Research unveiled in December of 2008 showed how MD5’s long-known flaws could be actively exploited to attack the real-world Certification Authority infrastructure. This August 2009 presentation demonstrates two new collision classes: the applicability of MD2 pre-image attacks against the primary root certificate for VeriSign and the difficulty of validating X.509 Names contained within PKCS#10 Certificate Requests. It also calls out two possibly unrecognized vectors for implementation flaws that have been problematic in the past: the ASN.1 BER decoder required to parse PKCS#10 and the potential for SQL injection from text contained within its requests.
The implications of these attacks are larger than some have realized-first, because Client Authentication is sometimes tied to X.509, and second, because Extended Validation certificates were only intended to stop phishing attacks from names similar to trusted brands. As per the work of Adam Barth and Collin Jackson, EV does not, in fact, prevent an attacker who can synthesize or acquire a “low assurance” certificate for a given name from acquiring the “green bar” EV experience.