malware on a computer, or by hacking into DNS servers - is significantly more likely to succeed if they can obtain a certificate for the domain. This appears to have happened at Comodo, where certificates were issued for, among others, Google, Yahoo, Skype and Mozilla.
Certificate issuers have the option to revoke certificates and indeed, Comodo did so immediately upon discovering the hack. However, as pointed out by Sophos's Mike Wood in his VB2010 presentation on signatures, most browsers do not check for revoked certificates by default. It is thus both important and understandable that both Microsoft (whose Internet Explorer 9 does have the correct defaults) and Mozilla have released updates that recognize the rogue certificates.
In a statement on its blog, Comodo said the initial attack was performed from an IP address in Iran. While the company acknowledges that this may be a false trail laid by the attacker, it also points out that issuing rogue certificates, combined with re-routing traffic, may be a very useful tool for governments who want to spy on their citizens.