This was DigiNotar. The breach generated around 50 certificates, including certificates for Google, Microsoft, MI6, the CIA, TOR, Mossad, Skype, Twitter, Facebook, Thawte, VeriSign, and Comodo.
Here is a nice writeup for that breach: https://www.securityweek.com/hacker-had-total-control-over-d...
I might be misremembering but I thought one insight from the Snowden documents was that a certain three-letter agency had already accomplished that?