Compromise of SSL-protected communication — Mozilla

IOActive security researcher Dan Kaminsky reported a mismatch in the treatment of domain names in SSL certificates between SSL clients and the Certificate Authorities (CA) which issue server certificates. In particular, if a malicious person requested a certificate for a host name with an invalid null character in it most CAs would issue the certificate if the requester owned the domain specified after the null, while most SSL clients (browsers) ignored that part of the name and used the unvalidated part in front of the null. This made it possible for attackers to obtain certificates that would function for any site they wished to target. These certificates could be used to intercept and potentially alter encrypted communication between the client and a server such as sensitive bank account transactions.