Mozilla removed a newer Turktrust root CA certificate that had been added in the beta version of Firefox 18 and Google also said that it will update Chrome in January to no longer display Extended Validation (EV) status for certificates issued by Turktrust. However, the main Turktrust root CA certificates, including the one that was used to sign the bad sub-CA certificates, have not been removed from either browser. Both companies said that they might decide to take additional actions after further discussion.
Microsoft did not express any intention to completely remove the Turktrust root CA certificates from the Windows trusted certificate store either.
Security experts have long warned that having hundreds of certificate authorities trusted by default in browsers poses a big security risk, because if any of them is compromised it can impact the whole ecosystem. This happened when the CA systems of DigiNotar and a Comodo reseller were compromised and the attackers managed to issue hundreds of rogue certificates for popular domain names. In the case of DigiNotar, the certificates were even used to spy on a large number of users in Iran.
The existence of subordinate CAs poses even bigger risks, because they are usually not held up to the same standards as the CAs they inherit their trust from. Some CAs don't even disclose the sub-CA certificates they issue.
"I have spent the past couple of years trying to convince Mozilla to strengthen their requirements so that CAs must disclose all subordinate certificates that they have issued, so that researchers can better map the risk landscape and so that users can make more informed trust decisions and detect unexpected subordinates," Schultze said in a blog post. "They're getting closer, but it is taking an awfully long time."
In February 2012, certificate authority Trustwave revealed that it had issued a sub-CA certificate that enabled an unnamed private company to spy on SSL-protected connections within its corporate network. Trustwave defended itself by saying that this is a common practice in the industry.